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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2010 Red Hat, Inc.
  * Copyright (C) 2016-2019 Christoph Hellwig.
  */
 #include <linux/module.h>
 #include <linux/compiler.h>
 #include <linux/fs.h>
 #include <linux/iomap.h>
 #include <linux/pagemap.h>
 #include <linux/uio.h>
 #include <linux/buffer_head.h>
 #include <linux/dax.h>
 #include <linux/writeback.h>
 #include <linux/list_sort.h>
 #include <linux/swap.h>
 #include <linux/bio.h>
 #include <linux/sched/signal.h>
 #include <linux/migrate.h>
 #include "trace.h"
 
 #include "../internal.h"
 
 #define IOEND_BATCH_SIZE    4096
 
 /*
  * Structure allocated for each folio when block size < folio size
  * to track sub-folio uptodate status and I/O completions.
  */
 struct iomap_page {
     atomic_t        read_bytes_pending;
     atomic_t        write_bytes_pending;
     spinlock_t      uptodate_lock;
     unsigned long       uptodate[];
 };
 
 static inline struct iomap_page *to_iomap_page(struct folio *folio)
 {
     if (folio_test_private(folio))
         return folio_get_private(folio);
     return NULL;
 }
 
 static struct bio_set iomap_ioend_bioset;
 
 static struct iomap_page *
 iomap_page_create(struct inode *inode, struct folio *folio, unsigned int flags)
 {
     struct iomap_page *iop = to_iomap_page(folio);
     unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
     gfp_t gfp;
 
     if (iop || nr_blocks <= 1)
         return iop;
 
     if (flags & IOMAP_NOWAIT)
         gfp = GFP_NOWAIT;
     else
         gfp = GFP_NOFS | __GFP_NOFAIL;
 
     iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),
               gfp);
     if (iop) {
         spin_lock_init(&iop->uptodate_lock);
         if (folio_test_uptodate(folio))
             bitmap_fill(iop->uptodate, nr_blocks);
         folio_attach_private(folio, iop);
     }
     return iop;
 }
 
 static void iomap_page_release(struct folio *folio)
 {
     struct iomap_page *iop = folio_detach_private(folio);
     struct inode *inode = folio->mapping->host;
     unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
 
     if (!iop)
         return;
     WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
     WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
     WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
             folio_test_uptodate(folio));
     kfree(iop);
 }
 
 /*
  * Calculate the range inside the folio that we actually need to read.
  */
 static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
         loff_t *pos, loff_t length, size_t *offp, size_t *lenp)
 {
     struct iomap_page *iop = to_iomap_page(folio);
     loff_t orig_pos = *pos;
     loff_t isize = i_size_read(inode);
     unsigned block_bits = inode->i_blkbits;
     unsigned block_size = (1 << block_bits);
     size_t poff = offset_in_folio(folio, *pos);
     size_t plen = min_t(loff_t, folio_size(folio) - poff, length);
     unsigned first = poff >> block_bits;
     unsigned last = (poff + plen - 1) >> block_bits;
 
     /*
      * If the block size is smaller than the page size, we need to check the
      * per-block uptodate status and adjust the offset and length if needed
      * to avoid reading in already uptodate ranges.
      */
     if (iop) {
         unsigned int i;
 
         /* move forward for each leading block marked uptodate */
         for (i = first; i <= last; i++) {
             if (!test_bit(i, iop->uptodate))
                 break;
             *pos += block_size;
             poff += block_size;
             plen -= block_size;
             first++;
         }
 
         /* truncate len if we find any trailing uptodate block(s) */
         for ( ; i <= last; i++) {
             if (test_bit(i, iop->uptodate)) {
                 plen -= (last - i + 1) * block_size;
                 last = i - 1;
                 break;
             }
         }
     }
 
     /*
      * If the extent spans the block that contains the i_size, we need to
      * handle both halves separately so that we properly zero data in the
      * page cache for blocks that are entirely outside of i_size.
      */
     if (orig_pos <= isize && orig_pos + length > isize) {
         unsigned end = offset_in_folio(folio, isize - 1) >> block_bits;
 
         if (first <= end && last > end)
             plen -= (last - end) * block_size;
     }
 
     *offp = poff;
     *lenp = plen;
 }
 
 static void iomap_iop_set_range_uptodate(struct folio *folio,
         struct iomap_page *iop, size_t off, size_t len)
 {
     struct inode *inode = folio->mapping->host;
     unsigned first = off >> inode->i_blkbits;
     unsigned last = (off + len - 1) >> inode->i_blkbits;
     unsigned long flags;
 
     spin_lock_irqsave(&iop->uptodate_lock, flags);
     bitmap_set(iop->uptodate, first, last - first + 1);
     if (bitmap_full(iop->uptodate, i_blocks_per_folio(inode, folio)))
         folio_mark_uptodate(folio);
     spin_unlock_irqrestore(&iop->uptodate_lock, flags);
 }
 
 static void iomap_set_range_uptodate(struct folio *folio,
         struct iomap_page *iop, size_t off, size_t len)
 {
     if (iop)
         iomap_iop_set_range_uptodate(folio, iop, off, len);
     else
         folio_mark_uptodate(folio);
 }
 
 static void iomap_finish_folio_read(struct folio *folio, size_t offset,
         size_t len, int error)
 {
     struct iomap_page *iop = to_iomap_page(folio);
 
     if (unlikely(error)) {
         folio_clear_uptodate(folio);
         folio_set_error(folio);
     } else {
         iomap_set_range_uptodate(folio, iop, offset, len);
     }
 
     if (!iop || atomic_sub_and_test(len, &iop->read_bytes_pending))
         folio_unlock(folio);
 }
 
 static void iomap_read_end_io(struct bio *bio)
 {
     int error = blk_status_to_errno(bio->bi_status);
     struct folio_iter fi;
 
     bio_for_each_folio_all(fi, bio)
         iomap_finish_folio_read(fi.folio, fi.offset, fi.length, error);
     bio_put(bio);
 }
 
 struct iomap_readpage_ctx {
     struct folio        *cur_folio;
     bool            cur_folio_in_bio;
     struct bio      *bio;
     struct readahead_control *rac;
 };
 
 /**
  * iomap_read_inline_data - copy inline data into the page cache
  * @iter: iteration structure
  * @folio: folio to copy to
  *
  * Copy the inline data in @iter into @folio and zero out the rest of the folio.
  * Only a single IOMAP_INLINE extent is allowed at the end of each file.
  * Returns zero for success to complete the read, or the usual negative errno.
  */
 static int iomap_read_inline_data(const struct iomap_iter *iter,
         struct folio *folio)
 {
     struct iomap_page *iop;
     const struct iomap *iomap = iomap_iter_srcmap(iter);
     size_t size = i_size_read(iter->inode) - iomap->offset;
     size_t poff = offset_in_page(iomap->offset);
     size_t offset = offset_in_folio(folio, iomap->offset);
     void *addr;
 
     if (folio_test_uptodate(folio))
         return 0;
 
     if (WARN_ON_ONCE(size > PAGE_SIZE - poff))
         return -EIO;
     if (WARN_ON_ONCE(size > PAGE_SIZE -
              offset_in_page(iomap->inline_data)))
         return -EIO;
     if (WARN_ON_ONCE(size > iomap->length))
         return -EIO;
     if (offset > 0)
         iop = iomap_page_create(iter->inode, folio, iter->flags);
     else
         iop = to_iomap_page(folio);
 
     addr = kmap_local_folio(folio, offset);
     memcpy(addr, iomap->inline_data, size);
     memset(addr + size, 0, PAGE_SIZE - poff - size);
     kunmap_local(addr);
     iomap_set_range_uptodate(folio, iop, offset, PAGE_SIZE - poff);
     return 0;
 }
 
 static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
         loff_t pos)
 {
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
 
     return srcmap->type != IOMAP_MAPPED ||
         (srcmap->flags & IOMAP_F_NEW) ||
         pos >= i_size_read(iter->inode);
 }
 
 static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
         struct iomap_readpage_ctx *ctx, loff_t offset)
 {
     const struct iomap *iomap = &iter->iomap;
     loff_t pos = iter->pos + offset;
     loff_t length = iomap_length(iter) - offset;
     struct folio *folio = ctx->cur_folio;
     struct iomap_page *iop;
     loff_t orig_pos = pos;
     size_t poff, plen;
     sector_t sector;
 
     if (iomap->type == IOMAP_INLINE)
         return iomap_read_inline_data(iter, folio);
 
     /* zero post-eof blocks as the page may be mapped */
     iop = iomap_page_create(iter->inode, folio, iter->flags);
     iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff, &plen);
     if (plen == 0)
         goto done;
 
     if (iomap_block_needs_zeroing(iter, pos)) {
         folio_zero_range(folio, poff, plen);
         iomap_set_range_uptodate(folio, iop, poff, plen);
         goto done;
     }
 
     ctx->cur_folio_in_bio = true;
     if (iop)
         atomic_add(plen, &iop->read_bytes_pending);
 
     sector = iomap_sector(iomap, pos);
     if (!ctx->bio ||
         bio_end_sector(ctx->bio) != sector ||
         !bio_add_folio(ctx->bio, folio, plen, poff)) {
         gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
         gfp_t orig_gfp = gfp;
         unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
 
         if (ctx->bio)
             submit_bio(ctx->bio);
 
         if (ctx->rac) /* same as readahead_gfp_mask */
             gfp |= __GFP_NORETRY | __GFP_NOWARN;
         ctx->bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs),
                      REQ_OP_READ, gfp);
         /*
          * If the bio_alloc fails, try it again for a single page to
          * avoid having to deal with partial page reads.  This emulates
          * what do_mpage_read_folio does.
          */
         if (!ctx->bio) {
             ctx->bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ,
                          orig_gfp);
         }
         if (ctx->rac)
             ctx->bio->bi_opf |= REQ_RAHEAD;
         ctx->bio->bi_iter.bi_sector = sector;
         ctx->bio->bi_end_io = iomap_read_end_io;
         bio_add_folio(ctx->bio, folio, plen, poff);
     }
 
 done:
     /*
      * Move the caller beyond our range so that it keeps making progress.
      * For that, we have to include any leading non-uptodate ranges, but
      * we can skip trailing ones as they will be handled in the next
      * iteration.
      */
     return pos - orig_pos + plen;
 }
 
 int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = folio->mapping->host,
         .pos        = folio_pos(folio),
         .len        = folio_size(folio),
     };
     struct iomap_readpage_ctx ctx = {
         .cur_folio  = folio,
     };
     int ret;
 
     trace_iomap_readpage(iter.inode, 1);
 
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = iomap_readpage_iter(&iter, &ctx, 0);
 
     if (ret < 0)
         folio_set_error(folio);
 
     if (ctx.bio) {
         submit_bio(ctx.bio);
         WARN_ON_ONCE(!ctx.cur_folio_in_bio);
     } else {
         WARN_ON_ONCE(ctx.cur_folio_in_bio);
         folio_unlock(folio);
     }
 
     /*
      * Just like mpage_readahead and block_read_full_folio, we always
      * return 0 and just set the folio error flag on errors.  This
      * should be cleaned up throughout the stack eventually.
      */
     return 0;
 }
 EXPORT_SYMBOL_GPL(iomap_read_folio);
 
 static loff_t iomap_readahead_iter(const struct iomap_iter *iter,
         struct iomap_readpage_ctx *ctx)
 {
     loff_t length = iomap_length(iter);
     loff_t done, ret;
 
     for (done = 0; done < length; done += ret) {
         if (ctx->cur_folio &&
             offset_in_folio(ctx->cur_folio, iter->pos + done) == 0) {
             if (!ctx->cur_folio_in_bio)
                 folio_unlock(ctx->cur_folio);
             ctx->cur_folio = NULL;
         }
         if (!ctx->cur_folio) {
             ctx->cur_folio = readahead_folio(ctx->rac);
             ctx->cur_folio_in_bio = false;
         }
         ret = iomap_readpage_iter(iter, ctx, done);
         if (ret <= 0)
             return ret;
     }
 
     return done;
 }
 
 /**
  * iomap_readahead - Attempt to read pages from a file.
  * @rac: Describes the pages to be read.
  * @ops: The operations vector for the filesystem.
  *
  * This function is for filesystems to call to implement their readahead
  * address_space operation.
  *
  * Context: The @ops callbacks may submit I/O (eg to read the addresses of
  * blocks from disc), and may wait for it.  The caller may be trying to
  * access a different page, and so sleeping excessively should be avoided.
  * It may allocate memory, but should avoid costly allocations.  This
  * function is called with memalloc_nofs set, so allocations will not cause
  * the filesystem to be reentered.
  */
 void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode  = rac->mapping->host,
         .pos    = readahead_pos(rac),
         .len    = readahead_length(rac),
     };
     struct iomap_readpage_ctx ctx = {
         .rac    = rac,
     };
 
     trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
 
     while (iomap_iter(&iter, ops) > 0)
         iter.processed = iomap_readahead_iter(&iter, &ctx);
 
     if (ctx.bio)
         submit_bio(ctx.bio);
     if (ctx.cur_folio) {
         if (!ctx.cur_folio_in_bio)
             folio_unlock(ctx.cur_folio);
     }
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
 
 /*
  * iomap_is_partially_uptodate checks whether blocks within a folio are
  * uptodate or not.
  *
  * Returns true if all blocks which correspond to the specified part
  * of the folio are uptodate.
  */
 bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 {
     struct iomap_page *iop = to_iomap_page(folio);
     struct inode *inode = folio->mapping->host;
     unsigned first, last, i;
 
     if (!iop)
         return false;
 
     /* Caller's range may extend past the end of this folio */
     count = min(folio_size(folio) - from, count);
 
     /* First and last blocks in range within folio */
     first = from >> inode->i_blkbits;
     last = (from + count - 1) >> inode->i_blkbits;
 
     for (i = first; i <= last; i++)
         if (!test_bit(i, iop->uptodate))
             return false;
     return true;
 }
 EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
 
 bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags)
 {
     trace_iomap_release_folio(folio->mapping->host, folio_pos(folio),
             folio_size(folio));
 
     /*
      * mm accommodates an old ext3 case where clean folios might
      * not have had the dirty bit cleared.  Thus, it can send actual
      * dirty folios to ->release_folio() via shrink_active_list();
      * skip those here.
      */
     if (folio_test_dirty(folio) || folio_test_writeback(folio))
         return false;
     iomap_page_release(folio);
     return true;
 }
 EXPORT_SYMBOL_GPL(iomap_release_folio);
 
 void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len)
 {
     trace_iomap_invalidate_folio(folio->mapping->host,
                     folio_pos(folio) + offset, len);
 
     /*
      * If we're invalidating the entire folio, clear the dirty state
      * from it and release it to avoid unnecessary buildup of the LRU.
      */
     if (offset == 0 && len == folio_size(folio)) {
         WARN_ON_ONCE(folio_test_writeback(folio));
         folio_cancel_dirty(folio);
         iomap_page_release(folio);
     } else if (folio_test_large(folio)) {
         /* Must release the iop so the page can be split */
         WARN_ON_ONCE(!folio_test_uptodate(folio) &&
                  folio_test_dirty(folio));
         iomap_page_release(folio);
     }
 }
 EXPORT_SYMBOL_GPL(iomap_invalidate_folio);
 
 static void
 iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
 {
     loff_t i_size = i_size_read(inode);
 
     /*
      * Only truncate newly allocated pages beyoned EOF, even if the
      * write started inside the existing inode size.
      */
     if (pos + len > i_size)
         truncate_pagecache_range(inode, max(pos, i_size),
                      pos + len - 1);
 }
 
 static int iomap_read_folio_sync(loff_t block_start, struct folio *folio,
         size_t poff, size_t plen, const struct iomap *iomap)
 {
     struct bio_vec bvec;
     struct bio bio;
 
     bio_init(&bio, iomap->bdev, &bvec, 1, REQ_OP_READ);
     bio.bi_iter.bi_sector = iomap_sector(iomap, block_start);
     bio_add_folio(&bio, folio, plen, poff);
     return submit_bio_wait(&bio);
 }
 
 static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
         size_t len, struct folio *folio)
 {
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     struct iomap_page *iop;
     loff_t block_size = i_blocksize(iter->inode);
     loff_t block_start = round_down(pos, block_size);
     loff_t block_end = round_up(pos + len, block_size);
     unsigned int nr_blocks = i_blocks_per_folio(iter->inode, folio);
     size_t from = offset_in_folio(folio, pos), to = from + len;
     size_t poff, plen;
 
     if (folio_test_uptodate(folio))
         return 0;
     folio_clear_error(folio);
 
     iop = iomap_page_create(iter->inode, folio, iter->flags);
     if ((iter->flags & IOMAP_NOWAIT) && !iop && nr_blocks > 1)
         return -EAGAIN;
 
     do {
         iomap_adjust_read_range(iter->inode, folio, &block_start,
                 block_end - block_start, &poff, &plen);
         if (plen == 0)
             break;
 
         if (!(iter->flags & IOMAP_UNSHARE) &&
             (from <= poff || from >= poff + plen) &&
             (to <= poff || to >= poff + plen))
             continue;
 
         if (iomap_block_needs_zeroing(iter, block_start)) {
             if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE))
                 return -EIO;
             folio_zero_segments(folio, poff, from, to, poff + plen);
         } else {
             int status;
 
             if (iter->flags & IOMAP_NOWAIT)
                 return -EAGAIN;
 
             status = iomap_read_folio_sync(block_start, folio,
                     poff, plen, srcmap);
             if (status)
                 return status;
         }
         iomap_set_range_uptodate(folio, iop, poff, plen);
     } while ((block_start += plen) < block_end);
 
     return 0;
 }
 
 static int iomap_write_begin_inline(const struct iomap_iter *iter,
         struct folio *folio)
 {
     /* needs more work for the tailpacking case; disable for now */
     if (WARN_ON_ONCE(iomap_iter_srcmap(iter)->offset != 0))
         return -EIO;
     return iomap_read_inline_data(iter, folio);
 }
 
 static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
         size_t len, struct folio **foliop)
 {
     const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     struct folio *folio;
     unsigned fgp = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE | FGP_NOFS;
     int status = 0;
 
     if (iter->flags & IOMAP_NOWAIT)
         fgp |= FGP_NOWAIT;
 
     BUG_ON(pos + len > iter->iomap.offset + iter->iomap.length);
     if (srcmap != &iter->iomap)
         BUG_ON(pos + len > srcmap->offset + srcmap->length);
 
     if (fatal_signal_pending(current))
         return -EINTR;
 
     if (!mapping_large_folio_support(iter->inode->i_mapping))
         len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
 
     if (page_ops && page_ops->page_prepare) {
         status = page_ops->page_prepare(iter->inode, pos, len);
         if (status)
             return status;
     }
 
     folio = __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
             fgp, mapping_gfp_mask(iter->inode->i_mapping));
     if (!folio) {
         status = (iter->flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOMEM;
         goto out_no_page;
     }
     if (pos + len > folio_pos(folio) + folio_size(folio))
         len = folio_pos(folio) + folio_size(folio) - pos;
 
     if (srcmap->type == IOMAP_INLINE)
         status = iomap_write_begin_inline(iter, folio);
     else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
         status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
     else
         status = __iomap_write_begin(iter, pos, len, folio);
 
     if (unlikely(status))
         goto out_unlock;
 
     *foliop = folio;
     return 0;
 
 out_unlock:
     folio_unlock(folio);
     folio_put(folio);
     iomap_write_failed(iter->inode, pos, len);
 
 out_no_page:
     if (page_ops && page_ops->page_done)
         page_ops->page_done(iter->inode, pos, 0, NULL);
     return status;
 }
 
 static size_t __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
         size_t copied, struct folio *folio)
 {
     struct iomap_page *iop = to_iomap_page(folio);
     flush_dcache_folio(folio);
 
     /*
      * The blocks that were entirely written will now be uptodate, so we
      * don't have to worry about a read_folio reading them and overwriting a
      * partial write.  However, if we've encountered a short write and only
      * partially written into a block, it will not be marked uptodate, so a
      * read_folio might come in and destroy our partial write.
      *
      * Do the simplest thing and just treat any short write to a
      * non-uptodate page as a zero-length write, and force the caller to
      * redo the whole thing.
      */
     if (unlikely(copied < len && !folio_test_uptodate(folio)))
         return 0;
     iomap_set_range_uptodate(folio, iop, offset_in_folio(folio, pos), len);
     filemap_dirty_folio(inode->i_mapping, folio);
     return copied;
 }
 
 static size_t iomap_write_end_inline(const struct iomap_iter *iter,
         struct folio *folio, loff_t pos, size_t copied)
 {
     const struct iomap *iomap = &iter->iomap;
     void *addr;
 
     WARN_ON_ONCE(!folio_test_uptodate(folio));
     BUG_ON(!iomap_inline_data_valid(iomap));
 
     flush_dcache_folio(folio);
     addr = kmap_local_folio(folio, pos);
     memcpy(iomap_inline_data(iomap, pos), addr, copied);
     kunmap_local(addr);
 
     mark_inode_dirty(iter->inode);
     return copied;
 }
 
 /* Returns the number of bytes copied.  May be 0.  Cannot be an errno. */
 static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
         size_t copied, struct folio *folio)
 {
     const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     loff_t old_size = iter->inode->i_size;
     size_t ret;
 
     if (srcmap->type == IOMAP_INLINE) {
         ret = iomap_write_end_inline(iter, folio, pos, copied);
     } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
         ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
                 copied, &folio->page, NULL);
     } else {
         ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
     }
 
     /*
      * Update the in-memory inode size after copying the data into the page
      * cache.  It's up to the file system to write the updated size to disk,
      * preferably after I/O completion so that no stale data is exposed.
      */
     if (pos + ret > old_size) {
         i_size_write(iter->inode, pos + ret);
         iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
     }
     folio_unlock(folio);
 
     if (old_size < pos)
         pagecache_isize_extended(iter->inode, old_size, pos);
     if (page_ops && page_ops->page_done)
         page_ops->page_done(iter->inode, pos, ret, &folio->page);
     folio_put(folio);
 
     if (ret < len)
         iomap_write_failed(iter->inode, pos + ret, len - ret);
     return ret;
 }
 
 static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 {
     loff_t length = iomap_length(iter);
     loff_t pos = iter->pos;
     ssize_t written = 0;
     long status = 0;
     struct address_space *mapping = iter->inode->i_mapping;
     unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0;
 
     do {
         struct folio *folio;
         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 */
 
         offset = offset_in_page(pos);
         bytes = min_t(unsigned long, PAGE_SIZE - offset,
                         iov_iter_count(i));
 again:
         status = balance_dirty_pages_ratelimited_flags(mapping,
                                    bdp_flags);
         if (unlikely(status))
             break;
 
         if (bytes > length)
             bytes = length;
 
         /*
          * Bring in the user page that we'll 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.
          *
          * For async buffered writes the assumption is that the user
          * page has already been faulted in. This can be optimized by
          * faulting the user page.
          */
         if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
             status = -EFAULT;
             break;
         }
 
         status = iomap_write_begin(iter, pos, bytes, &folio);
         if (unlikely(status))
             break;
 
         page = folio_file_page(folio, pos >> PAGE_SHIFT);
         if (mapping_writably_mapped(mapping))
             flush_dcache_page(page);
 
         copied = copy_page_from_iter_atomic(page, offset, bytes, i);
 
         status = iomap_write_end(iter, pos, bytes, copied, folio);
 
         if (unlikely(copied != status))
             iov_iter_revert(i, copied - status);
 
         cond_resched();
         if (unlikely(status == 0)) {
             /*
              * A short copy made iomap_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;
         length -= status;
     } while (iov_iter_count(i) && length);
 
     if (status == -EAGAIN) {
         iov_iter_revert(i, written);
         return -EAGAIN;
     }
     return written ? written : status;
 }
 
 ssize_t
 iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
         const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = iocb->ki_filp->f_mapping->host,
         .pos        = iocb->ki_pos,
         .len        = iov_iter_count(i),
         .flags      = IOMAP_WRITE,
     };
     int ret;
 
     if (iocb->ki_flags & IOCB_NOWAIT)
         iter.flags |= IOMAP_NOWAIT;
 
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = iomap_write_iter(&iter, i);
     if (iter.pos == iocb->ki_pos)
         return ret;
     return iter.pos - iocb->ki_pos;
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);
 
 static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 {
     struct iomap *iomap = &iter->iomap;
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     loff_t pos = iter->pos;
     loff_t length = iomap_length(iter);
     long status = 0;
     loff_t written = 0;
 
     /* don't bother with blocks that are not shared to start with */
     if (!(iomap->flags & IOMAP_F_SHARED))
         return length;
     /* don't bother with holes or unwritten extents */
     if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
         return length;
 
     do {
         unsigned long offset = offset_in_page(pos);
         unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length);
         struct folio *folio;
 
         status = iomap_write_begin(iter, pos, bytes, &folio);
         if (unlikely(status))
             return status;
 
         status = iomap_write_end(iter, pos, bytes, bytes, folio);
         if (WARN_ON_ONCE(status == 0))
             return -EIO;
 
         cond_resched();
 
         pos += status;
         written += status;
         length -= status;
 
         balance_dirty_pages_ratelimited(iter->inode->i_mapping);
     } while (length);
 
     return written;
 }
 
 int
 iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
         const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = inode,
         .pos        = pos,
         .len        = len,
         .flags      = IOMAP_WRITE | IOMAP_UNSHARE,
     };
     int ret;
 
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = iomap_unshare_iter(&iter);
     return ret;
 }
 EXPORT_SYMBOL_GPL(iomap_file_unshare);
 
 static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 {
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     loff_t pos = iter->pos;
     loff_t length = iomap_length(iter);
     loff_t written = 0;
 
     /* already zeroed?  we're done. */
     if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
         return length;
 
     do {
         struct folio *folio;
         int status;
         size_t offset;
         size_t bytes = min_t(u64, SIZE_MAX, length);
 
         status = iomap_write_begin(iter, pos, bytes, &folio);
         if (status)
             return status;
 
         offset = offset_in_folio(folio, pos);
         if (bytes > folio_size(folio) - offset)
             bytes = folio_size(folio) - offset;
 
         folio_zero_range(folio, offset, bytes);
         folio_mark_accessed(folio);
 
         bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
         if (WARN_ON_ONCE(bytes == 0))
             return -EIO;
 
         pos += bytes;
         length -= bytes;
         written += bytes;
     } while (length > 0);
 
     if (did_zero)
         *did_zero = true;
     return written;
 }
 
 int
 iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
         const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = inode,
         .pos        = pos,
         .len        = len,
         .flags      = IOMAP_ZERO,
     };
     int ret;
 
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = iomap_zero_iter(&iter, did_zero);
     return ret;
 }
 EXPORT_SYMBOL_GPL(iomap_zero_range);
 
 int
 iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
         const struct iomap_ops *ops)
 {
     unsigned int blocksize = i_blocksize(inode);
     unsigned int off = pos & (blocksize - 1);
 
     /* Block boundary? Nothing to do */
     if (!off)
         return 0;
     return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops);
 }
 EXPORT_SYMBOL_GPL(iomap_truncate_page);
 
 static loff_t iomap_folio_mkwrite_iter(struct iomap_iter *iter,
         struct folio *folio)
 {
     loff_t length = iomap_length(iter);
     int ret;
 
     if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
         ret = __block_write_begin_int(folio, iter->pos, length, NULL,
                           &iter->iomap);
         if (ret)
             return ret;
         block_commit_write(&folio->page, 0, length);
     } else {
         WARN_ON_ONCE(!folio_test_uptodate(folio));
         folio_mark_dirty(folio);
     }
 
     return length;
 }
 
 vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = file_inode(vmf->vma->vm_file),
         .flags      = IOMAP_WRITE | IOMAP_FAULT,
     };
     struct folio *folio = page_folio(vmf->page);
     ssize_t ret;
 
     folio_lock(folio);
     ret = folio_mkwrite_check_truncate(folio, iter.inode);
     if (ret < 0)
         goto out_unlock;
     iter.pos = folio_pos(folio);
     iter.len = ret;
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = iomap_folio_mkwrite_iter(&iter, folio);
 
     if (ret < 0)
         goto out_unlock;
     folio_wait_stable(folio);
     return VM_FAULT_LOCKED;
 out_unlock:
     folio_unlock(folio);
     return block_page_mkwrite_return(ret);
 }
 EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
 
 static void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
         size_t len, int error)
 {
     struct iomap_page *iop = to_iomap_page(folio);
 
     if (error) {
         folio_set_error(folio);
         mapping_set_error(inode->i_mapping, error);
     }
 
     WARN_ON_ONCE(i_blocks_per_folio(inode, folio) > 1 && !iop);
     WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) <= 0);
 
     if (!iop || atomic_sub_and_test(len, &iop->write_bytes_pending))
         folio_end_writeback(folio);
 }
 
 /*
  * We're now finished for good with this ioend structure.  Update the page
  * state, release holds on bios, and finally free up memory.  Do not use the
  * ioend after this.
  */
 static u32
 iomap_finish_ioend(struct iomap_ioend *ioend, int error)
 {
     struct inode *inode = ioend->io_inode;
     struct bio *bio = &ioend->io_inline_bio;
     struct bio *last = ioend->io_bio, *next;
     u64 start = bio->bi_iter.bi_sector;
     loff_t offset = ioend->io_offset;
     bool quiet = bio_flagged(bio, BIO_QUIET);
     u32 folio_count = 0;
 
     for (bio = &ioend->io_inline_bio; bio; bio = next) {
         struct folio_iter fi;
 
         /*
          * For the last bio, bi_private points to the ioend, so we
          * need to explicitly end the iteration here.
          */
         if (bio == last)
             next = NULL;
         else
             next = bio->bi_private;
 
         /* walk all folios in bio, ending page IO on them */
         bio_for_each_folio_all(fi, bio) {
             iomap_finish_folio_write(inode, fi.folio, fi.length,
                     error);
             folio_count++;
         }
         bio_put(bio);
     }
     /* The ioend has been freed by bio_put() */
 
     if (unlikely(error && !quiet)) {
         printk_ratelimited(KERN_ERR
 "%s: writeback error on inode %lu, offset %lld, sector %llu",
             inode->i_sb->s_id, inode->i_ino, offset, start);
     }
     return folio_count;
 }
 
 /*
  * Ioend completion routine for merged bios. This can only be called from task
  * contexts as merged ioends can be of unbound length. Hence we have to break up
  * the writeback completions into manageable chunks to avoid long scheduler
  * holdoffs. We aim to keep scheduler holdoffs down below 10ms so that we get
  * good batch processing throughput without creating adverse scheduler latency
  * conditions.
  */
 void
 iomap_finish_ioends(struct iomap_ioend *ioend, int error)
 {
     struct list_head tmp;
     u32 completions;
 
     might_sleep();
 
     list_replace_init(&ioend->io_list, &tmp);
     completions = iomap_finish_ioend(ioend, error);
 
     while (!list_empty(&tmp)) {
         if (completions > IOEND_BATCH_SIZE * 8) {
             cond_resched();
             completions = 0;
         }
         ioend = list_first_entry(&tmp, struct iomap_ioend, io_list);
         list_del_init(&ioend->io_list);
         completions += iomap_finish_ioend(ioend, error);
     }
 }
 EXPORT_SYMBOL_GPL(iomap_finish_ioends);
 
 /*
  * We can merge two adjacent ioends if they have the same set of work to do.
  */
 static bool
 iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
 {
     if (ioend->io_bio->bi_status != next->io_bio->bi_status)
         return false;
     if ((ioend->io_flags & IOMAP_F_SHARED) ^
         (next->io_flags & IOMAP_F_SHARED))
         return false;
     if ((ioend->io_type == IOMAP_UNWRITTEN) ^
         (next->io_type == IOMAP_UNWRITTEN))
         return false;
     if (ioend->io_offset + ioend->io_size != next->io_offset)
         return false;
     /*
      * Do not merge physically discontiguous ioends. The filesystem
      * completion functions will have to iterate the physical
      * discontiguities even if we merge the ioends at a logical level, so
      * we don't gain anything by merging physical discontiguities here.
      *
      * We cannot use bio->bi_iter.bi_sector here as it is modified during
      * submission so does not point to the start sector of the bio at
      * completion.
      */
     if (ioend->io_sector + (ioend->io_size >> 9) != next->io_sector)
         return false;
     return true;
 }
 
 void
 iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends)
 {
     struct iomap_ioend *next;
 
     INIT_LIST_HEAD(&ioend->io_list);
 
     while ((next = list_first_entry_or_null(more_ioends, struct iomap_ioend,
             io_list))) {
         if (!iomap_ioend_can_merge(ioend, next))
             break;
         list_move_tail(&next->io_list, &ioend->io_list);
         ioend->io_size += next->io_size;
     }
 }
 EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
 
 static int
 iomap_ioend_compare(void *priv, const struct list_head *a,
         const struct list_head *b)
 {
     struct iomap_ioend *ia = container_of(a, struct iomap_ioend, io_list);
     struct iomap_ioend *ib = container_of(b, struct iomap_ioend, io_list);
 
     if (ia->io_offset < ib->io_offset)
         return -1;
     if (ia->io_offset > ib->io_offset)
         return 1;
     return 0;
 }
 
 void
 iomap_sort_ioends(struct list_head *ioend_list)
 {
     list_sort(NULL, ioend_list, iomap_ioend_compare);
 }
 EXPORT_SYMBOL_GPL(iomap_sort_ioends);
 
 static void iomap_writepage_end_bio(struct bio *bio)
 {
     struct iomap_ioend *ioend = bio->bi_private;
 
     iomap_finish_ioend(ioend, blk_status_to_errno(bio->bi_status));
 }
 
 /*
  * Submit the final bio for an ioend.
  *
  * If @error is non-zero, it means that we have a situation where some part of
  * the submission process has failed after we've marked pages for writeback
  * and unlocked them.  In this situation, we need to fail the bio instead of
  * submitting it.  This typically only happens on a filesystem shutdown.
  */
 static int
 iomap_submit_ioend(struct iomap_writepage_ctx *wpc, struct iomap_ioend *ioend,
         int error)
 {
     ioend->io_bio->bi_private = ioend;
     ioend->io_bio->bi_end_io = iomap_writepage_end_bio;
 
     if (wpc->ops->prepare_ioend)
         error = wpc->ops->prepare_ioend(ioend, error);
     if (error) {
         /*
          * If we're failing the IO now, just mark the ioend with an
          * error and finish it.  This will run IO completion immediately
          * as there is only one reference to the ioend at this point in
          * time.
          */
         ioend->io_bio->bi_status = errno_to_blk_status(error);
         bio_endio(ioend->io_bio);
         return error;
     }
 
     submit_bio(ioend->io_bio);
     return 0;
 }
 
 static struct iomap_ioend *
 iomap_alloc_ioend(struct inode *inode, struct iomap_writepage_ctx *wpc,
         loff_t offset, sector_t sector, struct writeback_control *wbc)
 {
     struct iomap_ioend *ioend;
     struct bio *bio;
 
     bio = bio_alloc_bioset(wpc->iomap.bdev, BIO_MAX_VECS,
                    REQ_OP_WRITE | wbc_to_write_flags(wbc),
                    GFP_NOFS, &iomap_ioend_bioset);
     bio->bi_iter.bi_sector = sector;
     wbc_init_bio(wbc, bio);
 
     ioend = container_of(bio, struct iomap_ioend, io_inline_bio);
     INIT_LIST_HEAD(&ioend->io_list);
     ioend->io_type = wpc->iomap.type;
     ioend->io_flags = wpc->iomap.flags;
     ioend->io_inode = inode;
     ioend->io_size = 0;
     ioend->io_folios = 0;
     ioend->io_offset = offset;
     ioend->io_bio = bio;
     ioend->io_sector = sector;
     return ioend;
 }
 
 /*
  * Allocate a new bio, and chain the old bio to the new one.
  *
  * Note that we have to perform the chaining in this unintuitive order
  * so that the bi_private linkage is set up in the right direction for the
  * traversal in iomap_finish_ioend().
  */
 static struct bio *
 iomap_chain_bio(struct bio *prev)
 {
     struct bio *new;
 
     new = bio_alloc(prev->bi_bdev, BIO_MAX_VECS, prev->bi_opf, GFP_NOFS);
     bio_clone_blkg_association(new, prev);
     new->bi_iter.bi_sector = bio_end_sector(prev);
 
     bio_chain(prev, new);
     bio_get(prev);      /* for iomap_finish_ioend */
     submit_bio(prev);
     return new;
 }
 
 static bool
 iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t offset,
         sector_t sector)
 {
     if ((wpc->iomap.flags & IOMAP_F_SHARED) !=
         (wpc->ioend->io_flags & IOMAP_F_SHARED))
         return false;
     if (wpc->iomap.type != wpc->ioend->io_type)
         return false;
     if (offset != wpc->ioend->io_offset + wpc->ioend->io_size)
         return false;
     if (sector != bio_end_sector(wpc->ioend->io_bio))
         return false;
     /*
      * Limit ioend bio chain lengths to minimise IO completion latency. This
      * also prevents long tight loops ending page writeback on all the
      * folios in the ioend.
      */
     if (wpc->ioend->io_folios >= IOEND_BATCH_SIZE)
         return false;
     return true;
 }
 
 /*
  * Test to see if we have an existing ioend structure that we could append to
  * first; otherwise finish off the current ioend and start another.
  */
 static void
 iomap_add_to_ioend(struct inode *inode, loff_t pos, struct folio *folio,
         struct iomap_page *iop, struct iomap_writepage_ctx *wpc,
         struct writeback_control *wbc, struct list_head *iolist)
 {
     sector_t sector = iomap_sector(&wpc->iomap, pos);
     unsigned len = i_blocksize(inode);
     size_t poff = offset_in_folio(folio, pos);
 
     if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos, sector)) {
         if (wpc->ioend)
             list_add(&wpc->ioend->io_list, iolist);
         wpc->ioend = iomap_alloc_ioend(inode, wpc, pos, sector, wbc);
     }
 
     if (!bio_add_folio(wpc->ioend->io_bio, folio, len, poff)) {
         wpc->ioend->io_bio = iomap_chain_bio(wpc->ioend->io_bio);
         bio_add_folio(wpc->ioend->io_bio, folio, len, poff);
     }
 
     if (iop)
         atomic_add(len, &iop->write_bytes_pending);
     wpc->ioend->io_size += len;
     wbc_account_cgroup_owner(wbc, &folio->page, len);
 }
 
 /*
  * We implement an immediate ioend submission policy here to avoid needing to
  * chain multiple ioends and hence nest mempool allocations which can violate
  * the forward progress guarantees we need to provide. The current ioend we're
  * adding blocks to is cached in the writepage context, and if the new block
  * doesn't append to the cached ioend, it will create a new ioend and cache that
  * instead.
  *
  * If a new ioend is created and cached, the old ioend is returned and queued
  * locally for submission once the entire page is processed or an error has been
  * detected.  While ioends are submitted immediately after they are completed,
  * batching optimisations are provided by higher level block plugging.
  *
  * At the end of a writeback pass, there will be a cached ioend remaining on the
  * writepage context that the caller will need to submit.
  */
 static int
 iomap_writepage_map(struct iomap_writepage_ctx *wpc,
         struct writeback_control *wbc, struct inode *inode,
         struct folio *folio, u64 end_pos)
 {
     struct iomap_page *iop = iomap_page_create(inode, folio, 0);
     struct iomap_ioend *ioend, *next;
     unsigned len = i_blocksize(inode);
     unsigned nblocks = i_blocks_per_folio(inode, folio);
     u64 pos = folio_pos(folio);
     int error = 0, count = 0, i;
     LIST_HEAD(submit_list);
 
     WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
 
     /*
      * Walk through the folio to find areas to write back. If we
      * run off the end of the current map or find the current map
      * invalid, grab a new one.
      */
     for (i = 0; i < nblocks && pos < end_pos; i++, pos += len) {
         if (iop && !test_bit(i, iop->uptodate))
             continue;
 
         error = wpc->ops->map_blocks(wpc, inode, pos);
         if (error)
             break;
         if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
             continue;
         if (wpc->iomap.type == IOMAP_HOLE)
             continue;
         iomap_add_to_ioend(inode, pos, folio, iop, wpc, wbc,
                  &submit_list);
         count++;
     }
     if (count)
         wpc->ioend->io_folios++;
 
     WARN_ON_ONCE(!wpc->ioend && !list_empty(&submit_list));
     WARN_ON_ONCE(!folio_test_locked(folio));
     WARN_ON_ONCE(folio_test_writeback(folio));
     WARN_ON_ONCE(folio_test_dirty(folio));
 
     /*
      * We cannot cancel the ioend directly here on error.  We may have
      * already set other pages under writeback and hence we have to run I/O
      * completion to mark the error state of the pages under writeback
      * appropriately.
      */
     if (unlikely(error)) {
         /*
          * Let the filesystem know what portion of the current page
          * failed to map. If the page hasn't been added to ioend, it
          * won't be affected by I/O completion and we must unlock it
          * now.
          */
         if (wpc->ops->discard_folio)
             wpc->ops->discard_folio(folio, pos);
         if (!count) {
             folio_unlock(folio);
             goto done;
         }
     }
 
     folio_start_writeback(folio);
     folio_unlock(folio);
 
     /*
      * Preserve the original error if there was one; catch
      * submission errors here and propagate into subsequent ioend
      * submissions.
      */
     list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
         int error2;
 
         list_del_init(&ioend->io_list);
         error2 = iomap_submit_ioend(wpc, ioend, error);
         if (error2 && !error)
             error = error2;
     }
 
     /*
      * We can end up here with no error and nothing to write only if we race
      * with a partial page truncate on a sub-page block sized filesystem.
      */
     if (!count)
         folio_end_writeback(folio);
 done:
     mapping_set_error(folio->mapping, error);
     return error;
 }
 
 /*
  * Write out a dirty page.
  *
  * For delalloc space on the page, we need to allocate space and flush it.
  * For unwritten space on the page, we need to start the conversion to
  * regular allocated space.
  */
 static int
 iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
 {
     struct folio *folio = page_folio(page);
     struct iomap_writepage_ctx *wpc = data;
     struct inode *inode = folio->mapping->host;
     u64 end_pos, isize;
 
     trace_iomap_writepage(inode, folio_pos(folio), folio_size(folio));
 
     /*
      * Refuse to write the folio out if we're called from reclaim context.
      *
      * This avoids stack overflows when called from deeply used stacks in
      * random callers for direct reclaim or memcg reclaim.  We explicitly
      * allow reclaim from kswapd as the stack usage there is relatively low.
      *
      * This should never happen except in the case of a VM regression so
      * warn about it.
      */
     if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
             PF_MEMALLOC))
         goto redirty;
 
     /*
      * Is this folio beyond the end of the file?
      *
      * The folio index is less than the end_index, adjust the end_pos
      * to the highest offset that this folio should represent.
      * -----------------------------------------------------
      * |            file mapping           | <EOF> |
      * -----------------------------------------------------
      * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
      * ^--------------------------------^----------|--------
      * |     desired writeback range    |      see else    |
      * ---------------------------------^------------------|
      */
     isize = i_size_read(inode);
     end_pos = folio_pos(folio) + folio_size(folio);
     if (end_pos > isize) {
         /*
          * Check whether the page to write out is beyond or straddles
          * i_size or not.
          * -------------------------------------------------------
          * |        file mapping                | <EOF>  |
          * -------------------------------------------------------
          * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
          * ^--------------------------------^-----------|---------
          * |                    |      Straddles     |
          * ---------------------------------^-----------|--------|
          */
         size_t poff = offset_in_folio(folio, isize);
         pgoff_t end_index = isize >> PAGE_SHIFT;
 
         /*
          * Skip the page if it's fully outside i_size, e.g.
          * due to a truncate operation that's in progress.  We've
          * cleaned this page and truncate will finish things off for
          * us.
          *
          * Note that the end_index is unsigned long.  If the given
          * offset is greater than 16TB on a 32-bit system then if we
          * checked if the page is fully outside i_size with
          * "if (page->index >= end_index + 1)", "end_index + 1" would
          * overflow and evaluate to 0.  Hence this page would be
          * redirtied and written out repeatedly, which would result in
          * an infinite loop; the user program performing this operation
          * would hang.  Instead, we can detect this situation by
          * checking if the page is totally beyond i_size or if its
          * offset is just equal to the EOF.
          */
         if (folio->index > end_index ||
             (folio->index == end_index && poff == 0))
             goto unlock;
 
         /*
          * The page straddles i_size.  It must be zeroed out on each
          * and every writepage invocation because it may be mmapped.
          * "A file is mapped in multiples of the page size.  For a file
          * that is not a multiple of the page size, the remaining
          * memory is zeroed when mapped, and writes to that region are
          * not written out to the file."
          */
         folio_zero_segment(folio, poff, folio_size(folio));
         end_pos = isize;
     }
 
     return iomap_writepage_map(wpc, wbc, inode, folio, end_pos);
 
 redirty:
     folio_redirty_for_writepage(wbc, folio);
 unlock:
     folio_unlock(folio);
     return 0;
 }
 
 int
 iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
         struct iomap_writepage_ctx *wpc,
         const struct iomap_writeback_ops *ops)
 {
     int         ret;
 
     wpc->ops = ops;
     ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
     if (!wpc->ioend)
         return ret;
     return iomap_submit_ioend(wpc, wpc->ioend, ret);
 }
 EXPORT_SYMBOL_GPL(iomap_writepages);
 
 static int __init iomap_init(void)
 {
     return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
                offsetof(struct iomap_ioend, io_inline_bio),
                BIOSET_NEED_BVECS);
 }
 fs_initcall(iomap_init);

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