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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  linux/mm/filemap.c
  *
  * Copyright (C) 1994-1999  Linus Torvalds
  */
 
 /*
  * This file handles the generic file mmap semantics used by
  * most "normal" filesystems (but you don't /have/ to use this:
  * the NFS filesystem used to do this differently, for example)
  */
 #include <linux/export.h>
 #include <linux/compiler.h>
 #include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/sched/signal.h>
 #include <linux/uaccess.h>
 #include <linux/capability.h>
 #include <linux/kernel_stat.h>
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/mman.h>
 #include <linux/pagemap.h>
 #include <linux/file.h>
 #include <linux/uio.h>
 #include <linux/error-injection.h>
 #include <linux/hash.h>
 #include <linux/writeback.h>
 #include <linux/backing-dev.h>
 #include <linux/pagevec.h>
 #include <linux/security.h>
 #include <linux/cpuset.h>
 #include <linux/hugetlb.h>
 #include <linux/memcontrol.h>
 #include <linux/shmem_fs.h>
 #include <linux/rmap.h>
 #include <linux/delayacct.h>
 #include <linux/psi.h>
 #include <linux/ramfs.h>
 #include <linux/page_idle.h>
 #include <linux/migrate.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 #include "internal.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/filemap.h>
 
 /*
  * FIXME: remove all knowledge of the buffer layer from the core VM
  */
 #include <linux/buffer_head.h> /* for try_to_free_buffers */
 
 #include <asm/mman.h>
 
 /*
  * Shared mappings implemented 30.11.1994. It's not fully working yet,
  * though.
  *
  * Shared mappings now work. 15.8.1995  Bruno.
  *
  * finished 'unifying' the page and buffer cache and SMP-threaded the
  * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
  *
  * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
  */
 
 /*
  * Lock ordering:
  *
  *  ->i_mmap_rwsem      (truncate_pagecache)
  *    ->private_lock        (__free_pte->block_dirty_folio)
  *      ->swap_lock     (exclusive_swap_page, others)
  *        ->i_pages lock
  *
  *  ->i_rwsem
  *    ->invalidate_lock     (acquired by fs in truncate path)
  *      ->i_mmap_rwsem      (truncate->unmap_mapping_range)
  *
  *  ->mmap_lock
  *    ->i_mmap_rwsem
  *      ->page_table_lock or pte_lock   (various, mainly in memory.c)
  *        ->i_pages lock    (arch-dependent flush_dcache_mmap_lock)
  *
  *  ->mmap_lock
  *    ->invalidate_lock     (filemap_fault)
  *      ->lock_page     (filemap_fault, access_process_vm)
  *
  *  ->i_rwsem           (generic_perform_write)
  *    ->mmap_lock       (fault_in_readable->do_page_fault)
  *
  *  bdi->wb.list_lock
  *    sb_lock           (fs/fs-writeback.c)
  *    ->i_pages lock        (__sync_single_inode)
  *
  *  ->i_mmap_rwsem
  *    ->anon_vma.lock       (vma_adjust)
  *
  *  ->anon_vma.lock
  *    ->page_table_lock or pte_lock (anon_vma_prepare and various)
  *
  *  ->page_table_lock or pte_lock
  *    ->swap_lock       (try_to_unmap_one)
  *    ->private_lock        (try_to_unmap_one)
  *    ->i_pages lock        (try_to_unmap_one)
  *    ->lruvec->lru_lock    (follow_page->mark_page_accessed)
  *    ->lruvec->lru_lock    (check_pte_range->isolate_lru_page)
  *    ->private_lock        (page_remove_rmap->set_page_dirty)
  *    ->i_pages lock        (page_remove_rmap->set_page_dirty)
  *    bdi.wb->list_lock     (page_remove_rmap->set_page_dirty)
  *    ->inode->i_lock       (page_remove_rmap->set_page_dirty)
  *    ->memcg->move_lock    (page_remove_rmap->lock_page_memcg)
  *    bdi.wb->list_lock     (zap_pte_range->set_page_dirty)
  *    ->inode->i_lock       (zap_pte_range->set_page_dirty)
  *    ->private_lock        (zap_pte_range->block_dirty_folio)
  *
  * ->i_mmap_rwsem
  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
  */
 
 static void page_cache_delete(struct address_space *mapping,
                    struct folio *folio, void *shadow)
 {
     XA_STATE(xas, &mapping->i_pages, folio->index);
     long nr = 1;
 
     mapping_set_update(&xas, mapping);
 
     /* hugetlb pages are represented by a single entry in the xarray */
     if (!folio_test_hugetlb(folio)) {
         xas_set_order(&xas, folio->index, folio_order(folio));
         nr = folio_nr_pages(folio);
     }
 
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
     xas_store(&xas, shadow);
     xas_init_marks(&xas);
 
     folio->mapping = NULL;
     /* Leave page->index set: truncation lookup relies upon it */
     mapping->nrpages -= nr;
 }
 
 static void filemap_unaccount_folio(struct address_space *mapping,
         struct folio *folio)
 {
     long nr;
 
     VM_BUG_ON_FOLIO(folio_mapped(folio), folio);
     if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(folio_mapped(folio))) {
         pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
              current->comm, folio_pfn(folio));
         dump_page(&folio->page, "still mapped when deleted");
         dump_stack();
         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
         if (mapping_exiting(mapping) && !folio_test_large(folio)) {
             int mapcount = page_mapcount(&folio->page);
 
             if (folio_ref_count(folio) >= mapcount + 2) {
                 /*
                  * All vmas have already been torn down, so it's
                  * a good bet that actually the page is unmapped
                  * and we'd rather not leak it: if we're wrong,
                  * another bad page check should catch it later.
                  */
                 page_mapcount_reset(&folio->page);
                 folio_ref_sub(folio, mapcount);
             }
         }
     }
 
     /* hugetlb folios do not participate in page cache accounting. */
     if (folio_test_hugetlb(folio))
         return;
 
     nr = folio_nr_pages(folio);
 
     __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
     if (folio_test_swapbacked(folio)) {
         __lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);
         if (folio_test_pmd_mappable(folio))
             __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
     } else if (folio_test_pmd_mappable(folio)) {
         __lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
         filemap_nr_thps_dec(mapping);
     }
 
     /*
      * At this point folio must be either written or cleaned by
      * truncate.  Dirty folio here signals a bug and loss of
      * unwritten data - on ordinary filesystems.
      *
      * But it's harmless on in-memory filesystems like tmpfs; and can
      * occur when a driver which did get_user_pages() sets page dirty
      * before putting it, while the inode is being finally evicted.
      *
      * Below fixes dirty accounting after removing the folio entirely
      * but leaves the dirty flag set: it has no effect for truncated
      * folio and anyway will be cleared before returning folio to
      * buddy allocator.
      */
     if (WARN_ON_ONCE(folio_test_dirty(folio) &&
              mapping_can_writeback(mapping)))
         folio_account_cleaned(folio, inode_to_wb(mapping->host));
 }
 
 /*
  * Delete a page from the page cache and free it. Caller has to make
  * sure the page is locked and that nobody else uses it - or that usage
  * is safe.  The caller must hold the i_pages lock.
  */
 void __filemap_remove_folio(struct folio *folio, void *shadow)
 {
     struct address_space *mapping = folio->mapping;
 
     trace_mm_filemap_delete_from_page_cache(folio);
     filemap_unaccount_folio(mapping, folio);
     page_cache_delete(mapping, folio, shadow);
 }
 
 void filemap_free_folio(struct address_space *mapping, struct folio *folio)
 {
     void (*free_folio)(struct folio *);
     int refs = 1;
 
     free_folio = mapping->a_ops->free_folio;
     if (free_folio)
         free_folio(folio);
 
     if (folio_test_large(folio) && !folio_test_hugetlb(folio))
         refs = folio_nr_pages(folio);
     folio_put_refs(folio, refs);
 }
 
 /**
  * filemap_remove_folio - Remove folio from page cache.
  * @folio: The folio.
  *
  * This must be called only on folios that are locked and have been
  * verified to be in the page cache.  It will never put the folio into
  * the free list because the caller has a reference on the page.
  */
 void filemap_remove_folio(struct folio *folio)
 {
     struct address_space *mapping = folio->mapping;
 
     BUG_ON(!folio_test_locked(folio));
     spin_lock(&mapping->host->i_lock);
     xa_lock_irq(&mapping->i_pages);
     __filemap_remove_folio(folio, NULL);
     xa_unlock_irq(&mapping->i_pages);
     if (mapping_shrinkable(mapping))
         inode_add_lru(mapping->host);
     spin_unlock(&mapping->host->i_lock);
 
     filemap_free_folio(mapping, folio);
 }
 
 /*
  * page_cache_delete_batch - delete several folios from page cache
  * @mapping: the mapping to which folios belong
  * @fbatch: batch of folios to delete
  *
  * The function walks over mapping->i_pages and removes folios passed in
  * @fbatch from the mapping. The function expects @fbatch to be sorted
  * by page index and is optimised for it to be dense.
  * It tolerates holes in @fbatch (mapping entries at those indices are not
  * modified).
  *
  * The function expects the i_pages lock to be held.
  */
 static void page_cache_delete_batch(struct address_space *mapping,
                  struct folio_batch *fbatch)
 {
     XA_STATE(xas, &mapping->i_pages, fbatch->folios[0]->index);
     long total_pages = 0;
     int i = 0;
     struct folio *folio;
 
     mapping_set_update(&xas, mapping);
     xas_for_each(&xas, folio, ULONG_MAX) {
         if (i >= folio_batch_count(fbatch))
             break;
 
         /* A swap/dax/shadow entry got inserted? Skip it. */
         if (xa_is_value(folio))
             continue;
         /*
          * A page got inserted in our range? Skip it. We have our
          * pages locked so they are protected from being removed.
          * If we see a page whose index is higher than ours, it
          * means our page has been removed, which shouldn't be
          * possible because we're holding the PageLock.
          */
         if (folio != fbatch->folios[i]) {
             VM_BUG_ON_FOLIO(folio->index >
                     fbatch->folios[i]->index, folio);
             continue;
         }
 
         WARN_ON_ONCE(!folio_test_locked(folio));
 
         folio->mapping = NULL;
         /* Leave folio->index set: truncation lookup relies on it */
 
         i++;
         xas_store(&xas, NULL);
         total_pages += folio_nr_pages(folio);
     }
     mapping->nrpages -= total_pages;
 }
 
 void delete_from_page_cache_batch(struct address_space *mapping,
                   struct folio_batch *fbatch)
 {
     int i;
 
     if (!folio_batch_count(fbatch))
         return;
 
     spin_lock(&mapping->host->i_lock);
     xa_lock_irq(&mapping->i_pages);
     for (i = 0; i < folio_batch_count(fbatch); i++) {
         struct folio *folio = fbatch->folios[i];
 
         trace_mm_filemap_delete_from_page_cache(folio);
         filemap_unaccount_folio(mapping, folio);
     }
     page_cache_delete_batch(mapping, fbatch);
     xa_unlock_irq(&mapping->i_pages);
     if (mapping_shrinkable(mapping))
         inode_add_lru(mapping->host);
     spin_unlock(&mapping->host->i_lock);
 
     for (i = 0; i < folio_batch_count(fbatch); i++)
         filemap_free_folio(mapping, fbatch->folios[i]);
 }
 
 int filemap_check_errors(struct address_space *mapping)
 {
     int ret = 0;
     /* Check for outstanding write errors */
     if (test_bit(AS_ENOSPC, &mapping->flags) &&
         test_and_clear_bit(AS_ENOSPC, &mapping->flags))
         ret = -ENOSPC;
     if (test_bit(AS_EIO, &mapping->flags) &&
         test_and_clear_bit(AS_EIO, &mapping->flags))
         ret = -EIO;
     return ret;
 }
 EXPORT_SYMBOL(filemap_check_errors);
 
 static int filemap_check_and_keep_errors(struct address_space *mapping)
 {
     /* Check for outstanding write errors */
     if (test_bit(AS_EIO, &mapping->flags))
         return -EIO;
     if (test_bit(AS_ENOSPC, &mapping->flags))
         return -ENOSPC;
     return 0;
 }
 
 /**
  * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
  * @mapping:    address space structure to write
  * @wbc:    the writeback_control controlling the writeout
  *
  * Call writepages on the mapping using the provided wbc to control the
  * writeout.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int filemap_fdatawrite_wbc(struct address_space *mapping,
                struct writeback_control *wbc)
 {
     int ret;
 
     if (!mapping_can_writeback(mapping) ||
         !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
         return 0;
 
     wbc_attach_fdatawrite_inode(wbc, mapping->host);
     ret = do_writepages(mapping, wbc);
     wbc_detach_inode(wbc);
     return ret;
 }
 EXPORT_SYMBOL(filemap_fdatawrite_wbc);
 
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:    address space structure to write
  * @start:  offset in bytes where the range starts
  * @end:    offset in bytes where the range ends (inclusive)
  * @sync_mode:  enable synchronous operation
  *
  * Start writeback against all of a mapping's dirty pages that lie
  * within the byte offsets <start, end> inclusive.
  *
  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
  * opposed to a regular memory cleansing writeback.  The difference between
  * these two operations is that if a dirty page/buffer is encountered, it must
  * be waited upon, and not just skipped over.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
                 loff_t end, int sync_mode)
 {
     struct writeback_control wbc = {
         .sync_mode = sync_mode,
         .nr_to_write = LONG_MAX,
         .range_start = start,
         .range_end = end,
     };
 
     return filemap_fdatawrite_wbc(mapping, &wbc);
 }
 
 static inline int __filemap_fdatawrite(struct address_space *mapping,
     int sync_mode)
 {
     return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
 }
 
 int filemap_fdatawrite(struct address_space *mapping)
 {
     return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
 }
 EXPORT_SYMBOL(filemap_fdatawrite);
 
 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
                 loff_t end)
 {
     return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
 }
 EXPORT_SYMBOL(filemap_fdatawrite_range);
 
 /**
  * filemap_flush - mostly a non-blocking flush
  * @mapping:    target address_space
  *
  * This is a mostly non-blocking flush.  Not suitable for data-integrity
  * purposes - I/O may not be started against all dirty pages.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int filemap_flush(struct address_space *mapping)
 {
     return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
 }
 EXPORT_SYMBOL(filemap_flush);
 
 /**
  * filemap_range_has_page - check if a page exists in range.
  * @mapping:           address space within which to check
  * @start_byte:        offset in bytes where the range starts
  * @end_byte:          offset in bytes where the range ends (inclusive)
  *
  * Find at least one page in the range supplied, usually used to check if
  * direct writing in this range will trigger a writeback.
  *
  * Return: %true if at least one page exists in the specified range,
  * %false otherwise.
  */
 bool filemap_range_has_page(struct address_space *mapping,
                loff_t start_byte, loff_t end_byte)
 {
     struct page *page;
     XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
     pgoff_t max = end_byte >> PAGE_SHIFT;
 
     if (end_byte < start_byte)
         return false;
 
     rcu_read_lock();
     for (;;) {
         page = xas_find(&xas, max);
         if (xas_retry(&xas, page))
             continue;
         /* Shadow entries don't count */
         if (xa_is_value(page))
             continue;
         /*
          * We don't need to try to pin this page; we're about to
          * release the RCU lock anyway.  It is enough to know that
          * there was a page here recently.
          */
         break;
     }
     rcu_read_unlock();
 
     return page != NULL;
 }
 EXPORT_SYMBOL(filemap_range_has_page);
 
 static void __filemap_fdatawait_range(struct address_space *mapping,
                      loff_t start_byte, loff_t end_byte)
 {
     pgoff_t index = start_byte >> PAGE_SHIFT;
     pgoff_t end = end_byte >> PAGE_SHIFT;
     struct pagevec pvec;
     int nr_pages;
 
     if (end_byte < start_byte)
         return;
 
     pagevec_init(&pvec);
     while (index <= end) {
         unsigned i;
 
         nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
                 end, PAGECACHE_TAG_WRITEBACK);
         if (!nr_pages)
             break;
 
         for (i = 0; i < nr_pages; i++) {
             struct page *page = pvec.pages[i];
 
             wait_on_page_writeback(page);
             ClearPageError(page);
         }
         pagevec_release(&pvec);
         cond_resched();
     }
 }
 
 /**
  * filemap_fdatawait_range - wait for writeback to complete
  * @mapping:        address space structure to wait for
  * @start_byte:     offset in bytes where the range starts
  * @end_byte:       offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the given address space
  * in the given range and wait for all of them.  Check error status of
  * the address space and return it.
  *
  * Since the error status of the address space is cleared by this function,
  * callers are responsible for checking the return value and handling and/or
  * reporting the error.
  *
  * Return: error status of the address space.
  */
 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
                 loff_t end_byte)
 {
     __filemap_fdatawait_range(mapping, start_byte, end_byte);
     return filemap_check_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range);
 
 /**
  * filemap_fdatawait_range_keep_errors - wait for writeback to complete
  * @mapping:        address space structure to wait for
  * @start_byte:     offset in bytes where the range starts
  * @end_byte:       offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the given address space in the
  * given range and wait for all of them.  Unlike filemap_fdatawait_range(),
  * this function does not clear error status of the address space.
  *
  * Use this function if callers don't handle errors themselves.  Expected
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  */
 int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
         loff_t start_byte, loff_t end_byte)
 {
     __filemap_fdatawait_range(mapping, start_byte, end_byte);
     return filemap_check_and_keep_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors);
 
 /**
  * file_fdatawait_range - wait for writeback to complete
  * @file:       file pointing to address space structure to wait for
  * @start_byte:     offset in bytes where the range starts
  * @end_byte:       offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the address space that file
  * refers to, in the given range and wait for all of them.  Check error
  * status of the address space vs. the file->f_wb_err cursor and return it.
  *
  * Since the error status of the file is advanced by this function,
  * callers are responsible for checking the return value and handling and/or
  * reporting the error.
  *
  * Return: error status of the address space vs. the file->f_wb_err cursor.
  */
 int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
 {
     struct address_space *mapping = file->f_mapping;
 
     __filemap_fdatawait_range(mapping, start_byte, end_byte);
     return file_check_and_advance_wb_err(file);
 }
 EXPORT_SYMBOL(file_fdatawait_range);
 
 /**
  * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
  * @mapping: address space structure to wait for
  *
  * Walk the list of under-writeback pages of the given address space
  * and wait for all of them.  Unlike filemap_fdatawait(), this function
  * does not clear error status of the address space.
  *
  * Use this function if callers don't handle errors themselves.  Expected
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  *
  * Return: error status of the address space.
  */
 int filemap_fdatawait_keep_errors(struct address_space *mapping)
 {
     __filemap_fdatawait_range(mapping, 0, LLONG_MAX);
     return filemap_check_and_keep_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
 /* Returns true if writeback might be needed or already in progress. */
 static bool mapping_needs_writeback(struct address_space *mapping)
 {
     return mapping->nrpages;
 }
 
 bool filemap_range_has_writeback(struct address_space *mapping,
                  loff_t start_byte, loff_t end_byte)
 {
     XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
     pgoff_t max = end_byte >> PAGE_SHIFT;
     struct page *page;
 
     if (end_byte < start_byte)
         return false;
 
     rcu_read_lock();
     xas_for_each(&xas, page, max) {
         if (xas_retry(&xas, page))
             continue;
         if (xa_is_value(page))
             continue;
         if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
             break;
     }
     rcu_read_unlock();
     return page != NULL;
 }
 EXPORT_SYMBOL_GPL(filemap_range_has_writeback);
 
 /**
  * filemap_write_and_wait_range - write out & wait on a file range
  * @mapping:    the address_space for the pages
  * @lstart: offset in bytes where the range starts
  * @lend:   offset in bytes where the range ends (inclusive)
  *
  * Write out and wait upon file offsets lstart->lend, inclusive.
  *
  * Note that @lend is inclusive (describes the last byte to be written) so
  * that this function can be used to write to the very end-of-file (end = -1).
  *
  * Return: error status of the address space.
  */
 int filemap_write_and_wait_range(struct address_space *mapping,
                  loff_t lstart, loff_t lend)
 {
     int err = 0, err2;
 
     if (mapping_needs_writeback(mapping)) {
         err = __filemap_fdatawrite_range(mapping, lstart, lend,
                          WB_SYNC_ALL);
         /*
          * Even if the above returned error, the pages may be
          * written partially (e.g. -ENOSPC), so we wait for it.
          * But the -EIO is special case, it may indicate the worst
          * thing (e.g. bug) happened, so we avoid waiting for it.
          */
         if (err != -EIO)
             __filemap_fdatawait_range(mapping, lstart, lend);
     }
     err2 = filemap_check_errors(mapping);
     if (!err)
         err = err2;
     return err;
 }
 EXPORT_SYMBOL(filemap_write_and_wait_range);
 
 void __filemap_set_wb_err(struct address_space *mapping, int err)
 {
     errseq_t eseq = errseq_set(&mapping->wb_err, err);
 
     trace_filemap_set_wb_err(mapping, eseq);
 }
 EXPORT_SYMBOL(__filemap_set_wb_err);
 
 /**
  * file_check_and_advance_wb_err - report wb error (if any) that was previously
  *                 and advance wb_err to current one
  * @file: struct file on which the error is being reported
  *
  * When userland calls fsync (or something like nfsd does the equivalent), we
  * want to report any writeback errors that occurred since the last fsync (or
  * since the file was opened if there haven't been any).
  *
  * Grab the wb_err from the mapping. If it matches what we have in the file,
  * then just quickly return 0. The file is all caught up.
  *
  * If it doesn't match, then take the mapping value, set the "seen" flag in
  * it and try to swap it into place. If it works, or another task beat us
  * to it with the new value, then update the f_wb_err and return the error
  * portion. The error at this point must be reported via proper channels
  * (a'la fsync, or NFS COMMIT operation, etc.).
  *
  * While we handle mapping->wb_err with atomic operations, the f_wb_err
  * value is protected by the f_lock since we must ensure that it reflects
  * the latest value swapped in for this file descriptor.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int file_check_and_advance_wb_err(struct file *file)
 {
     int err = 0;
     errseq_t old = READ_ONCE(file->f_wb_err);
     struct address_space *mapping = file->f_mapping;
 
     /* Locklessly handle the common case where nothing has changed */
     if (errseq_check(&mapping->wb_err, old)) {
         /* Something changed, must use slow path */
         spin_lock(&file->f_lock);
         old = file->f_wb_err;
         err = errseq_check_and_advance(&mapping->wb_err,
                         &file->f_wb_err);
         trace_file_check_and_advance_wb_err(file, old);
         spin_unlock(&file->f_lock);
     }
 
     /*
      * We're mostly using this function as a drop in replacement for
      * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
      * that the legacy code would have had on these flags.
      */
     clear_bit(AS_EIO, &mapping->flags);
     clear_bit(AS_ENOSPC, &mapping->flags);
     return err;
 }
 EXPORT_SYMBOL(file_check_and_advance_wb_err);
 
 /**
  * file_write_and_wait_range - write out & wait on a file range
  * @file:   file pointing to address_space with pages
  * @lstart: offset in bytes where the range starts
  * @lend:   offset in bytes where the range ends (inclusive)
  *
  * Write out and wait upon file offsets lstart->lend, inclusive.
  *
  * Note that @lend is inclusive (describes the last byte to be written) so
  * that this function can be used to write to the very end-of-file (end = -1).
  *
  * After writing out and waiting on the data, we check and advance the
  * f_wb_err cursor to the latest value, and return any errors detected there.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
 {
     int err = 0, err2;
     struct address_space *mapping = file->f_mapping;
 
     if (mapping_needs_writeback(mapping)) {
         err = __filemap_fdatawrite_range(mapping, lstart, lend,
                          WB_SYNC_ALL);
         /* See comment of filemap_write_and_wait() */
         if (err != -EIO)
             __filemap_fdatawait_range(mapping, lstart, lend);
     }
     err2 = file_check_and_advance_wb_err(file);
     if (!err)
         err = err2;
     return err;
 }
 EXPORT_SYMBOL(file_write_and_wait_range);
 
 /**
  * replace_page_cache_page - replace a pagecache page with a new one
  * @old:    page to be replaced
  * @new:    page to replace with
  *
  * This function replaces a page in the pagecache with a new one.  On
  * success it acquires the pagecache reference for the new page and
  * drops it for the old page.  Both the old and new pages must be
  * locked.  This function does not add the new page to the LRU, the
  * caller must do that.
  *
  * The remove + add is atomic.  This function cannot fail.
  */
 void replace_page_cache_page(struct page *old, struct page *new)
 {
     struct folio *fold = page_folio(old);
     struct folio *fnew = page_folio(new);
     struct address_space *mapping = old->mapping;
     void (*free_folio)(struct folio *) = mapping->a_ops->free_folio;
     pgoff_t offset = old->index;
     XA_STATE(xas, &mapping->i_pages, offset);
 
     VM_BUG_ON_PAGE(!PageLocked(old), old);
     VM_BUG_ON_PAGE(!PageLocked(new), new);
     VM_BUG_ON_PAGE(new->mapping, new);
 
     get_page(new);
     new->mapping = mapping;
     new->index = offset;
 
     mem_cgroup_migrate(fold, fnew);
 
     xas_lock_irq(&xas);
     xas_store(&xas, new);
 
     old->mapping = NULL;
     /* hugetlb pages do not participate in page cache accounting. */
     if (!PageHuge(old))
         __dec_lruvec_page_state(old, NR_FILE_PAGES);
     if (!PageHuge(new))
         __inc_lruvec_page_state(new, NR_FILE_PAGES);
     if (PageSwapBacked(old))
         __dec_lruvec_page_state(old, NR_SHMEM);
     if (PageSwapBacked(new))
         __inc_lruvec_page_state(new, NR_SHMEM);
     xas_unlock_irq(&xas);
     if (free_folio)
         free_folio(fold);
     folio_put(fold);
 }
 EXPORT_SYMBOL_GPL(replace_page_cache_page);
 
 noinline int __filemap_add_folio(struct address_space *mapping,
         struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
 {
     XA_STATE(xas, &mapping->i_pages, index);
     int huge = folio_test_hugetlb(folio);
     bool charged = false;
     long nr = 1;
 
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
     VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
     mapping_set_update(&xas, mapping);
 
     if (!huge) {
         int error = mem_cgroup_charge(folio, NULL, gfp);
         VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
         if (error)
             return error;
         charged = true;
         xas_set_order(&xas, index, folio_order(folio));
         nr = folio_nr_pages(folio);
     }
 
     gfp &= GFP_RECLAIM_MASK;
     folio_ref_add(folio, nr);
     folio->mapping = mapping;
     folio->index = xas.xa_index;
 
     do {
         unsigned int order = xa_get_order(xas.xa, xas.xa_index);
         void *entry, *old = NULL;
 
         if (order > folio_order(folio))
             xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index),
                     order, gfp);
         xas_lock_irq(&xas);
         xas_for_each_conflict(&xas, entry) {
             old = entry;
             if (!xa_is_value(entry)) {
                 xas_set_err(&xas, -EEXIST);
                 goto unlock;
             }
         }
 
         if (old) {
             if (shadowp)
                 *shadowp = old;
             /* entry may have been split before we acquired lock */
             order = xa_get_order(xas.xa, xas.xa_index);
             if (order > folio_order(folio)) {
                 /* How to handle large swap entries? */
                 BUG_ON(shmem_mapping(mapping));
                 xas_split(&xas, old, order);
                 xas_reset(&xas);
             }
         }
 
         xas_store(&xas, folio);
         if (xas_error(&xas))
             goto unlock;
 
         mapping->nrpages += nr;
 
         /* hugetlb pages do not participate in page cache accounting */
         if (!huge) {
             __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr);
             if (folio_test_pmd_mappable(folio))
                 __lruvec_stat_mod_folio(folio,
                         NR_FILE_THPS, nr);
         }
 unlock:
         xas_unlock_irq(&xas);
     } while (xas_nomem(&xas, gfp));
 
     if (xas_error(&xas))
         goto error;
 
     trace_mm_filemap_add_to_page_cache(folio);
     return 0;
 error:
     if (charged)
         mem_cgroup_uncharge(folio);
     folio->mapping = NULL;
     /* Leave page->index set: truncation relies upon it */
     folio_put_refs(folio, nr);
     return xas_error(&xas);
 }
 ALLOW_ERROR_INJECTION(__filemap_add_folio, ERRNO);
 
 int filemap_add_folio(struct address_space *mapping, struct folio *folio,
                 pgoff_t index, gfp_t gfp)
 {
     void *shadow = NULL;
     int ret;
 
     __folio_set_locked(folio);
     ret = __filemap_add_folio(mapping, folio, index, gfp, &shadow);
     if (unlikely(ret))
         __folio_clear_locked(folio);
     else {
         /*
          * The folio might have been evicted from cache only
          * recently, in which case it should be activated like
          * any other repeatedly accessed folio.
          * The exception is folios getting rewritten; evicting other
          * data from the working set, only to cache data that will
          * get overwritten with something else, is a waste of memory.
          */
         WARN_ON_ONCE(folio_test_active(folio));
         if (!(gfp & __GFP_WRITE) && shadow)
             workingset_refault(folio, shadow);
         folio_add_lru(folio);
     }
     return ret;
 }
 EXPORT_SYMBOL_GPL(filemap_add_folio);
 
 #ifdef CONFIG_NUMA
 struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order)
 {
     int n;
     struct folio *folio;
 
     if (cpuset_do_page_mem_spread()) {
         unsigned int cpuset_mems_cookie;
         do {
             cpuset_mems_cookie = read_mems_allowed_begin();
             n = cpuset_mem_spread_node();
             folio = __folio_alloc_node(gfp, order, n);
         } while (!folio && read_mems_allowed_retry(cpuset_mems_cookie));
 
         return folio;
     }
     return folio_alloc(gfp, order);
 }
 EXPORT_SYMBOL(filemap_alloc_folio);
 #endif
 
 /*
  * filemap_invalidate_lock_two - lock invalidate_lock for two mappings
  *
  * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
  *
  * @mapping1: the first mapping to lock
  * @mapping2: the second mapping to lock
  */
 void filemap_invalidate_lock_two(struct address_space *mapping1,
                  struct address_space *mapping2)
 {
     if (mapping1 > mapping2)
         swap(mapping1, mapping2);
     if (mapping1)
         down_write(&mapping1->invalidate_lock);
     if (mapping2 && mapping1 != mapping2)
         down_write_nested(&mapping2->invalidate_lock, 1);
 }
 EXPORT_SYMBOL(filemap_invalidate_lock_two);
 
 /*
  * filemap_invalidate_unlock_two - unlock invalidate_lock for two mappings
  *
  * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
  *
  * @mapping1: the first mapping to unlock
  * @mapping2: the second mapping to unlock
  */
 void filemap_invalidate_unlock_two(struct address_space *mapping1,
                    struct address_space *mapping2)
 {
     if (mapping1)
         up_write(&mapping1->invalidate_lock);
     if (mapping2 && mapping1 != mapping2)
         up_write(&mapping2->invalidate_lock);
 }
 EXPORT_SYMBOL(filemap_invalidate_unlock_two);
 
 /*
  * In order to wait for pages to become available there must be
  * waitqueues associated with pages. By using a hash table of
  * waitqueues where the bucket discipline is to maintain all
  * waiters on the same queue and wake all when any of the pages
  * become available, and for the woken contexts to check to be
  * sure the appropriate page became available, this saves space
  * at a cost of "thundering herd" phenomena during rare hash
  * collisions.
  */
 #define PAGE_WAIT_TABLE_BITS 8
 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
 static wait_queue_head_t folio_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
 
 static wait_queue_head_t *folio_waitqueue(struct folio *folio)
 {
     return &folio_wait_table[hash_ptr(folio, PAGE_WAIT_TABLE_BITS)];
 }
 
 void __init pagecache_init(void)
 {
     int i;
 
     for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
         init_waitqueue_head(&folio_wait_table[i]);
 
     page_writeback_init();
 }
 
 /*
  * The page wait code treats the "wait->flags" somewhat unusually, because
  * we have multiple different kinds of waits, not just the usual "exclusive"
  * one.
  *
  * We have:
  *
  *  (a) no special bits set:
  *
  *  We're just waiting for the bit to be released, and when a waker
  *  calls the wakeup function, we set WQ_FLAG_WOKEN and wake it up,
  *  and remove it from the wait queue.
  *
  *  Simple and straightforward.
  *
  *  (b) WQ_FLAG_EXCLUSIVE:
  *
  *  The waiter is waiting to get the lock, and only one waiter should
  *  be woken up to avoid any thundering herd behavior. We'll set the
  *  WQ_FLAG_WOKEN bit, wake it up, and remove it from the wait queue.
  *
  *  This is the traditional exclusive wait.
  *
  *  (c) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM:
  *
  *  The waiter is waiting to get the bit, and additionally wants the
  *  lock to be transferred to it for fair lock behavior. If the lock
  *  cannot be taken, we stop walking the wait queue without waking
  *  the waiter.
  *
  *  This is the "fair lock handoff" case, and in addition to setting
  *  WQ_FLAG_WOKEN, we set WQ_FLAG_DONE to let the waiter easily see
  *  that it now has the lock.
  */
 static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
 {
     unsigned int flags;
     struct wait_page_key *key = arg;
     struct wait_page_queue *wait_page
         = container_of(wait, struct wait_page_queue, wait);
 
     if (!wake_page_match(wait_page, key))
         return 0;
 
     /*
      * If it's a lock handoff wait, we get the bit for it, and
      * stop walking (and do not wake it up) if we can't.
      */
     flags = wait->flags;
     if (flags & WQ_FLAG_EXCLUSIVE) {
         if (test_bit(key->bit_nr, &key->folio->flags))
             return -1;
         if (flags & WQ_FLAG_CUSTOM) {
             if (test_and_set_bit(key->bit_nr, &key->folio->flags))
                 return -1;
             flags |= WQ_FLAG_DONE;
         }
     }
 
     /*
      * We are holding the wait-queue lock, but the waiter that
      * is waiting for this will be checking the flags without
      * any locking.
      *
      * So update the flags atomically, and wake up the waiter
      * afterwards to avoid any races. This store-release pairs
      * with the load-acquire in folio_wait_bit_common().
      */
     smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
     wake_up_state(wait->private, mode);
 
     /*
      * Ok, we have successfully done what we're waiting for,
      * and we can unconditionally remove the wait entry.
      *
      * Note that this pairs with the "finish_wait()" in the
      * waiter, and has to be the absolute last thing we do.
      * After this list_del_init(&wait->entry) the wait entry
      * might be de-allocated and the process might even have
      * exited.
      */
     list_del_init_careful(&wait->entry);
     return (flags & WQ_FLAG_EXCLUSIVE) != 0;
 }
 
 static void folio_wake_bit(struct folio *folio, int bit_nr)
 {
     wait_queue_head_t *q = folio_waitqueue(folio);
     struct wait_page_key key;
     unsigned long flags;
     wait_queue_entry_t bookmark;
 
     key.folio = folio;
     key.bit_nr = bit_nr;
     key.page_match = 0;
 
     bookmark.flags = 0;
     bookmark.private = NULL;
     bookmark.func = NULL;
     INIT_LIST_HEAD(&bookmark.entry);
 
     spin_lock_irqsave(&q->lock, flags);
     __wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
 
     while (bookmark.flags & WQ_FLAG_BOOKMARK) {
         /*
          * Take a breather from holding the lock,
          * allow pages that finish wake up asynchronously
          * to acquire the lock and remove themselves
          * from wait queue
          */
         spin_unlock_irqrestore(&q->lock, flags);
         cpu_relax();
         spin_lock_irqsave(&q->lock, flags);
         __wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
     }
 
     /*
      * It's possible to miss clearing waiters here, when we woke our page
      * waiters, but the hashed waitqueue has waiters for other pages on it.
      * That's okay, it's a rare case. The next waker will clear it.
      *
      * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE,
      * other), the flag may be cleared in the course of freeing the page;
      * but that is not required for correctness.
      */
     if (!waitqueue_active(q) || !key.page_match)
         folio_clear_waiters(folio);
 
     spin_unlock_irqrestore(&q->lock, flags);
 }
 
 static void folio_wake(struct folio *folio, int bit)
 {
     if (!folio_test_waiters(folio))
         return;
     folio_wake_bit(folio, bit);
 }
 
 /*
  * A choice of three behaviors for folio_wait_bit_common():
  */
 enum behavior {
     EXCLUSIVE,  /* Hold ref to page and take the bit when woken, like
              * __folio_lock() waiting on then setting PG_locked.
              */
     SHARED,     /* Hold ref to page and check the bit when woken, like
              * folio_wait_writeback() waiting on PG_writeback.
              */
     DROP,       /* Drop ref to page before wait, no check when woken,
              * like folio_put_wait_locked() on PG_locked.
              */
 };
 
 /*
  * Attempt to check (or get) the folio flag, and mark us done
  * if successful.
  */
 static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
                     struct wait_queue_entry *wait)
 {
     if (wait->flags & WQ_FLAG_EXCLUSIVE) {
         if (test_and_set_bit(bit_nr, &folio->flags))
             return false;
     } else if (test_bit(bit_nr, &folio->flags))
         return false;
 
     wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
     return true;
 }
 
 /* How many times do we accept lock stealing from under a waiter? */
 int sysctl_page_lock_unfairness = 5;
 
 static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
         int state, enum behavior behavior)
 {
     wait_queue_head_t *q = folio_waitqueue(folio);
     int unfairness = sysctl_page_lock_unfairness;
     struct wait_page_queue wait_page;
     wait_queue_entry_t *wait = &wait_page.wait;
     bool thrashing = false;
     bool delayacct = false;
     unsigned long pflags;
 
     if (bit_nr == PG_locked &&
         !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
         if (!folio_test_swapbacked(folio)) {
             delayacct_thrashing_start();
             delayacct = true;
         }
         psi_memstall_enter(&pflags);
         thrashing = true;
     }
 
     init_wait(wait);
     wait->func = wake_page_function;
     wait_page.folio = folio;
     wait_page.bit_nr = bit_nr;
 
 repeat:
     wait->flags = 0;
     if (behavior == EXCLUSIVE) {
         wait->flags = WQ_FLAG_EXCLUSIVE;
         if (--unfairness < 0)
             wait->flags |= WQ_FLAG_CUSTOM;
     }
 
     /*
      * Do one last check whether we can get the
      * page bit synchronously.
      *
      * Do the folio_set_waiters() marking before that
      * to let any waker we _just_ missed know they
      * need to wake us up (otherwise they'll never
      * even go to the slow case that looks at the
      * page queue), and add ourselves to the wait
      * queue if we need to sleep.
      *
      * This part needs to be done under the queue
      * lock to avoid races.
      */
     spin_lock_irq(&q->lock);
     folio_set_waiters(folio);
     if (!folio_trylock_flag(folio, bit_nr, wait))
         __add_wait_queue_entry_tail(q, wait);
     spin_unlock_irq(&q->lock);
 
     /*
      * From now on, all the logic will be based on
      * the WQ_FLAG_WOKEN and WQ_FLAG_DONE flag, to
      * see whether the page bit testing has already
      * been done by the wake function.
      *
      * We can drop our reference to the folio.
      */
     if (behavior == DROP)
         folio_put(folio);
 
     /*
      * Note that until the "finish_wait()", or until
      * we see the WQ_FLAG_WOKEN flag, we need to
      * be very careful with the 'wait->flags', because
      * we may race with a waker that sets them.
      */
     for (;;) {
         unsigned int flags;
 
         set_current_state(state);
 
         /* Loop until we've been woken or interrupted */
         flags = smp_load_acquire(&wait->flags);
         if (!(flags & WQ_FLAG_WOKEN)) {
             if (signal_pending_state(state, current))
                 break;
 
             io_schedule();
             continue;
         }
 
         /* If we were non-exclusive, we're done */
         if (behavior != EXCLUSIVE)
             break;
 
         /* If the waker got the lock for us, we're done */
         if (flags & WQ_FLAG_DONE)
             break;
 
         /*
          * Otherwise, if we're getting the lock, we need to
          * try to get it ourselves.
          *
          * And if that fails, we'll have to retry this all.
          */
         if (unlikely(test_and_set_bit(bit_nr, folio_flags(folio, 0))))
             goto repeat;
 
         wait->flags |= WQ_FLAG_DONE;
         break;
     }
 
     /*
      * If a signal happened, this 'finish_wait()' may remove the last
      * waiter from the wait-queues, but the folio waiters bit will remain
      * set. That's ok. The next wakeup will take care of it, and trying
      * to do it here would be difficult and prone to races.
      */
     finish_wait(q, wait);
 
     if (thrashing) {
         if (delayacct)
             delayacct_thrashing_end();
         psi_memstall_leave(&pflags);
     }
 
     /*
      * NOTE! The wait->flags weren't stable until we've done the
      * 'finish_wait()', and we could have exited the loop above due
      * to a signal, and had a wakeup event happen after the signal
      * test but before the 'finish_wait()'.
      *
      * So only after the finish_wait() can we reliably determine
      * if we got woken up or not, so we can now figure out the final
      * return value based on that state without races.
      *
      * Also note that WQ_FLAG_WOKEN is sufficient for a non-exclusive
      * waiter, but an exclusive one requires WQ_FLAG_DONE.
      */
     if (behavior == EXCLUSIVE)
         return wait->flags & WQ_FLAG_DONE ? 0 : -EINTR;
 
     return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
 }
 
 #ifdef CONFIG_MIGRATION
 /**
  * migration_entry_wait_on_locked - Wait for a migration entry to be removed
  * @entry: migration swap entry.
  * @ptep: mapped pte pointer. Will return with the ptep unmapped. Only required
  *        for pte entries, pass NULL for pmd entries.
  * @ptl: already locked ptl. This function will drop the lock.
  *
  * Wait for a migration entry referencing the given page to be removed. This is
  * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
  * this can be called without taking a reference on the page. Instead this
  * should be called while holding the ptl for the migration entry referencing
  * the page.
  *
  * Returns after unmapping and unlocking the pte/ptl with pte_unmap_unlock().
  *
  * This follows the same logic as folio_wait_bit_common() so see the comments
  * there.
  */
 void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
                 spinlock_t *ptl)
 {
     struct wait_page_queue wait_page;
     wait_queue_entry_t *wait = &wait_page.wait;
     bool thrashing = false;
     bool delayacct = false;
     unsigned long pflags;
     wait_queue_head_t *q;
     struct folio *folio = page_folio(pfn_swap_entry_to_page(entry));
 
     q = folio_waitqueue(folio);
     if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
         if (!folio_test_swapbacked(folio)) {
             delayacct_thrashing_start();
             delayacct = true;
         }
         psi_memstall_enter(&pflags);
         thrashing = true;
     }
 
     init_wait(wait);
     wait->func = wake_page_function;
     wait_page.folio = folio;
     wait_page.bit_nr = PG_locked;
     wait->flags = 0;
 
     spin_lock_irq(&q->lock);
     folio_set_waiters(folio);
     if (!folio_trylock_flag(folio, PG_locked, wait))
         __add_wait_queue_entry_tail(q, wait);
     spin_unlock_irq(&q->lock);
 
     /*
      * If a migration entry exists for the page the migration path must hold
      * a valid reference to the page, and it must take the ptl to remove the
      * migration entry. So the page is valid until the ptl is dropped.
      */
     if (ptep)
         pte_unmap_unlock(ptep, ptl);
     else
         spin_unlock(ptl);
 
     for (;;) {
         unsigned int flags;
 
         set_current_state(TASK_UNINTERRUPTIBLE);
 
         /* Loop until we've been woken or interrupted */
         flags = smp_load_acquire(&wait->flags);
         if (!(flags & WQ_FLAG_WOKEN)) {
             if (signal_pending_state(TASK_UNINTERRUPTIBLE, current))
                 break;
 
             io_schedule();
             continue;
         }
         break;
     }
 
     finish_wait(q, wait);
 
     if (thrashing) {
         if (delayacct)
             delayacct_thrashing_end();
         psi_memstall_leave(&pflags);
     }
 }
 #endif
 
 void folio_wait_bit(struct folio *folio, int bit_nr)
 {
     folio_wait_bit_common(folio, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
 }
 EXPORT_SYMBOL(folio_wait_bit);
 
 int folio_wait_bit_killable(struct folio *folio, int bit_nr)
 {
     return folio_wait_bit_common(folio, bit_nr, TASK_KILLABLE, SHARED);
 }
 EXPORT_SYMBOL(folio_wait_bit_killable);
 
 /**
  * folio_put_wait_locked - Drop a reference and wait for it to be unlocked
  * @folio: The folio to wait for.
  * @state: The sleep state (TASK_KILLABLE, TASK_UNINTERRUPTIBLE, etc).
  *
  * The caller should hold a reference on @folio.  They expect the page to
  * become unlocked relatively soon, but do not wish to hold up migration
  * (for example) by holding the reference while waiting for the folio to
  * come unlocked.  After this function returns, the caller should not
  * dereference @folio.
  *
  * Return: 0 if the folio was unlocked or -EINTR if interrupted by a signal.
  */
 int folio_put_wait_locked(struct folio *folio, int state)
 {
     return folio_wait_bit_common(folio, PG_locked, state, DROP);
 }
 
 /**
  * folio_add_wait_queue - Add an arbitrary waiter to a folio's wait queue
  * @folio: Folio defining the wait queue of interest
  * @waiter: Waiter to add to the queue
  *
  * Add an arbitrary @waiter to the wait queue for the nominated @folio.
  */
 void folio_add_wait_queue(struct folio *folio, wait_queue_entry_t *waiter)
 {
     wait_queue_head_t *q = folio_waitqueue(folio);
     unsigned long flags;
 
     spin_lock_irqsave(&q->lock, flags);
     __add_wait_queue_entry_tail(q, waiter);
     folio_set_waiters(folio);
     spin_unlock_irqrestore(&q->lock, flags);
 }
 EXPORT_SYMBOL_GPL(folio_add_wait_queue);
 
 #ifndef clear_bit_unlock_is_negative_byte
 
 /*
  * PG_waiters is the high bit in the same byte as PG_lock.
  *
  * On x86 (and on many other architectures), we can clear PG_lock and
  * test the sign bit at the same time. But if the architecture does
  * not support that special operation, we just do this all by hand
  * instead.
  *
  * The read of PG_waiters has to be after (or concurrently with) PG_locked
  * being cleared, but a memory barrier should be unnecessary since it is
  * in the same byte as PG_locked.
  */
 static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
 {
     clear_bit_unlock(nr, mem);
     /* smp_mb__after_atomic(); */
     return test_bit(PG_waiters, mem);
 }
 
 #endif
 
 /**
  * folio_unlock - Unlock a locked folio.
  * @folio: The folio.
  *
  * Unlocks the folio and wakes up any thread sleeping on the page lock.
  *
  * Context: May be called from interrupt or process context.  May not be
  * called from NMI context.
  */
 void folio_unlock(struct folio *folio)
 {
     /* Bit 7 allows x86 to check the byte's sign bit */
     BUILD_BUG_ON(PG_waiters != 7);
     BUILD_BUG_ON(PG_locked > 7);
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
     if (clear_bit_unlock_is_negative_byte(PG_locked, folio_flags(folio, 0)))
         folio_wake_bit(folio, PG_locked);
 }
 EXPORT_SYMBOL(folio_unlock);
 
 /**
  * folio_end_private_2 - Clear PG_private_2 and wake any waiters.
  * @folio: The folio.
  *
  * Clear the PG_private_2 bit on a folio and wake up any sleepers waiting for
  * it.  The folio reference held for PG_private_2 being set is released.
  *
  * This is, for example, used when a netfs folio is being written to a local
  * disk cache, thereby allowing writes to the cache for the same folio to be
  * serialised.
  */
 void folio_end_private_2(struct folio *folio)
 {
     VM_BUG_ON_FOLIO(!folio_test_private_2(folio), folio);
     clear_bit_unlock(PG_private_2, folio_flags(folio, 0));
     folio_wake_bit(folio, PG_private_2);
     folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_private_2);
 
 /**
  * folio_wait_private_2 - Wait for PG_private_2 to be cleared on a folio.
  * @folio: The folio to wait on.
  *
  * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio.
  */
 void folio_wait_private_2(struct folio *folio)
 {
     while (folio_test_private_2(folio))
         folio_wait_bit(folio, PG_private_2);
 }
 EXPORT_SYMBOL(folio_wait_private_2);
 
 /**
  * folio_wait_private_2_killable - Wait for PG_private_2 to be cleared on a folio.
  * @folio: The folio to wait on.
  *
  * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio or until a
  * fatal signal is received by the calling task.
  *
  * Return:
  * - 0 if successful.
  * - -EINTR if a fatal signal was encountered.
  */
 int folio_wait_private_2_killable(struct folio *folio)
 {
     int ret = 0;
 
     while (folio_test_private_2(folio)) {
         ret = folio_wait_bit_killable(folio, PG_private_2);
         if (ret < 0)
             break;
     }
 
     return ret;
 }
 EXPORT_SYMBOL(folio_wait_private_2_killable);
 
 /**
  * folio_end_writeback - End writeback against a folio.
  * @folio: The folio.
  */
 void folio_end_writeback(struct folio *folio)
 {
     /*
      * folio_test_clear_reclaim() could be used here but it is an
      * atomic operation and overkill in this particular case. Failing
      * to shuffle a folio marked for immediate reclaim is too mild
      * a gain to justify taking an atomic operation penalty at the
      * end of every folio writeback.
      */
     if (folio_test_reclaim(folio)) {
         folio_clear_reclaim(folio);
         folio_rotate_reclaimable(folio);
     }
 
     /*
      * Writeback does not hold a folio reference of its own, relying
      * on truncation to wait for the clearing of PG_writeback.
      * But here we must make sure that the folio is not freed and
      * reused before the folio_wake().
      */
     folio_get(folio);
     if (!__folio_end_writeback(folio))
         BUG();
 
     smp_mb__after_atomic();
     folio_wake(folio, PG_writeback);
     acct_reclaim_writeback(folio);
     folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_writeback);
 
 /*
  * After completing I/O on a page, call this routine to update the page
  * flags appropriately
  */
 void page_endio(struct page *page, bool is_write, int err)
 {
     if (!is_write) {
         if (!err) {
             SetPageUptodate(page);
         } else {
             ClearPageUptodate(page);
             SetPageError(page);
         }
         unlock_page(page);
     } else {
         if (err) {
             struct address_space *mapping;
 
             SetPageError(page);
             mapping = page_mapping(page);
             if (mapping)
                 mapping_set_error(mapping, err);
         }
         end_page_writeback(page);
     }
 }
 EXPORT_SYMBOL_GPL(page_endio);
 
 /**
  * __folio_lock - Get a lock on the folio, assuming we need to sleep to get it.
  * @folio: The folio to lock
  */
 void __folio_lock(struct folio *folio)
 {
     folio_wait_bit_common(folio, PG_locked, TASK_UNINTERRUPTIBLE,
                 EXCLUSIVE);
 }
 EXPORT_SYMBOL(__folio_lock);
 
 int __folio_lock_killable(struct folio *folio)
 {
     return folio_wait_bit_common(folio, PG_locked, TASK_KILLABLE,
                     EXCLUSIVE);
 }
 EXPORT_SYMBOL_GPL(__folio_lock_killable);
 
 static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
 {
     struct wait_queue_head *q = folio_waitqueue(folio);
     int ret = 0;
 
     wait->folio = folio;
     wait->bit_nr = PG_locked;
 
     spin_lock_irq(&q->lock);
     __add_wait_queue_entry_tail(q, &wait->wait);
     folio_set_waiters(folio);
     ret = !folio_trylock(folio);
     /*
      * If we were successful now, we know we're still on the
      * waitqueue as we're still under the lock. This means it's
      * safe to remove and return success, we know the callback
      * isn't going to trigger.
      */
     if (!ret)
         __remove_wait_queue(q, &wait->wait);
     else
         ret = -EIOCBQUEUED;
     spin_unlock_irq(&q->lock);
     return ret;
 }
 
 /*
  * Return values:
  * true - folio is locked; mmap_lock is still held.
  * false - folio is not locked.
  *     mmap_lock has been released (mmap_read_unlock(), unless flags had both
  *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
  *     which case mmap_lock is still held.
  *
  * If neither ALLOW_RETRY nor KILLABLE are set, will always return true
  * with the folio locked and the mmap_lock unperturbed.
  */
 bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
              unsigned int flags)
 {
     if (fault_flag_allow_retry_first(flags)) {
         /*
          * CAUTION! In this case, mmap_lock is not released
          * even though return 0.
          */
         if (flags & FAULT_FLAG_RETRY_NOWAIT)
             return false;
 
         mmap_read_unlock(mm);
         if (flags & FAULT_FLAG_KILLABLE)
             folio_wait_locked_killable(folio);
         else
             folio_wait_locked(folio);
         return false;
     }
     if (flags & FAULT_FLAG_KILLABLE) {
         bool ret;
 
         ret = __folio_lock_killable(folio);
         if (ret) {
             mmap_read_unlock(mm);
             return false;
         }
     } else {
         __folio_lock(folio);
     }
 
     return true;
 }
 
 /**
  * page_cache_next_miss() - Find the next gap in the page cache.
  * @mapping: Mapping.
  * @index: Index.
  * @max_scan: Maximum range to search.
  *
  * Search the range [index, min(index + max_scan - 1, ULONG_MAX)] for the
  * gap with the lowest index.
  *
  * This function may be called under the rcu_read_lock.  However, this will
  * not atomically search a snapshot of the cache at a single point in time.
  * For example, if a gap is created at index 5, then subsequently a gap is
  * created at index 10, page_cache_next_miss covering both indices may
  * return 10 if called under the rcu_read_lock.
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'return - index >= max_scan' will be true).
  * In the rare case of index wrap-around, 0 will be returned.
  */
 pgoff_t page_cache_next_miss(struct address_space *mapping,
                  pgoff_t index, unsigned long max_scan)
 {
     XA_STATE(xas, &mapping->i_pages, index);
 
     while (max_scan--) {
         void *entry = xas_next(&xas);
         if (!entry || xa_is_value(entry))
             break;
         if (xas.xa_index == 0)
             break;
     }
 
     return xas.xa_index;
 }
 EXPORT_SYMBOL(page_cache_next_miss);
 
 /**
  * page_cache_prev_miss() - Find the previous gap in the page cache.
  * @mapping: Mapping.
  * @index: Index.
  * @max_scan: Maximum range to search.
  *
  * Search the range [max(index - max_scan + 1, 0), index] for the
  * gap with the highest index.
  *
  * This function may be called under the rcu_read_lock.  However, this will
  * not atomically search a snapshot of the cache at a single point in time.
  * For example, if a gap is created at index 10, then subsequently a gap is
  * created at index 5, page_cache_prev_miss() covering both indices may
  * return 5 if called under the rcu_read_lock.
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'index - return >= max_scan' will be true).
  * In the rare case of wrap-around, ULONG_MAX will be returned.
  */
 pgoff_t page_cache_prev_miss(struct address_space *mapping,
                  pgoff_t index, unsigned long max_scan)
 {
     XA_STATE(xas, &mapping->i_pages, index);
 
     while (max_scan--) {
         void *entry = xas_prev(&xas);
         if (!entry || xa_is_value(entry))
             break;
         if (xas.xa_index == ULONG_MAX)
             break;
     }
 
     return xas.xa_index;
 }
 EXPORT_SYMBOL(page_cache_prev_miss);
 
 /*
  * Lockless page cache protocol:
  * On the lookup side:
  * 1. Load the folio from i_pages
  * 2. Increment the refcount if it's not zero
  * 3. If the folio is not found by xas_reload(), put the refcount and retry
  *
  * On the removal side:
  * A. Freeze the page (by zeroing the refcount if nobody else has a reference)
  * B. Remove the page from i_pages
  * C. Return the page to the page allocator
  *
  * This means that any page may have its reference count temporarily
  * increased by a speculative page cache (or fast GUP) lookup as it can
  * be allocated by another user before the RCU grace period expires.
  * Because the refcount temporarily acquired here may end up being the
  * last refcount on the page, any page allocation must be freeable by
  * folio_put().
  */
 
 /*
  * mapping_get_entry - Get a page cache entry.
  * @mapping: the address_space to search
  * @index: The page cache index.
  *
  * Looks up the page cache entry at @mapping & @index.  If it is a folio,
  * it is returned with an increased refcount.  If it is a shadow entry
  * of a previously evicted folio, or a swap entry from shmem/tmpfs,
  * it is returned without further action.
  *
  * Return: The folio, swap or shadow entry, %NULL if nothing is found.
  */
 static void *mapping_get_entry(struct address_space *mapping, pgoff_t index)
 {
     XA_STATE(xas, &mapping->i_pages, index);
     struct folio *folio;
 
     rcu_read_lock();
 repeat:
     xas_reset(&xas);
     folio = xas_load(&xas);
     if (xas_retry(&xas, folio))
         goto repeat;
     /*
      * A shadow entry of a recently evicted page, or a swap entry from
      * shmem/tmpfs.  Return it without attempting to raise page count.
      */
     if (!folio || xa_is_value(folio))
         goto out;
 
     if (!folio_try_get_rcu(folio))
         goto repeat;
 
     if (unlikely(folio != xas_reload(&xas))) {
         folio_put(folio);
         goto repeat;
     }
 out:
     rcu_read_unlock();
 
     return folio;
 }
 
 /**
  * __filemap_get_folio - Find and get a reference to a folio.
  * @mapping: The address_space to search.
  * @index: The page index.
  * @fgp_flags: %FGP flags modify how the folio is returned.
  * @gfp: Memory allocation flags to use if %FGP_CREAT is specified.
  *
  * Looks up the page cache entry at @mapping & @index.
  *
  * @fgp_flags can be zero or more of these flags:
  *
  * * %FGP_ACCESSED - The folio will be marked accessed.
  * * %FGP_LOCK - The folio is returned locked.
  * * %FGP_ENTRY - If there is a shadow / swap / DAX entry, return it
  *   instead of allocating a new folio to replace it.
  * * %FGP_CREAT - If no page is present then a new page is allocated using
  *   @gfp and added to the page cache and the VM's LRU list.
  *   The page is returned locked and with an increased refcount.
  * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
  *   page is already in cache.  If the page was allocated, unlock it before
  *   returning so the caller can do the same dance.
  * * %FGP_WRITE - The page will be written to by the caller.
  * * %FGP_NOFS - __GFP_FS will get cleared in gfp.
  * * %FGP_NOWAIT - Don't get blocked by page lock.
  * * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
  *
  * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
  * if the %GFP flags specified for %FGP_CREAT are atomic.
  *
  * If there is a page cache page, it is returned with an increased refcount.
  *
  * Return: The found folio or %NULL otherwise.
  */
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
         int fgp_flags, gfp_t gfp)
 {
     struct folio *folio;
 
 repeat:
     folio = mapping_get_entry(mapping, index);
     if (xa_is_value(folio)) {
         if (fgp_flags & FGP_ENTRY)
             return folio;
         folio = NULL;
     }
     if (!folio)
         goto no_page;
 
     if (fgp_flags & FGP_LOCK) {
         if (fgp_flags & FGP_NOWAIT) {
             if (!folio_trylock(folio)) {
                 folio_put(folio);
                 return NULL;
             }
         } else {
             folio_lock(folio);
         }
 
         /* Has the page been truncated? */
         if (unlikely(folio->mapping != mapping)) {
             folio_unlock(folio);
             folio_put(folio);
             goto repeat;
         }
         VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
     }
 
     if (fgp_flags & FGP_ACCESSED)
         folio_mark_accessed(folio);
     else if (fgp_flags & FGP_WRITE) {
         /* Clear idle flag for buffer write */
         if (folio_test_idle(folio))
             folio_clear_idle(folio);
     }
 
     if (fgp_flags & FGP_STABLE)
         folio_wait_stable(folio);
 no_page:
     if (!folio && (fgp_flags & FGP_CREAT)) {
         int err;
         if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
             gfp |= __GFP_WRITE;
         if (fgp_flags & FGP_NOFS)
             gfp &= ~__GFP_FS;
         if (fgp_flags & FGP_NOWAIT) {
             gfp &= ~GFP_KERNEL;
             gfp |= GFP_NOWAIT | __GFP_NOWARN;
         }
 
         folio = filemap_alloc_folio(gfp, 0);
         if (!folio)
             return NULL;
 
         if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
             fgp_flags |= FGP_LOCK;
 
         /* Init accessed so avoid atomic mark_page_accessed later */
         if (fgp_flags & FGP_ACCESSED)
             __folio_set_referenced(folio);
 
         err = filemap_add_folio(mapping, folio, index, gfp);
         if (unlikely(err)) {
             folio_put(folio);
             folio = NULL;
             if (err == -EEXIST)
                 goto repeat;
         }
 
         /*
          * filemap_add_folio locks the page, and for mmap
          * we expect an unlocked page.
          */
         if (folio && (fgp_flags & FGP_FOR_MMAP))
             folio_unlock(folio);
     }
 
     return folio;
 }
 EXPORT_SYMBOL(__filemap_get_folio);
 
 static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
         xa_mark_t mark)
 {
     struct folio *folio;
 
 retry:
     if (mark == XA_PRESENT)
         folio = xas_find(xas, max);
     else
         folio = xas_find_marked(xas, max, mark);
 
     if (xas_retry(xas, folio))
         goto retry;
     /*
      * A shadow entry of a recently evicted page, a swap
      * entry from shmem/tmpfs or a DAX entry.  Return it
      * without attempting to raise page count.
      */
     if (!folio || xa_is_value(folio))
         return folio;
 
     if (!folio_try_get_rcu(folio))
         goto reset;
 
     if (unlikely(folio != xas_reload(xas))) {
         folio_put(folio);
         goto reset;
     }
 
     return folio;
 reset:
     xas_reset(xas);
     goto retry;
 }
 
 /**
  * find_get_entries - gang pagecache lookup
  * @mapping:    The address_space to search
  * @start:  The starting page cache index
  * @end:    The final page index (inclusive).
  * @fbatch: Where the resulting entries are placed.
  * @indices:    The cache indices corresponding to the entries in @entries
  *
  * find_get_entries() will search for and return a batch of entries in
  * the mapping.  The entries are placed in @fbatch.  find_get_entries()
  * takes a reference on any actual folios it returns.
  *
  * The entries have ascending indexes.  The indices may not be consecutive
  * due to not-present entries or large folios.
  *
  * Any shadow entries of evicted folios, or swap entries from
  * shmem/tmpfs, are included in the returned array.
  *
  * Return: The number of entries which were found.
  */
 unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
         pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
 {
     XA_STATE(xas, &mapping->i_pages, start);
     struct folio *folio;
 
     rcu_read_lock();
     while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
         indices[fbatch->nr] = xas.xa_index;
         if (!folio_batch_add(fbatch, folio))
             break;
     }
     rcu_read_unlock();
 
     return folio_batch_count(fbatch);
 }
 
 /**
  * find_lock_entries - Find a batch of pagecache entries.
  * @mapping:    The address_space to search.
  * @start:  The starting page cache index.
  * @end:    The final page index (inclusive).
  * @fbatch: Where the resulting entries are placed.
  * @indices:    The cache indices of the entries in @fbatch.
  *
  * find_lock_entries() will return a batch of entries from @mapping.
  * Swap, shadow and DAX entries are included.  Folios are returned
  * locked and with an incremented refcount.  Folios which are locked
  * by somebody else or under writeback are skipped.  Folios which are
  * partially outside the range are not returned.
  *
  * The entries have ascending indexes.  The indices may not be consecutive
  * due to not-present entries, large folios, folios which could not be
  * locked or folios under writeback.
  *
  * Return: The number of entries which were found.
  */
 unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
         pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
 {
     XA_STATE(xas, &mapping->i_pages, start);
     struct folio *folio;
 
     rcu_read_lock();
     while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
         if (!xa_is_value(folio)) {
             if (folio->index < start)
                 goto put;
             if (folio->index + folio_nr_pages(folio) - 1 > end)
                 goto put;
             if (!folio_trylock(folio))
                 goto put;
             if (folio->mapping != mapping ||
                 folio_test_writeback(folio))
                 goto unlock;
             VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
                     folio);
         }
         indices[fbatch->nr] = xas.xa_index;
         if (!folio_batch_add(fbatch, folio))
             break;
         continue;
 unlock:
         folio_unlock(folio);
 put:
         folio_put(folio);
     }
     rcu_read_unlock();
 
     return folio_batch_count(fbatch);
 }
 
 /**
  * filemap_get_folios - Get a batch of folios
  * @mapping:    The address_space to search
  * @start:  The starting page index
  * @end:    The final page index (inclusive)
  * @fbatch: The batch to fill.
  *
  * Search for and return a batch of folios in the mapping starting at
  * index @start and up to index @end (inclusive).  The folios are returned
  * in @fbatch with an elevated reference count.
  *
  * The first folio may start before @start; if it does, it will contain
  * @start.  The final folio may extend beyond @end; if it does, it will
  * contain @end.  The folios have ascending indices.  There may be gaps
  * between the folios if there are indices which have no folio in the
  * page cache.  If folios are added to or removed from the page cache
  * while this is running, they may or may not be found by this call.
  *
  * Return: The number of folios which were found.
  * We also update @start to index the next folio for the traversal.
  */
 unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
         pgoff_t end, struct folio_batch *fbatch)
 {
     XA_STATE(xas, &mapping->i_pages, *start);
     struct folio *folio;
 
     rcu_read_lock();
     while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
         /* Skip over shadow, swap and DAX entries */
         if (xa_is_value(folio))
             continue;
         if (!folio_batch_add(fbatch, folio)) {
             unsigned long nr = folio_nr_pages(folio);
 
             if (folio_test_hugetlb(folio))
                 nr = 1;
             *start = folio->index + nr;
             goto out;
         }
     }
 
     /*
      * We come here when there is no page beyond @end. We take care to not
      * overflow the index @start as it confuses some of the callers. This
      * breaks the iteration when there is a page at index -1 but that is
      * already broken anyway.
      */
     if (end == (pgoff_t)-1)
         *start = (pgoff_t)-1;
     else
         *start = end + 1;
 out:
     rcu_read_unlock();
 
     return folio_batch_count(fbatch);
 }
 EXPORT_SYMBOL(filemap_get_folios);
 
 static inline
 bool folio_more_pages(struct folio *folio, pgoff_t index, pgoff_t max)
 {
     if (!folio_test_large(folio) || folio_test_hugetlb(folio))
         return false;
     if (index >= max)
         return false;
     return index < folio->index + folio_nr_pages(folio) - 1;
 }
 
 /**
  * find_get_pages_contig - gang contiguous pagecache lookup
  * @mapping:    The address_space to search
  * @index:  The starting page index
  * @nr_pages:   The maximum number of pages
  * @pages:  Where the resulting pages are placed
  *
  * find_get_pages_contig() works exactly like find_get_pages_range(),
  * except that the returned number of pages are guaranteed to be
  * contiguous.
  *
  * Return: the number of pages which were found.
  */
 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                    unsigned int nr_pages, struct page **pages)
 {
     XA_STATE(xas, &mapping->i_pages, index);
     struct folio *folio;
     unsigned int ret = 0;
 
     if (unlikely(!nr_pages))
         return 0;
 
     rcu_read_lock();
     for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
         if (xas_retry(&xas, folio))
             continue;
         /*
          * If the entry has been swapped out, we can stop looking.
          * No current caller is looking for DAX entries.
          */
         if (xa_is_value(folio))
             break;
 
         if (!folio_try_get_rcu(folio))
             goto retry;
 
         if (unlikely(folio != xas_reload(&xas)))
             goto put_page;
 
 again:
         pages[ret] = folio_file_page(folio, xas.xa_index);
         if (++ret == nr_pages)
             break;
         if (folio_more_pages(folio, xas.xa_index, ULONG_MAX)) {
             xas.xa_index++;
             folio_ref_inc(folio);
             goto again;
         }
         continue;
 put_page:
         folio_put(folio);
 retry:
         xas_reset(&xas);
     }
     rcu_read_unlock();
     return ret;
 }
 EXPORT_SYMBOL(find_get_pages_contig);
 
 /**
  * find_get_pages_range_tag - Find and return head pages matching @tag.
  * @mapping:    the address_space to search
  * @index:  the starting page index
  * @end:    The final page index (inclusive)
  * @tag:    the tag index
  * @nr_pages:   the maximum number of pages
  * @pages:  where the resulting pages are placed
  *
  * Like find_get_pages_range(), except we only return head pages which are
  * tagged with @tag.  @index is updated to the index immediately after the
  * last page we return, ready for the next iteration.
  *
  * Return: the number of pages which were found.
  */
 unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
             pgoff_t end, xa_mark_t tag, unsigned int nr_pages,
             struct page **pages)
 {
     XA_STATE(xas, &mapping->i_pages, *index);
     struct folio *folio;
     unsigned ret = 0;
 
     if (unlikely(!nr_pages))
         return 0;
 
     rcu_read_lock();
     while ((folio = find_get_entry(&xas, end, tag))) {
         /*
          * Shadow entries should never be tagged, but this iteration
          * is lockless so there is a window for page reclaim to evict
          * a page we saw tagged.  Skip over it.
          */
         if (xa_is_value(folio))
             continue;
 
         pages[ret] = &folio->page;
         if (++ret == nr_pages) {
             *index = folio->index + folio_nr_pages(folio);
             goto out;
         }
     }
 
     /*
      * We come here when we got to @end. We take care to not overflow the
      * index @index as it confuses some of the callers. This breaks the
      * iteration when there is a page at index -1 but that is already
      * broken anyway.
      */
     if (end == (pgoff_t)-1)
         *index = (pgoff_t)-1;
     else
         *index = end + 1;
 out:
     rcu_read_unlock();
 
     return ret;
 }
 EXPORT_SYMBOL(find_get_pages_range_tag);
 
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
  *
  *      ---R__________________________________________B__________
  *         ^ reading here                             ^ bad block(assume 4k)
  *
  * read(R) => miss => readahead(R...B) => media error => frustrating retries
  * => failing the whole request => read(R) => read(R+1) =>
  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
  *
  * It is going insane. Fix it by quickly scaling down the readahead size.
  */
 static void shrink_readahead_size_eio(struct file_ra_state *ra)
 {
     ra->ra_pages /= 4;
 }
 
 /*
  * filemap_get_read_batch - Get a batch of folios for read
  *
  * Get a batch of folios which represent a contiguous range of bytes in
  * the file.  No exceptional entries will be returned.  If @index is in
  * the middle of a folio, the entire folio will be returned.  The last
  * folio in the batch may have the readahead flag set or the uptodate flag
  * clear so that the caller can take the appropriate action.
  */
 static void filemap_get_read_batch(struct address_space *mapping,
         pgoff_t index, pgoff_t max, struct folio_batch *fbatch)
 {
     XA_STATE(xas, &mapping->i_pages, index);
     struct folio *folio;
 
     rcu_read_lock();
     for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
         if (xas_retry(&xas, folio))
             continue;
         if (xas.xa_index > max || xa_is_value(folio))
             break;
         if (xa_is_sibling(folio))
             break;
         if (!folio_try_get_rcu(folio))
             goto retry;
 
         if (unlikely(folio != xas_reload(&xas)))
             goto put_folio;
 
         if (!folio_batch_add(fbatch, folio))
             break;
         if (!folio_test_uptodate(folio))
             break;
         if (folio_test_readahead(folio))
             break;
         xas_advance(&xas, folio->index + folio_nr_pages(folio) - 1);
         continue;
 put_folio:
         folio_put(folio);
 retry:
         xas_reset(&xas);
     }
     rcu_read_unlock();
 }
 
 static int filemap_read_folio(struct file *file, filler_t filler,
         struct folio *folio)
 {
     int error;
 
     /*
      * A previous I/O error may have been due to temporary failures,
      * eg. multipath errors.  PG_error will be set again if read_folio
      * fails.
      */
     folio_clear_error(folio);
     /* Start the actual read. The read will unlock the page. */
     error = filler(file, folio);
     if (error)
         return error;
 
     error = folio_wait_locked_killable(folio);
     if (error)
         return error;
     if (folio_test_uptodate(folio))
         return 0;
     if (file)
         shrink_readahead_size_eio(&file->f_ra);
     return -EIO;
 }
 
 static bool filemap_range_uptodate(struct address_space *mapping,
         loff_t pos, struct iov_iter *iter, struct folio *folio)
 {
     int count;
 
     if (folio_test_uptodate(folio))
         return true;
     /* pipes can't handle partially uptodate pages */
     if (iov_iter_is_pipe(iter))
         return false;
     if (!mapping->a_ops->is_partially_uptodate)
         return false;
     if (mapping->host->i_blkbits >= folio_shift(folio))
         return false;
 
     count = iter->count;
     if (folio_pos(folio) > pos) {
         count -= folio_pos(folio) - pos;
         pos = 0;
     } else {
         pos -= folio_pos(folio);
     }
 
     return mapping->a_ops->is_partially_uptodate(folio, pos, count);
 }
 
 static int filemap_update_page(struct kiocb *iocb,
         struct address_space *mapping, struct iov_iter *iter,
         struct folio *folio)
 {
     int error;
 
     if (iocb->ki_flags & IOCB_NOWAIT) {
         if (!filemap_invalidate_trylock_shared(mapping))
             return -EAGAIN;
     } else {
         filemap_invalidate_lock_shared(mapping);
     }
 
     if (!folio_trylock(folio)) {
         error = -EAGAIN;
         if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
             goto unlock_mapping;
         if (!(iocb->ki_flags & IOCB_WAITQ)) {
             filemap_invalidate_unlock_shared(mapping);
             /*
              * This is where we usually end up waiting for a
              * previously submitted readahead to finish.
              */
             folio_put_wait_locked(folio, TASK_KILLABLE);
             return AOP_TRUNCATED_PAGE;
         }
         error = __folio_lock_async(folio, iocb->ki_waitq);
         if (error)
             goto unlock_mapping;
     }
 
     error = AOP_TRUNCATED_PAGE;
     if (!folio->mapping)
         goto unlock;
 
     error = 0;
     if (filemap_range_uptodate(mapping, iocb->ki_pos, iter, folio))
         goto unlock;
 
     error = -EAGAIN;
     if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
         goto unlock;
 
     error = filemap_read_folio(iocb->ki_filp, mapping->a_ops->read_folio,
             folio);
     goto unlock_mapping;
 unlock:
     folio_unlock(folio);
 unlock_mapping:
     filemap_invalidate_unlock_shared(mapping);
     if (error == AOP_TRUNCATED_PAGE)
         folio_put(folio);
     return error;
 }
 
 static int filemap_create_folio(struct file *file,
         struct address_space *mapping, pgoff_t index,
         struct folio_batch *fbatch)
 {
     struct folio *folio;
     int error;
 
     folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
     if (!folio)
         return -ENOMEM;
 
     /*
      * Protect against truncate / hole punch. Grabbing invalidate_lock
      * here assures we cannot instantiate and bring uptodate new
      * pagecache folios after evicting page cache during truncate
      * and before actually freeing blocks.  Note that we could
      * release invalidate_lock after inserting the folio into
      * the page cache as the locked folio would then be enough to
      * synchronize with hole punching. But there are code paths
      * such as filemap_update_page() filling in partially uptodate
      * pages or ->readahead() that need to hold invalidate_lock
      * while mapping blocks for IO so let's hold the lock here as
      * well to keep locking rules simple.
      */
     filemap_invalidate_lock_shared(mapping);
     error = filemap_add_folio(mapping, folio, index,
             mapping_gfp_constraint(mapping, GFP_KERNEL));
     if (error == -EEXIST)
         error = AOP_TRUNCATED_PAGE;
     if (error)
         goto error;
 
     error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
     if (error)
         goto error;
 
     filemap_invalidate_unlock_shared(mapping);
     folio_batch_add(fbatch, folio);
     return 0;
 error:
     filemap_invalidate_unlock_shared(mapping);
     folio_put(folio);
     return error;
 }
 
 static int filemap_readahead(struct kiocb *iocb, struct file *file,
         struct address_space *mapping, struct folio *folio,
         pgoff_t last_index)
 {
     DEFINE_READAHEAD(ractl, file, &file->f_ra, mapping, folio->index);
 
     if (iocb->ki_flags & IOCB_NOIO)
         return -EAGAIN;
     page_cache_async_ra(&ractl, folio, last_index - folio->index);
     return 0;
 }
 
 static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
         struct folio_batch *fbatch)
 {
     struct file *filp = iocb->ki_filp;
     struct address_space *mapping = filp->f_mapping;
     struct file_ra_state *ra = &filp->f_ra;
     pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
     pgoff_t last_index;
     struct folio *folio;
     int err = 0;
 
     last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE);
 retry:
     if (fatal_signal_pending(current))
         return -EINTR;
 
     filemap_get_read_batch(mapping, index, last_index, fbatch);
     if (!folio_batch_count(fbatch)) {
         if (iocb->ki_flags & IOCB_NOIO)
             return -EAGAIN;
         page_cache_sync_readahead(mapping, ra, filp, index,
                 last_index - index);
         filemap_get_read_batch(mapping, index, last_index, fbatch);
     }
     if (!folio_batch_count(fbatch)) {
         if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
             return -EAGAIN;
         err = filemap_create_folio(filp, mapping,
                 iocb->ki_pos >> PAGE_SHIFT, fbatch);
         if (err == AOP_TRUNCATED_PAGE)
             goto retry;
         return err;
     }
 
     folio = fbatch->folios[folio_batch_count(fbatch) - 1];
     if (folio_test_readahead(folio)) {
         err = filemap_readahead(iocb, filp, mapping, folio, last_index);
         if (err)
             goto err;
     }
     if (!folio_test_uptodate(folio)) {
         if ((iocb->ki_flags & IOCB_WAITQ) &&
             folio_batch_count(fbatch) > 1)
             iocb->ki_flags |= IOCB_NOWAIT;
         err = filemap_update_page(iocb, mapping, iter, folio);
         if (err)
             goto err;
     }
 
     return 0;
 err:
     if (err < 0)
         folio_put(folio);
     if (likely(--fbatch->nr))
         return 0;
     if (err == AOP_TRUNCATED_PAGE)
         goto retry;
     return err;
 }
 
 static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
 {
     unsigned int shift = folio_shift(folio);
 
     return (pos1 >> shift == pos2 >> shift);
 }
 
 /**
  * filemap_read - Read data from the page cache.
  * @iocb: The iocb to read.
  * @iter: Destination for the data.
  * @already_read: Number of bytes already read by the caller.
  *
  * Copies data from the page cache.  If the data is not currently present,
  * uses the readahead and read_folio address_space operations to fetch it.
  *
  * Return: Total number of bytes copied, including those already read by
  * the caller.  If an error happens before any bytes are copied, returns
  * a negative error number.
  */
 ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
         ssize_t already_read)
 {
     struct file *filp = iocb->ki_filp;
     struct file_ra_state *ra = &filp->f_ra;
     struct address_space *mapping = filp->f_mapping;
     struct inode *inode = mapping->host;
     struct folio_batch fbatch;
     int i, error = 0;
     bool writably_mapped;
     loff_t isize, end_offset;
 
     if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
         return 0;
     if (unlikely(!iov_iter_count(iter)))
         return 0;
 
     iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
     folio_batch_init(&fbatch);
 
     do {
         cond_resched();
 
         /*
          * If we've already successfully copied some data, then we
          * can no longer safely return -EIOCBQUEUED. Hence mark
          * an async read NOWAIT at that point.
          */
         if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
             iocb->ki_flags |= IOCB_NOWAIT;
 
         if (unlikely(iocb->ki_pos >= i_size_read(inode)))
             break;
 
         error = filemap_get_pages(iocb, iter, &fbatch);
         if (error < 0)
             break;
 
         /*
          * i_size must be checked after we know the pages are Uptodate.
          *
          * Checking i_size after the check allows us to calculate
          * the correct value for "nr", which means the zero-filled
          * part of the page is not copied back to userspace (unless
          * another truncate extends the file - this is desired though).
          */
         isize = i_size_read(inode);
         if (unlikely(iocb->ki_pos >= isize))
             goto put_folios;
         end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
 
         /*
          * Once we start copying data, we don't want to be touching any
          * cachelines that might be contended:
          */
         writably_mapped = mapping_writably_mapped(mapping);
 
         /*
          * When a read accesses the same folio several times, only
          * mark it as accessed the first time.
          */
         if (!pos_same_folio(iocb->ki_pos, ra->prev_pos - 1,
                             fbatch.folios[0]))
             folio_mark_accessed(fbatch.folios[0]);
 
         for (i = 0; i < folio_batch_count(&fbatch); i++) {
             struct folio *folio = fbatch.folios[i];
             size_t fsize = folio_size(folio);
             size_t offset = iocb->ki_pos & (fsize - 1);
             size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
                          fsize - offset);
             size_t copied;
 
             if (end_offset < folio_pos(folio))
                 break;
             if (i > 0)
                 folio_mark_accessed(folio);
             /*
              * If users can be writing to this folio using arbitrary
              * virtual addresses, take care of potential aliasing
              * before reading the folio on the kernel side.
              */
             if (writably_mapped)
                 flush_dcache_folio(folio);
 
             copied = copy_folio_to_iter(folio, offset, bytes, iter);
 
             already_read += copied;
             iocb->ki_pos += copied;
             ra->prev_pos = iocb->ki_pos;
 
             if (copied < bytes) {
                 error = -EFAULT;
                 break;
             }
         }
 put_folios:
         for (i = 0; i < folio_batch_count(&fbatch); i++)
             folio_put(fbatch.folios[i]);
         folio_batch_init(&fbatch);
     } while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
 
     file_accessed(filp);
 
     return already_read ? already_read : error;
 }
 EXPORT_SYMBOL_GPL(filemap_read);
 
 /**
  * generic_file_read_iter - generic filesystem read routine
  * @iocb:   kernel I/O control block
  * @iter:   destination for the data read
  *
  * This is the "read_iter()" routine for all filesystems
  * that can use the page cache directly.
  *
  * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
  * be returned when no data can be read without waiting for I/O requests
  * to complete; it doesn't prevent readahead.
  *
  * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
  * requests shall be made for the read or for readahead.  When no data
  * can be read, -EAGAIN shall be returned.  When readahead would be
  * triggered, a partial, possibly empty read shall be returned.
  *
  * Return:
  * * number of bytes copied, even for partial reads
  * * negative error code (or 0 if IOCB_NOIO) if nothing was read
  */
 ssize_t
 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
     size_t count = iov_iter_count(iter);
     ssize_t retval = 0;
 
     if (!count)
         return 0; /* skip atime */
 
     if (iocb->ki_flags & IOCB_DIRECT) {
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
         struct inode *inode = mapping->host;
 
         if (iocb->ki_flags & IOCB_NOWAIT) {
             if (filemap_range_needs_writeback(mapping, iocb->ki_pos,
                         iocb->ki_pos + count - 1))
                 return -EAGAIN;
         } else {
             retval = filemap_write_and_wait_range(mapping,
                         iocb->ki_pos,
                             iocb->ki_pos + count - 1);
             if (retval < 0)
                 return retval;
         }
 
         file_accessed(file);
 
         retval = mapping->a_ops->direct_IO(iocb, iter);
         if (retval >= 0) {
             iocb->ki_pos += retval;
             count -= retval;
         }
         if (retval != -EIOCBQUEUED)
             iov_iter_revert(iter, count - iov_iter_count(iter));
 
         /*
          * Btrfs can have a short DIO read if we encounter
          * compressed extents, so if there was an error, or if
          * we've already read everything we wanted to, or if
          * there was a short read because we hit EOF, go ahead
          * and return.  Otherwise fallthrough to buffered io for
          * the rest of the read.  Buffered reads will not work for
          * DAX files, so don't bother trying.
          */
         if (retval < 0 || !count || IS_DAX(inode))
             return retval;
         if (iocb->ki_pos >= i_size_read(inode))
             return retval;
     }
 
     return filemap_read(iocb, iter, retval);
 }
 EXPORT_SYMBOL(generic_file_read_iter);
 
 static inline loff_t folio_seek_hole_data(struct xa_state *xas,
         struct address_space *mapping, struct folio *folio,
         loff_t start, loff_t end, bool seek_data)
 {
     const struct address_space_operations *ops = mapping->a_ops;
     size_t offset, bsz = i_blocksize(mapping->host);
 
     if (xa_is_value(folio) || folio_test_uptodate(folio))
         return seek_data ? start : end;
     if (!ops->is_partially_uptodate)
         return seek_data ? end : start;
 
     xas_pause(xas);
     rcu_read_unlock();
     folio_lock(folio);
     if (unlikely(folio->mapping != mapping))
         goto unlock;
 
     offset = offset_in_folio(folio, start) & ~(bsz - 1);
 
     do {
         if (ops->is_partially_uptodate(folio, offset, bsz) ==
                             seek_data)
             break;
         start = (start + bsz) & ~(bsz - 1);
         offset += bsz;
     } while (offset < folio_size(folio));
 unlock:
     folio_unlock(folio);
     rcu_read_lock();
     return start;
 }
 
 static inline size_t seek_folio_size(struct xa_state *xas, struct folio *folio)
 {
     if (xa_is_value(folio))
         return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
     return folio_size(folio);
 }
 
 /**
  * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
  * @mapping: Address space to search.
  * @start: First byte to consider.
  * @end: Limit of search (exclusive).
  * @whence: Either SEEK_HOLE or SEEK_DATA.
  *
  * If the page cache knows which blocks contain holes and which blocks
  * contain data, your filesystem can use this function to implement
  * SEEK_HOLE and SEEK_DATA.  This is useful for filesystems which are
  * entirely memory-based such as tmpfs, and filesystems which support
  * unwritten extents.
  *
  * Return: The requested offset on success, or -ENXIO if @whence specifies
  * SEEK_DATA and there is no data after @start.  There is an implicit hole
  * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
  * and @end contain data.
  */
 loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
         loff_t end, int whence)
 {
     XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
     pgoff_t max = (end - 1) >> PAGE_SHIFT;
     bool seek_data = (whence == SEEK_DATA);
     struct folio *folio;
 
     if (end <= start)
         return -ENXIO;
 
     rcu_read_lock();
     while ((folio = find_get_entry(&xas, max, XA_PRESENT))) {
         loff_t pos = (u64)xas.xa_index << PAGE_SHIFT;
         size_t seek_size;
 
         if (start < pos) {
             if (!seek_data)
                 goto unlock;
             start = pos;
         }
 
         seek_size = seek_folio_size(&xas, folio);
         pos = round_up((u64)pos + 1, seek_size);
         start = folio_seek_hole_data(&xas, mapping, folio, start, pos,
                 seek_data);
         if (start < pos)
             goto unlock;
         if (start >= end)
             break;
         if (seek_size > PAGE_SIZE)
             xas_set(&xas, pos >> PAGE_SHIFT);
         if (!xa_is_value(folio))
             folio_put(folio);
     }
     if (seek_data)
         start = -ENXIO;
 unlock:
     rcu_read_unlock();
     if (folio && !xa_is_value(folio))
         folio_put(folio);
     if (start > end)
         return end;
     return start;
 }
 
 #ifdef CONFIG_MMU
 #define MMAP_LOTSAMISS  (100)
 /*
  * lock_folio_maybe_drop_mmap - lock the page, possibly dropping the mmap_lock
  * @vmf - the vm_fault for this fault.
  * @folio - the folio to lock.
  * @fpin - the pointer to the file we may pin (or is already pinned).
  *
  * This works similar to lock_folio_or_retry in that it can drop the
  * mmap_lock.  It differs in that it actually returns the folio locked
  * if it returns 1 and 0 if it couldn't lock the folio.  If we did have
  * to drop the mmap_lock then fpin will point to the pinned file and
  * needs to be fput()'ed at a later point.
  */
 static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio,
                      struct file **fpin)
 {
     if (folio_trylock(folio))
         return 1;
 
     /*
      * NOTE! This will make us return with VM_FAULT_RETRY, but with
      * the mmap_lock still held. That's how FAULT_FLAG_RETRY_NOWAIT
      * is supposed to work. We have way too many special cases..
      */
     if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
         return 0;
 
     *fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
     if (vmf->flags & FAULT_FLAG_KILLABLE) {
         if (__folio_lock_killable(folio)) {
             /*
              * We didn't have the right flags to drop the mmap_lock,
              * but all fault_handlers only check for fatal signals
              * if we return VM_FAULT_RETRY, so we need to drop the
              * mmap_lock here and return 0 if we don't have a fpin.
              */
             if (*fpin == NULL)
                 mmap_read_unlock(vmf->vma->vm_mm);
             return 0;
         }
     } else
         __folio_lock(folio);
 
     return 1;
 }
 
 /*
  * Synchronous readahead happens when we don't even find a page in the page
  * cache at all.  We don't want to perform IO under the mmap sem, so if we have
  * to drop the mmap sem we return the file that was pinned in order for us to do
  * that.  If we didn't pin a file then we return NULL.  The file that is
  * returned needs to be fput()'ed when we're done with it.
  */
 static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 {
     struct file *file = vmf->vma->vm_file;
     struct file_ra_state *ra = &file->f_ra;
     struct address_space *mapping = file->f_mapping;
     DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
     struct file *fpin = NULL;
     unsigned long vm_flags = vmf->vma->vm_flags;
     unsigned int mmap_miss;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
     /* Use the readahead code, even if readahead is disabled */
     if (vm_flags & VM_HUGEPAGE) {
         fpin = maybe_unlock_mmap_for_io(vmf, fpin);
         ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
         ra->size = HPAGE_PMD_NR;
         /*
          * Fetch two PMD folios, so we get the chance to actually
          * readahead, unless we've been told not to.
          */
         if (!(vm_flags & VM_RAND_READ))
             ra->size *= 2;
         ra->async_size = HPAGE_PMD_NR;
         page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
         return fpin;
     }
 #endif
 
     /* If we don't want any read-ahead, don't bother */
     if (vm_flags & VM_RAND_READ)
         return fpin;
     if (!ra->ra_pages)
         return fpin;
 
     if (vm_flags & VM_SEQ_READ) {
         fpin = maybe_unlock_mmap_for_io(vmf, fpin);
         page_cache_sync_ra(&ractl, ra->ra_pages);
         return fpin;
     }
 
     /* Avoid banging the cache line if not needed */
     mmap_miss = READ_ONCE(ra->mmap_miss);
     if (mmap_miss < MMAP_LOTSAMISS * 10)
         WRITE_ONCE(ra->mmap_miss, ++mmap_miss);
 
     /*
      * Do we miss much more than hit in this file? If so,
      * stop bothering with read-ahead. It will only hurt.
      */
     if (mmap_miss > MMAP_LOTSAMISS)
         return fpin;
 
     /*
      * mmap read-around
      */
     fpin = maybe_unlock_mmap_for_io(vmf, fpin);
     ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
     ra->size = ra->ra_pages;
     ra->async_size = ra->ra_pages / 4;
     ractl._index = ra->start;
     page_cache_ra_order(&ractl, ra, 0);
     return fpin;
 }
 
 /*
  * Asynchronous readahead happens when we find the page and PG_readahead,
  * so we want to possibly extend the readahead further.  We return the file that
  * was pinned if we have to drop the mmap_lock in order to do IO.
  */
 static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
                         struct folio *folio)
 {
     struct file *file = vmf->vma->vm_file;
     struct file_ra_state *ra = &file->f_ra;
     DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
     struct file *fpin = NULL;
     unsigned int mmap_miss;
 
     /* If we don't want any read-ahead, don't bother */
     if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
         return fpin;
 
     mmap_miss = READ_ONCE(ra->mmap_miss);
     if (mmap_miss)
         WRITE_ONCE(ra->mmap_miss, --mmap_miss);
 
     if (folio_test_readahead(folio)) {
         fpin = maybe_unlock_mmap_for_io(vmf, fpin);
         page_cache_async_ra(&ractl, folio, ra->ra_pages);
     }
     return fpin;
 }
 
 /**
  * filemap_fault - read in file data for page fault handling
  * @vmf:    struct vm_fault containing details of the fault
  *
  * filemap_fault() is invoked via the vma operations vector for a
  * mapped memory region to read in file data during a page fault.
  *
  * The goto's are kind of ugly, but this streamlines the normal case of having
  * it in the page cache, and handles the special cases reasonably without
  * having a lot of duplicated code.
  *
  * vma->vm_mm->mmap_lock must be held on entry.
  *
  * If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
  * may be dropped before doing I/O or by lock_folio_maybe_drop_mmap().
  *
  * If our return value does not have VM_FAULT_RETRY set, the mmap_lock
  * has not been released.
  *
  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
  *
  * Return: bitwise-OR of %VM_FAULT_ codes.
  */
 vm_fault_t filemap_fault(struct vm_fault *vmf)
 {
     int error;
     struct file *file = vmf->vma->vm_file;
     struct file *fpin = NULL;
     struct address_space *mapping = file->f_mapping;
     struct inode *inode = mapping->host;
     pgoff_t max_idx, index = vmf->pgoff;
     struct folio *folio;
     vm_fault_t ret = 0;
     bool mapping_locked = false;
 
     max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
     if (unlikely(index >= max_idx))
         return VM_FAULT_SIGBUS;
 
     /*
      * Do we have something in the page cache already?
      */
     folio = filemap_get_folio(mapping, index);
     if (likely(folio)) {
         /*
          * We found the page, so try async readahead before waiting for
          * the lock.
          */
         if (!(vmf->flags & FAULT_FLAG_TRIED))
             fpin = do_async_mmap_readahead(vmf, folio);
         if (unlikely(!folio_test_uptodate(folio))) {
             filemap_invalidate_lock_shared(mapping);
             mapping_locked = true;
         }
     } else {
         /* No page in the page cache at all */
         count_vm_event(PGMAJFAULT);
         count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
         ret = VM_FAULT_MAJOR;
         fpin = do_sync_mmap_readahead(vmf);
 retry_find:
         /*
          * See comment in filemap_create_folio() why we need
          * invalidate_lock
          */
         if (!mapping_locked) {
             filemap_invalidate_lock_shared(mapping);
             mapping_locked = true;
         }
         folio = __filemap_get_folio(mapping, index,
                       FGP_CREAT|FGP_FOR_MMAP,
                       vmf->gfp_mask);
         if (!folio) {
             if (fpin)
                 goto out_retry;
             filemap_invalidate_unlock_shared(mapping);
             return VM_FAULT_OOM;
         }
     }
 
     if (!lock_folio_maybe_drop_mmap(vmf, folio, &fpin))
         goto out_retry;
 
     /* Did it get truncated? */
     if (unlikely(folio->mapping != mapping)) {
         folio_unlock(folio);
         folio_put(folio);
         goto retry_find;
     }
     VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
 
     /*
      * We have a locked page in the page cache, now we need to check
      * that it's up-to-date. If not, it is going to be due to an error.
      */
     if (unlikely(!folio_test_uptodate(folio))) {
         /*
          * The page was in cache and uptodate and now it is not.
          * Strange but possible since we didn't hold the page lock all
          * the time. Let's drop everything get the invalidate lock and
          * try again.
          */
         if (!mapping_locked) {
             folio_unlock(folio);
             folio_put(folio);
             goto retry_find;
         }
         goto page_not_uptodate;
     }
 
     /*
      * We've made it this far and we had to drop our mmap_lock, now is the
      * time to return to the upper layer and have it re-find the vma and
      * redo the fault.
      */
     if (fpin) {
         folio_unlock(folio);
         goto out_retry;
     }
     if (mapping_locked)
         filemap_invalidate_unlock_shared(mapping);
 
     /*
      * Found the page and have a reference on it.
      * We must recheck i_size under page lock.
      */
     max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
     if (unlikely(index >= max_idx)) {
         folio_unlock(folio);
         folio_put(folio);
         return VM_FAULT_SIGBUS;
     }
 
     vmf->page = folio_file_page(folio, index);
     return ret | VM_FAULT_LOCKED;
 
 page_not_uptodate:
     /*
      * Umm, take care of errors if the page isn't up-to-date.
      * Try to re-read it _once_. We do this synchronously,
      * because there really aren't any performance issues here
      * and we need to check for errors.
      */
     fpin = maybe_unlock_mmap_for_io(vmf, fpin);
     error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
     if (fpin)
         goto out_retry;
     folio_put(folio);
 
     if (!error || error == AOP_TRUNCATED_PAGE)
         goto retry_find;
     filemap_invalidate_unlock_shared(mapping);
 
     return VM_FAULT_SIGBUS;
 
 out_retry:
     /*
      * We dropped the mmap_lock, we need to return to the fault handler to
      * re-find the vma and come back and find our hopefully still populated
      * page.
      */
     if (folio)
         folio_put(folio);
     if (mapping_locked)
         filemap_invalidate_unlock_shared(mapping);
     if (fpin)
         fput(fpin);
     return ret | VM_FAULT_RETRY;
 }
 EXPORT_SYMBOL(filemap_fault);
 
 static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 {
     struct mm_struct *mm = vmf->vma->vm_mm;
 
     /* Huge page is mapped? No need to proceed. */
     if (pmd_trans_huge(*vmf->pmd)) {
         unlock_page(page);
         put_page(page);
         return true;
     }
 
     if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
         vm_fault_t ret = do_set_pmd(vmf, page);
         if (!ret) {
             /* The page is mapped successfully, reference consumed. */
             unlock_page(page);
             return true;
         }
     }
 
     if (pmd_none(*vmf->pmd))
         pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
 
     /* See comment in handle_pte_fault() */
     if (pmd_devmap_trans_unstable(vmf->pmd)) {
         unlock_page(page);
         put_page(page);
         return true;
     }
 
     return false;
 }
 
 static struct folio *next_uptodate_page(struct folio *folio,
                        struct address_space *mapping,
                        struct xa_state *xas, pgoff_t end_pgoff)
 {
     unsigned long max_idx;
 
     do {
         if (!folio)
             return NULL;
         if (xas_retry(xas, folio))
             continue;
         if (xa_is_value(folio))
             continue;
         if (folio_test_locked(folio))
             continue;
         if (!folio_try_get_rcu(folio))
             continue;
         /* Has the page moved or been split? */
         if (unlikely(folio != xas_reload(xas)))
             goto skip;
         if (!folio_test_uptodate(folio) || folio_test_readahead(folio))
             goto skip;
         if (!folio_trylock(folio))
             goto skip;
         if (folio->mapping != mapping)
             goto unlock;
         if (!folio_test_uptodate(folio))
             goto unlock;
         max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
         if (xas->xa_index >= max_idx)
             goto unlock;
         return folio;
 unlock:
         folio_unlock(folio);
 skip:
         folio_put(folio);
     } while ((folio = xas_next_entry(xas, end_pgoff)) != NULL);
 
     return NULL;
 }
 
 static inline struct folio *first_map_page(struct address_space *mapping,
                       struct xa_state *xas,
                       pgoff_t end_pgoff)
 {
     return next_uptodate_page(xas_find(xas, end_pgoff),
                   mapping, xas, end_pgoff);
 }
 
 static inline struct folio *next_map_page(struct address_space *mapping,
                      struct xa_state *xas,
                      pgoff_t end_pgoff)
 {
     return next_uptodate_page(xas_next_entry(xas, end_pgoff),
                   mapping, xas, end_pgoff);
 }
 
 vm_fault_t filemap_map_pages(struct vm_fault *vmf,
                  pgoff_t start_pgoff, pgoff_t end_pgoff)
 {
     struct vm_area_struct *vma = vmf->vma;
     struct file *file = vma->vm_file;
     struct address_space *mapping = file->f_mapping;
     pgoff_t last_pgoff = start_pgoff;
     unsigned long addr;
     XA_STATE(xas, &mapping->i_pages, start_pgoff);
     struct folio *folio;
     struct page *page;
     unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
     vm_fault_t ret = 0;
 
     rcu_read_lock();
     folio = first_map_page(mapping, &xas, end_pgoff);
     if (!folio)
         goto out;
 
     if (filemap_map_pmd(vmf, &folio->page)) {
         ret = VM_FAULT_NOPAGE;
         goto out;
     }
 
     addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
     vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
     do {
 again:
         page = folio_file_page(folio, xas.xa_index);
         if (PageHWPoison(page))
             goto unlock;
 
         if (mmap_miss > 0)
             mmap_miss--;
 
         addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
         vmf->pte += xas.xa_index - last_pgoff;
         last_pgoff = xas.xa_index;
 
         /*
          * NOTE: If there're PTE markers, we'll leave them to be
          * handled in the specific fault path, and it'll prohibit the
          * fault-around logic.
          */
         if (!pte_none(*vmf->pte))
             goto unlock;
 
         /* We're about to handle the fault */
         if (vmf->address == addr)
             ret = VM_FAULT_NOPAGE;
 
         do_set_pte(vmf, page, addr);
         /* no need to invalidate: a not-present page won't be cached */
         update_mmu_cache(vma, addr, vmf->pte);
         if (folio_more_pages(folio, xas.xa_index, end_pgoff)) {
             xas.xa_index++;
             folio_ref_inc(folio);
             goto again;
         }
         folio_unlock(folio);
         continue;
 unlock:
         if (folio_more_pages(folio, xas.xa_index, end_pgoff)) {
             xas.xa_index++;
             goto again;
         }
         folio_unlock(folio);
         folio_put(folio);
     } while ((folio = next_map_page(mapping, &xas, end_pgoff)) != NULL);
     pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
     rcu_read_unlock();
     WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss);
     return ret;
 }
 EXPORT_SYMBOL(filemap_map_pages);
 
 vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     struct folio *folio = page_folio(vmf->page);
     vm_fault_t ret = VM_FAULT_LOCKED;
 
     sb_start_pagefault(mapping->host->i_sb);
     file_update_time(vmf->vma->vm_file);
     folio_lock(folio);
     if (folio->mapping != mapping) {
         folio_unlock(folio);
         ret = VM_FAULT_NOPAGE;
         goto out;
     }
     /*
      * We mark the folio dirty already here so that when freeze is in
      * progress, we are guaranteed that writeback during freezing will
      * see the dirty folio and writeprotect it again.
      */
     folio_mark_dirty(folio);
     folio_wait_stable(folio);
 out:
     sb_end_pagefault(mapping->host->i_sb);
     return ret;
 }
 
 const struct vm_operations_struct generic_file_vm_ops = {
     .fault      = filemap_fault,
     .map_pages  = filemap_map_pages,
     .page_mkwrite   = filemap_page_mkwrite,
 };
 
 /* This is used for a general mmap of a disk file */
 
 int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
     struct address_space *mapping = file->f_mapping;
 
     if (!mapping->a_ops->read_folio)
         return -ENOEXEC;
     file_accessed(file);
     vma->vm_ops = &generic_file_vm_ops;
     return 0;
 }
 
 /*
  * This is for filesystems which do not implement ->writepage.
  */
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
     if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
         return -EINVAL;
     return generic_file_mmap(file, vma);
 }
 #else
 vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
     return VM_FAULT_SIGBUS;
 }
 int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
     return -ENOSYS;
 }
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
     return -ENOSYS;
 }
 #endif /* CONFIG_MMU */
 
 EXPORT_SYMBOL(filemap_page_mkwrite);
 EXPORT_SYMBOL(generic_file_mmap);
 EXPORT_SYMBOL(generic_file_readonly_mmap);
 
 static struct folio *do_read_cache_folio(struct address_space *mapping,
         pgoff_t index, filler_t filler, struct file *file, gfp_t gfp)
 {
     struct folio *folio;
     int err;
 
     if (!filler)
         filler = mapping->a_ops->read_folio;
 repeat:
     folio = filemap_get_folio(mapping, index);
     if (!folio) {
         folio = filemap_alloc_folio(gfp, 0);
         if (!folio)
             return ERR_PTR(-ENOMEM);
         err = filemap_add_folio(mapping, folio, index, gfp);
         if (unlikely(err)) {
             folio_put(folio);
             if (err == -EEXIST)
                 goto repeat;
             /* Presumably ENOMEM for xarray node */
             return ERR_PTR(err);
         }
 
         goto filler;
     }
     if (folio_test_uptodate(folio))
         goto out;
 
     if (!folio_trylock(folio)) {
         folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE);
         goto repeat;
     }
 
     /* Folio was truncated from mapping */
     if (!folio->mapping) {
         folio_unlock(folio);
         folio_put(folio);
         goto repeat;
     }
 
     /* Someone else locked and filled the page in a very small window */
     if (folio_test_uptodate(folio)) {
         folio_unlock(folio);
         goto out;
     }
 
 filler:
     err = filemap_read_folio(file, filler, folio);
     if (err) {
         folio_put(folio);
         if (err == AOP_TRUNCATED_PAGE)
             goto repeat;
         return ERR_PTR(err);
     }
 
 out:
     folio_mark_accessed(folio);
     return folio;
 }
 
 /**
  * read_cache_folio - Read into page cache, fill it if needed.
  * @mapping: The address_space to read from.
  * @index: The index to read.
  * @filler: Function to perform the read, or NULL to use aops->read_folio().
  * @file: Passed to filler function, may be NULL if not required.
  *
  * Read one page into the page cache.  If it succeeds, the folio returned
  * will contain @index, but it may not be the first page of the folio.
  *
  * If the filler function returns an error, it will be returned to the
  * caller.
  *
  * Context: May sleep.  Expects mapping->invalidate_lock to be held.
  * Return: An uptodate folio on success, ERR_PTR() on failure.
  */
 struct folio *read_cache_folio(struct address_space *mapping, pgoff_t index,
         filler_t filler, struct file *file)
 {
     return do_read_cache_folio(mapping, index, filler, file,
             mapping_gfp_mask(mapping));
 }
 EXPORT_SYMBOL(read_cache_folio);
 
 static struct page *do_read_cache_page(struct address_space *mapping,
         pgoff_t index, filler_t *filler, struct file *file, gfp_t gfp)
 {
     struct folio *folio;
 
     folio = do_read_cache_folio(mapping, index, filler, file, gfp);
     if (IS_ERR(folio))
         return &folio->page;
     return folio_file_page(folio, index);
 }
 
 struct page *read_cache_page(struct address_space *mapping,
             pgoff_t index, filler_t *filler, struct file *file)
 {
     return do_read_cache_page(mapping, index, filler, file,
             mapping_gfp_mask(mapping));
 }
 EXPORT_SYMBOL(read_cache_page);
 
 /**
  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
  * @mapping:    the page's address_space
  * @index:  the page index
  * @gfp:    the page allocator flags to use if allocating
  *
  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
  * any new page allocations done using the specified allocation flags.
  *
  * If the page does not get brought uptodate, return -EIO.
  *
  * The function expects mapping->invalidate_lock to be already held.
  *
  * Return: up to date page on success, ERR_PTR() on failure.
  */
 struct page *read_cache_page_gfp(struct address_space *mapping,
                 pgoff_t index,
                 gfp_t gfp)
 {
     return do_read_cache_page(mapping, index, NULL, NULL, gfp);
 }
 EXPORT_SYMBOL(read_cache_page_gfp);
 
 /*
  * Warn about a page cache invalidation failure during a direct I/O write.
  */
 void dio_warn_stale_pagecache(struct file *filp)
 {
     static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
     char pathname[128];
     char *path;
 
     errseq_set(&filp->f_mapping->wb_err, -EIO);
     if (__ratelimit(&_rs)) {
         path = file_path(filp, pathname, sizeof(pathname));
         if (IS_ERR(path))
             path = "(unknown)";
         pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
         pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
             current->comm);
     }
 }
 
 ssize_t
 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {
     struct file *file = iocb->ki_filp;
     struct address_space *mapping = file->f_mapping;
     struct inode    *inode = mapping->host;
     loff_t      pos = iocb->ki_pos;
     ssize_t     written;
     size_t      write_len;
     pgoff_t     end;
 
     write_len = iov_iter_count(from);
     end = (pos + write_len - 1) >> PAGE_SHIFT;
 
     if (iocb->ki_flags & IOCB_NOWAIT) {
         /* If there are pages to writeback, return */
         if (filemap_range_has_page(file->f_mapping, pos,
                        pos + write_len - 1))
             return -EAGAIN;
     } else {
         written = filemap_write_and_wait_range(mapping, pos,
                             pos + write_len - 1);
         if (written)
             goto out;
     }
 
     /*
      * After a write we want buffered reads to be sure to go to disk to get
      * the new data.  We invalidate clean cached page from the region we're
      * about to write.  We do this *before* the write so that we can return
      * without clobbering -EIOCBQUEUED from ->direct_IO().
      */
     written = invalidate_inode_pages2_range(mapping,
                     pos >> PAGE_SHIFT, end);
     /*
      * If a page can not be invalidated, return 0 to fall back
      * to buffered write.
      */
     if (written) {
         if (written == -EBUSY)
             return 0;
         goto out;
     }
 
     written = mapping->a_ops->direct_IO(iocb, from);
 
     /*
      * Finally, try again to invalidate clean pages which might have been
      * cached by non-direct readahead, or faulted in by get_user_pages()
      * if the source of the write was an mmap'ed region of the file
      * we're writing.  Either one is a pretty crazy thing to do,
      * so we don't support it 100%.  If this invalidation
      * fails, tough, the write still worked...
      *
      * Most of the time we do not need this since dio_complete() will do
      * the invalidation for us. However there are some file systems that
      * do not end up with dio_complete() being called, so let's not break
      * them by removing it completely.
      *
      * Noticeable example is a blkdev_direct_IO().
      *
      * Skip invalidation for async writes or if mapping has no pages.
      */
     if (written > 0 && mapping->nrpages &&
         invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT, end))
         dio_warn_stale_pagecache(file);
 
     if (written > 0) {
         pos += written;
         write_len -= written;
         if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
             i_size_write(inode, pos);
             mark_inode_dirty(inode);
         }
         iocb->ki_pos = pos;
     }
     if (written != -EIOCBQUEUED)
         iov_iter_revert(from, write_len - iov_iter_count(from));
 out:
     return written;
 }
 EXPORT_SYMBOL(generic_file_direct_write);
 
 ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
 {
     struct file *file = iocb->ki_filp;
     loff_t pos = iocb->ki_pos;
     struct address_space *mapping = file->f_mapping;
     const struct address_space_operations *a_ops = mapping->a_ops;
     long status = 0;
     ssize_t written = 0;
 
     do {
         struct page *page;
         unsigned long offset;   /* Offset into pagecache page */
         unsigned long bytes;    /* Bytes to write to page */
         size_t copied;      /* Bytes copied from user */
         void *fsdata;
 
         offset = (pos & (PAGE_SIZE - 1));
         bytes = min_t(unsigned long, PAGE_SIZE - offset,
                         iov_iter_count(i));
 
 again:
         /*
          * Bring in the user page that we will copy from _first_.
          * Otherwise there's a nasty deadlock on copying from the
          * same page as we're writing to, without it being marked
          * up-to-date.
          */
         if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
             status = -EFAULT;
             break;
         }
 
         if (fatal_signal_pending(current)) {
             status = -EINTR;
             break;
         }
 
         status = a_ops->write_begin(file, mapping, pos, bytes,
                         &page, &fsdata);
         if (unlikely(status < 0))
             break;
 
         if (mapping_writably_mapped(mapping))
             flush_dcache_page(page);
 
         copied = copy_page_from_iter_atomic(page, offset, bytes, i);
         flush_dcache_page(page);
 
         status = a_ops->write_end(file, mapping, pos, bytes, copied,
                         page, fsdata);
         if (unlikely(status != copied)) {
             iov_iter_revert(i, copied - max(status, 0L));
             if (unlikely(status < 0))
                 break;
         }
         cond_resched();
 
         if (unlikely(status == 0)) {
             /*
              * A short copy made ->write_end() reject the
              * thing entirely.  Might be memory poisoning
              * halfway through, might be a race with munmap,
              * might be severe memory pressure.
              */
             if (copied)
                 bytes = copied;
             goto again;
         }
         pos += status;
         written += status;
 
         balance_dirty_pages_ratelimited(mapping);
     } while (iov_iter_count(i));
 
     return written ? written : status;
 }
 EXPORT_SYMBOL(generic_perform_write);
 
 /**
  * __generic_file_write_iter - write data to a file
  * @iocb:   IO state structure (file, offset, etc.)
  * @from:   iov_iter with data to write
  *
  * This function does all the work needed for actually writing data to a
  * file. It does all basic checks, removes SUID from the file, updates
  * modification times and calls proper subroutines depending on whether we
  * do direct IO or a standard buffered write.
  *
  * It expects i_rwsem to be grabbed unless we work on a block device or similar
  * object which does not need locking at all.
  *
  * This function does *not* take care of syncing data in case of O_SYNC write.
  * A caller has to handle it. This is mainly due to the fact that we want to
  * avoid syncing under i_rwsem.
  *
  * Return:
  * * number of bytes written, even for truncated writes
  * * negative error code if no data has been written at all
  */
 ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
     struct file *file = iocb->ki_filp;
     struct address_space *mapping = file->f_mapping;
     struct inode    *inode = mapping->host;
     ssize_t     written = 0;
     ssize_t     err;
     ssize_t     status;
 
     /* We can write back this queue in page reclaim */
     current->backing_dev_info = inode_to_bdi(inode);
     err = file_remove_privs(file);
     if (err)
         goto out;
 
     err = file_update_time(file);
     if (err)
         goto out;
 
     if (iocb->ki_flags & IOCB_DIRECT) {
         loff_t pos, endbyte;
 
         written = generic_file_direct_write(iocb, from);
         /*
          * If the write stopped short of completing, fall back to
          * buffered writes.  Some filesystems do this for writes to
          * holes, for example.  For DAX files, a buffered write will
          * not succeed (even if it did, DAX does not handle dirty
          * page-cache pages correctly).
          */
         if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
             goto out;
 
         pos = iocb->ki_pos;
         status = generic_perform_write(iocb, from);
         /*
          * If generic_perform_write() returned a synchronous error
          * then we want to return the number of bytes which were
          * direct-written, or the error code if that was zero.  Note
          * that this differs from normal direct-io semantics, which
          * will return -EFOO even if some bytes were written.
          */
         if (unlikely(status < 0)) {
             err = status;
             goto out;
         }
         /*
          * We need to ensure that the page cache pages are written to
          * disk and invalidated to preserve the expected O_DIRECT
          * semantics.
          */
         endbyte = pos + status - 1;
         err = filemap_write_and_wait_range(mapping, pos, endbyte);
         if (err == 0) {
             iocb->ki_pos = endbyte + 1;
             written += status;
             invalidate_mapping_pages(mapping,
                          pos >> PAGE_SHIFT,
                          endbyte >> PAGE_SHIFT);
         } else {
             /*
              * We don't know how much we wrote, so just return
              * the number of bytes which were direct-written
              */
         }
     } else {
         written = generic_perform_write(iocb, from);
         if (likely(written > 0))
             iocb->ki_pos += written;
     }
 out:
     current->backing_dev_info = NULL;
     return written ? written : err;
 }
 EXPORT_SYMBOL(__generic_file_write_iter);
 
 /**
  * generic_file_write_iter - write data to a file
  * @iocb:   IO state structure
  * @from:   iov_iter with data to write
  *
  * This is a wrapper around __generic_file_write_iter() to be used by most
  * filesystems. It takes care of syncing the file in case of O_SYNC file
  * and acquires i_rwsem as needed.
  * Return:
  * * negative error code if no data has been written at all of
  *   vfs_fsync_range() failed for a synchronous write
  * * number of bytes written, even for truncated writes
  */
 ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
     struct file *file = iocb->ki_filp;
     struct inode *inode = file->f_mapping->host;
     ssize_t ret;
 
     inode_lock(inode);
     ret = generic_write_checks(iocb, from);
     if (ret > 0)
         ret = __generic_file_write_iter(iocb, from);
     inode_unlock(inode);
 
     if (ret > 0)
         ret = generic_write_sync(iocb, ret);
     return ret;
 }
 EXPORT_SYMBOL(generic_file_write_iter);
 
 /**
  * filemap_release_folio() - Release fs-specific metadata on a folio.
  * @folio: The folio which the kernel is trying to free.
  * @gfp: Memory allocation flags (and I/O mode).
  *
  * The address_space is trying to release any data attached to a folio
  * (presumably at folio->private).
  *
  * This will also be called if the private_2 flag is set on a page,
  * indicating that the folio has other metadata associated with it.
  *
  * The @gfp argument specifies whether I/O may be performed to release
  * this page (__GFP_IO), and whether the call may block
  * (__GFP_RECLAIM & __GFP_FS).
  *
  * Return: %true if the release was successful, otherwise %false.
  */
 bool filemap_release_folio(struct folio *folio, gfp_t gfp)
 {
     struct address_space * const mapping = folio->mapping;
 
     BUG_ON(!folio_test_locked(folio));
     if (folio_test_writeback(folio))
         return false;
 
     if (mapping && mapping->a_ops->release_folio)
         return mapping->a_ops->release_folio(folio, gfp);
     return try_to_free_buffers(folio);
 }
 EXPORT_SYMBOL(filemap_release_folio);