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 // SPDX-License-Identifier: GPL-2.0+
 /*
  * linux/fs/jbd2/journal.c
  *
  * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
  *
  * Copyright 1998 Red Hat corp --- All Rights Reserved
  *
  * Generic filesystem journal-writing code; part of the ext2fs
  * journaling system.
  *
  * This file manages journals: areas of disk reserved for logging
  * transactional updates.  This includes the kernel journaling thread
  * which is responsible for scheduling updates to the log.
  *
  * We do not actually manage the physical storage of the journal in this
  * file: that is left to a per-journal policy function, which allows us
  * to store the journal within a filesystem-specified area for ext2
  * journaling (ext2 can use a reserved inode for storing the log).
  */
 
 #include <linux/module.h>
 #include <linux/time.h>
 #include <linux/fs.h>
 #include <linux/jbd2.h>
 #include <linux/errno.h>
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/freezer.h>
 #include <linux/pagemap.h>
 #include <linux/kthread.h>
 #include <linux/poison.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/math64.h>
 #include <linux/hash.h>
 #include <linux/log2.h>
 #include <linux/vmalloc.h>
 #include <linux/backing-dev.h>
 #include <linux/bitops.h>
 #include <linux/ratelimit.h>
 #include <linux/sched/mm.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/jbd2.h>
 
 #include <linux/uaccess.h>
 #include <asm/page.h>
 
 #ifdef CONFIG_JBD2_DEBUG
 static ushort jbd2_journal_enable_debug __read_mostly;
 
 module_param_named(jbd2_debug, jbd2_journal_enable_debug, ushort, 0644);
 MODULE_PARM_DESC(jbd2_debug, "Debugging level for jbd2");
 #endif
 
 EXPORT_SYMBOL(jbd2_journal_extend);
 EXPORT_SYMBOL(jbd2_journal_stop);
 EXPORT_SYMBOL(jbd2_journal_lock_updates);
 EXPORT_SYMBOL(jbd2_journal_unlock_updates);
 EXPORT_SYMBOL(jbd2_journal_get_write_access);
 EXPORT_SYMBOL(jbd2_journal_get_create_access);
 EXPORT_SYMBOL(jbd2_journal_get_undo_access);
 EXPORT_SYMBOL(jbd2_journal_set_triggers);
 EXPORT_SYMBOL(jbd2_journal_dirty_metadata);
 EXPORT_SYMBOL(jbd2_journal_forget);
 EXPORT_SYMBOL(jbd2_journal_flush);
 EXPORT_SYMBOL(jbd2_journal_revoke);
 
 EXPORT_SYMBOL(jbd2_journal_init_dev);
 EXPORT_SYMBOL(jbd2_journal_init_inode);
 EXPORT_SYMBOL(jbd2_journal_check_used_features);
 EXPORT_SYMBOL(jbd2_journal_check_available_features);
 EXPORT_SYMBOL(jbd2_journal_set_features);
 EXPORT_SYMBOL(jbd2_journal_load);
 EXPORT_SYMBOL(jbd2_journal_destroy);
 EXPORT_SYMBOL(jbd2_journal_abort);
 EXPORT_SYMBOL(jbd2_journal_errno);
 EXPORT_SYMBOL(jbd2_journal_ack_err);
 EXPORT_SYMBOL(jbd2_journal_clear_err);
 EXPORT_SYMBOL(jbd2_log_wait_commit);
 EXPORT_SYMBOL(jbd2_journal_start_commit);
 EXPORT_SYMBOL(jbd2_journal_force_commit_nested);
 EXPORT_SYMBOL(jbd2_journal_wipe);
 EXPORT_SYMBOL(jbd2_journal_blocks_per_page);
 EXPORT_SYMBOL(jbd2_journal_invalidate_folio);
 EXPORT_SYMBOL(jbd2_journal_try_to_free_buffers);
 EXPORT_SYMBOL(jbd2_journal_force_commit);
 EXPORT_SYMBOL(jbd2_journal_inode_ranged_write);
 EXPORT_SYMBOL(jbd2_journal_inode_ranged_wait);
 EXPORT_SYMBOL(jbd2_journal_submit_inode_data_buffers);
 EXPORT_SYMBOL(jbd2_journal_finish_inode_data_buffers);
 EXPORT_SYMBOL(jbd2_journal_init_jbd_inode);
 EXPORT_SYMBOL(jbd2_journal_release_jbd_inode);
 EXPORT_SYMBOL(jbd2_journal_begin_ordered_truncate);
 EXPORT_SYMBOL(jbd2_inode_cache);
 
 static int jbd2_journal_create_slab(size_t slab_size);
 
 #ifdef CONFIG_JBD2_DEBUG
 void __jbd2_debug(int level, const char *file, const char *func,
           unsigned int line, const char *fmt, ...)
 {
     struct va_format vaf;
     va_list args;
 
     if (level > jbd2_journal_enable_debug)
         return;
     va_start(args, fmt);
     vaf.fmt = fmt;
     vaf.va = &args;
     printk(KERN_DEBUG "%s: (%s, %u): %pV", file, func, line, &vaf);
     va_end(args);
 }
 #endif
 
 /* Checksumming functions */
 static int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
 {
     if (!jbd2_journal_has_csum_v2or3_feature(j))
         return 1;
 
     return sb->s_checksum_type == JBD2_CRC32C_CHKSUM;
 }
 
 static __be32 jbd2_superblock_csum(journal_t *j, journal_superblock_t *sb)
 {
     __u32 csum;
     __be32 old_csum;
 
     old_csum = sb->s_checksum;
     sb->s_checksum = 0;
     csum = jbd2_chksum(j, ~0, (char *)sb, sizeof(journal_superblock_t));
     sb->s_checksum = old_csum;
 
     return cpu_to_be32(csum);
 }
 
 /*
  * Helper function used to manage commit timeouts
  */
 
 static void commit_timeout(struct timer_list *t)
 {
     journal_t *journal = from_timer(journal, t, j_commit_timer);
 
     wake_up_process(journal->j_task);
 }
 
 /*
  * kjournald2: The main thread function used to manage a logging device
  * journal.
  *
  * This kernel thread is responsible for two things:
  *
  * 1) COMMIT:  Every so often we need to commit the current state of the
  *    filesystem to disk.  The journal thread is responsible for writing
  *    all of the metadata buffers to disk. If a fast commit is ongoing
  *    journal thread waits until it's done and then continues from
  *    there on.
  *
  * 2) CHECKPOINT: We cannot reuse a used section of the log file until all
  *    of the data in that part of the log has been rewritten elsewhere on
  *    the disk.  Flushing these old buffers to reclaim space in the log is
  *    known as checkpointing, and this thread is responsible for that job.
  */
 
 static int kjournald2(void *arg)
 {
     journal_t *journal = arg;
     transaction_t *transaction;
 
     /*
      * Set up an interval timer which can be used to trigger a commit wakeup
      * after the commit interval expires
      */
     timer_setup(&journal->j_commit_timer, commit_timeout, 0);
 
     set_freezable();
 
     /* Record that the journal thread is running */
     journal->j_task = current;
     wake_up(&journal->j_wait_done_commit);
 
     /*
      * Make sure that no allocations from this kernel thread will ever
      * recurse to the fs layer because we are responsible for the
      * transaction commit and any fs involvement might get stuck waiting for
      * the trasn. commit.
      */
     memalloc_nofs_save();
 
     /*
      * And now, wait forever for commit wakeup events.
      */
     write_lock(&journal->j_state_lock);
 
 loop:
     if (journal->j_flags & JBD2_UNMOUNT)
         goto end_loop;
 
     jbd2_debug(1, "commit_sequence=%u, commit_request=%u\n",
         journal->j_commit_sequence, journal->j_commit_request);
 
     if (journal->j_commit_sequence != journal->j_commit_request) {
         jbd2_debug(1, "OK, requests differ\n");
         write_unlock(&journal->j_state_lock);
         del_timer_sync(&journal->j_commit_timer);
         jbd2_journal_commit_transaction(journal);
         write_lock(&journal->j_state_lock);
         goto loop;
     }
 
     wake_up(&journal->j_wait_done_commit);
     if (freezing(current)) {
         /*
          * The simpler the better. Flushing journal isn't a
          * good idea, because that depends on threads that may
          * be already stopped.
          */
         jbd2_debug(1, "Now suspending kjournald2\n");
         write_unlock(&journal->j_state_lock);
         try_to_freeze();
         write_lock(&journal->j_state_lock);
     } else {
         /*
          * We assume on resume that commits are already there,
          * so we don't sleep
          */
         DEFINE_WAIT(wait);
         int should_sleep = 1;
 
         prepare_to_wait(&journal->j_wait_commit, &wait,
                 TASK_INTERRUPTIBLE);
         if (journal->j_commit_sequence != journal->j_commit_request)
             should_sleep = 0;
         transaction = journal->j_running_transaction;
         if (transaction && time_after_eq(jiffies,
                         transaction->t_expires))
             should_sleep = 0;
         if (journal->j_flags & JBD2_UNMOUNT)
             should_sleep = 0;
         if (should_sleep) {
             write_unlock(&journal->j_state_lock);
             schedule();
             write_lock(&journal->j_state_lock);
         }
         finish_wait(&journal->j_wait_commit, &wait);
     }
 
     jbd2_debug(1, "kjournald2 wakes\n");
 
     /*
      * Were we woken up by a commit wakeup event?
      */
     transaction = journal->j_running_transaction;
     if (transaction && time_after_eq(jiffies, transaction->t_expires)) {
         journal->j_commit_request = transaction->t_tid;
         jbd2_debug(1, "woke because of timeout\n");
     }
     goto loop;
 
 end_loop:
     del_timer_sync(&journal->j_commit_timer);
     journal->j_task = NULL;
     wake_up(&journal->j_wait_done_commit);
     jbd2_debug(1, "Journal thread exiting.\n");
     write_unlock(&journal->j_state_lock);
     return 0;
 }
 
 static int jbd2_journal_start_thread(journal_t *journal)
 {
     struct task_struct *t;
 
     t = kthread_run(kjournald2, journal, "jbd2/%s",
             journal->j_devname);
     if (IS_ERR(t))
         return PTR_ERR(t);
 
     wait_event(journal->j_wait_done_commit, journal->j_task != NULL);
     return 0;
 }
 
 static void journal_kill_thread(journal_t *journal)
 {
     write_lock(&journal->j_state_lock);
     journal->j_flags |= JBD2_UNMOUNT;
 
     while (journal->j_task) {
         write_unlock(&journal->j_state_lock);
         wake_up(&journal->j_wait_commit);
         wait_event(journal->j_wait_done_commit, journal->j_task == NULL);
         write_lock(&journal->j_state_lock);
     }
     write_unlock(&journal->j_state_lock);
 }
 
 /*
  * jbd2_journal_write_metadata_buffer: write a metadata buffer to the journal.
  *
  * Writes a metadata buffer to a given disk block.  The actual IO is not
  * performed but a new buffer_head is constructed which labels the data
  * to be written with the correct destination disk block.
  *
  * Any magic-number escaping which needs to be done will cause a
  * copy-out here.  If the buffer happens to start with the
  * JBD2_MAGIC_NUMBER, then we can't write it to the log directly: the
  * magic number is only written to the log for descripter blocks.  In
  * this case, we copy the data and replace the first word with 0, and we
  * return a result code which indicates that this buffer needs to be
  * marked as an escaped buffer in the corresponding log descriptor
  * block.  The missing word can then be restored when the block is read
  * during recovery.
  *
  * If the source buffer has already been modified by a new transaction
  * since we took the last commit snapshot, we use the frozen copy of
  * that data for IO. If we end up using the existing buffer_head's data
  * for the write, then we have to make sure nobody modifies it while the
  * IO is in progress. do_get_write_access() handles this.
  *
  * The function returns a pointer to the buffer_head to be used for IO.
  *
  *
  * Return value:
  *  <0: Error
  * >=0: Finished OK
  *
  * On success:
  * Bit 0 set == escape performed on the data
  * Bit 1 set == buffer copy-out performed (kfree the data after IO)
  */
 
 int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
                   struct journal_head  *jh_in,
                   struct buffer_head **bh_out,
                   sector_t blocknr)
 {
     int need_copy_out = 0;
     int done_copy_out = 0;
     int do_escape = 0;
     char *mapped_data;
     struct buffer_head *new_bh;
     struct page *new_page;
     unsigned int new_offset;
     struct buffer_head *bh_in = jh2bh(jh_in);
     journal_t *journal = transaction->t_journal;
 
     /*
      * The buffer really shouldn't be locked: only the current committing
      * transaction is allowed to write it, so nobody else is allowed
      * to do any IO.
      *
      * akpm: except if we're journalling data, and write() output is
      * also part of a shared mapping, and another thread has
      * decided to launch a writepage() against this buffer.
      */
     J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));
 
     new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
 
     /* keep subsequent assertions sane */
     atomic_set(&new_bh->b_count, 1);
 
     spin_lock(&jh_in->b_state_lock);
 repeat:
     /*
      * If a new transaction has already done a buffer copy-out, then
      * we use that version of the data for the commit.
      */
     if (jh_in->b_frozen_data) {
         done_copy_out = 1;
         new_page = virt_to_page(jh_in->b_frozen_data);
         new_offset = offset_in_page(jh_in->b_frozen_data);
     } else {
         new_page = jh2bh(jh_in)->b_page;
         new_offset = offset_in_page(jh2bh(jh_in)->b_data);
     }
 
     mapped_data = kmap_atomic(new_page);
     /*
      * Fire data frozen trigger if data already wasn't frozen.  Do this
      * before checking for escaping, as the trigger may modify the magic
      * offset.  If a copy-out happens afterwards, it will have the correct
      * data in the buffer.
      */
     if (!done_copy_out)
         jbd2_buffer_frozen_trigger(jh_in, mapped_data + new_offset,
                        jh_in->b_triggers);
 
     /*
      * Check for escaping
      */
     if (*((__be32 *)(mapped_data + new_offset)) ==
                 cpu_to_be32(JBD2_MAGIC_NUMBER)) {
         need_copy_out = 1;
         do_escape = 1;
     }
     kunmap_atomic(mapped_data);
 
     /*
      * Do we need to do a data copy?
      */
     if (need_copy_out && !done_copy_out) {
         char *tmp;
 
         spin_unlock(&jh_in->b_state_lock);
         tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
         if (!tmp) {
             brelse(new_bh);
             return -ENOMEM;
         }
         spin_lock(&jh_in->b_state_lock);
         if (jh_in->b_frozen_data) {
             jbd2_free(tmp, bh_in->b_size);
             goto repeat;
         }
 
         jh_in->b_frozen_data = tmp;
         mapped_data = kmap_atomic(new_page);
         memcpy(tmp, mapped_data + new_offset, bh_in->b_size);
         kunmap_atomic(mapped_data);
 
         new_page = virt_to_page(tmp);
         new_offset = offset_in_page(tmp);
         done_copy_out = 1;
 
         /*
          * This isn't strictly necessary, as we're using frozen
          * data for the escaping, but it keeps consistency with
          * b_frozen_data usage.
          */
         jh_in->b_frozen_triggers = jh_in->b_triggers;
     }
 
     /*
      * Did we need to do an escaping?  Now we've done all the
      * copying, we can finally do so.
      */
     if (do_escape) {
         mapped_data = kmap_atomic(new_page);
         *((unsigned int *)(mapped_data + new_offset)) = 0;
         kunmap_atomic(mapped_data);
     }
 
     set_bh_page(new_bh, new_page, new_offset);
     new_bh->b_size = bh_in->b_size;
     new_bh->b_bdev = journal->j_dev;
     new_bh->b_blocknr = blocknr;
     new_bh->b_private = bh_in;
     set_buffer_mapped(new_bh);
     set_buffer_dirty(new_bh);
 
     *bh_out = new_bh;
 
     /*
      * The to-be-written buffer needs to get moved to the io queue,
      * and the original buffer whose contents we are shadowing or
      * copying is moved to the transaction's shadow queue.
      */
     JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
     spin_lock(&journal->j_list_lock);
     __jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
     spin_unlock(&journal->j_list_lock);
     set_buffer_shadow(bh_in);
     spin_unlock(&jh_in->b_state_lock);
 
     return do_escape | (done_copy_out << 1);
 }
 
 /*
  * Allocation code for the journal file.  Manage the space left in the
  * journal, so that we can begin checkpointing when appropriate.
  */
 
 /*
  * Called with j_state_lock locked for writing.
  * Returns true if a transaction commit was started.
  */
 static int __jbd2_log_start_commit(journal_t *journal, tid_t target)
 {
     /* Return if the txn has already requested to be committed */
     if (journal->j_commit_request == target)
         return 0;
 
     /*
      * The only transaction we can possibly wait upon is the
      * currently running transaction (if it exists).  Otherwise,
      * the target tid must be an old one.
      */
     if (journal->j_running_transaction &&
         journal->j_running_transaction->t_tid == target) {
         /*
          * We want a new commit: OK, mark the request and wakeup the
          * commit thread.  We do _not_ do the commit ourselves.
          */
 
         journal->j_commit_request = target;
         jbd2_debug(1, "JBD2: requesting commit %u/%u\n",
               journal->j_commit_request,
               journal->j_commit_sequence);
         journal->j_running_transaction->t_requested = jiffies;
         wake_up(&journal->j_wait_commit);
         return 1;
     } else if (!tid_geq(journal->j_commit_request, target))
         /* This should never happen, but if it does, preserve
            the evidence before kjournald goes into a loop and
            increments j_commit_sequence beyond all recognition. */
         WARN_ONCE(1, "JBD2: bad log_start_commit: %u %u %u %u\n",
               journal->j_commit_request,
               journal->j_commit_sequence,
               target, journal->j_running_transaction ?
               journal->j_running_transaction->t_tid : 0);
     return 0;
 }
 
 int jbd2_log_start_commit(journal_t *journal, tid_t tid)
 {
     int ret;
 
     write_lock(&journal->j_state_lock);
     ret = __jbd2_log_start_commit(journal, tid);
     write_unlock(&journal->j_state_lock);
     return ret;
 }
 
 /*
  * Force and wait any uncommitted transactions.  We can only force the running
  * transaction if we don't have an active handle, otherwise, we will deadlock.
  * Returns: <0 in case of error,
  *           0 if nothing to commit,
  *           1 if transaction was successfully committed.
  */
 static int __jbd2_journal_force_commit(journal_t *journal)
 {
     transaction_t *transaction = NULL;
     tid_t tid;
     int need_to_start = 0, ret = 0;
 
     read_lock(&journal->j_state_lock);
     if (journal->j_running_transaction && !current->journal_info) {
         transaction = journal->j_running_transaction;
         if (!tid_geq(journal->j_commit_request, transaction->t_tid))
             need_to_start = 1;
     } else if (journal->j_committing_transaction)
         transaction = journal->j_committing_transaction;
 
     if (!transaction) {
         /* Nothing to commit */
         read_unlock(&journal->j_state_lock);
         return 0;
     }
     tid = transaction->t_tid;
     read_unlock(&journal->j_state_lock);
     if (need_to_start)
         jbd2_log_start_commit(journal, tid);
     ret = jbd2_log_wait_commit(journal, tid);
     if (!ret)
         ret = 1;
 
     return ret;
 }
 
 /**
  * jbd2_journal_force_commit_nested - Force and wait upon a commit if the
  * calling process is not within transaction.
  *
  * @journal: journal to force
  * Returns true if progress was made.
  *
  * This is used for forcing out undo-protected data which contains
  * bitmaps, when the fs is running out of space.
  */
 int jbd2_journal_force_commit_nested(journal_t *journal)
 {
     int ret;
 
     ret = __jbd2_journal_force_commit(journal);
     return ret > 0;
 }
 
 /**
  * jbd2_journal_force_commit() - force any uncommitted transactions
  * @journal: journal to force
  *
  * Caller want unconditional commit. We can only force the running transaction
  * if we don't have an active handle, otherwise, we will deadlock.
  */
 int jbd2_journal_force_commit(journal_t *journal)
 {
     int ret;
 
     J_ASSERT(!current->journal_info);
     ret = __jbd2_journal_force_commit(journal);
     if (ret > 0)
         ret = 0;
     return ret;
 }
 
 /*
  * Start a commit of the current running transaction (if any).  Returns true
  * if a transaction is going to be committed (or is currently already
  * committing), and fills its tid in at *ptid
  */
 int jbd2_journal_start_commit(journal_t *journal, tid_t *ptid)
 {
     int ret = 0;
 
     write_lock(&journal->j_state_lock);
     if (journal->j_running_transaction) {
         tid_t tid = journal->j_running_transaction->t_tid;
 
         __jbd2_log_start_commit(journal, tid);
         /* There's a running transaction and we've just made sure
          * it's commit has been scheduled. */
         if (ptid)
             *ptid = tid;
         ret = 1;
     } else if (journal->j_committing_transaction) {
         /*
          * If commit has been started, then we have to wait for
          * completion of that transaction.
          */
         if (ptid)
             *ptid = journal->j_committing_transaction->t_tid;
         ret = 1;
     }
     write_unlock(&journal->j_state_lock);
     return ret;
 }
 
 /*
  * Return 1 if a given transaction has not yet sent barrier request
  * connected with a transaction commit. If 0 is returned, transaction
  * may or may not have sent the barrier. Used to avoid sending barrier
  * twice in common cases.
  */
 int jbd2_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
 {
     int ret = 0;
     transaction_t *commit_trans;
 
     if (!(journal->j_flags & JBD2_BARRIER))
         return 0;
     read_lock(&journal->j_state_lock);
     /* Transaction already committed? */
     if (tid_geq(journal->j_commit_sequence, tid))
         goto out;
     commit_trans = journal->j_committing_transaction;
     if (!commit_trans || commit_trans->t_tid != tid) {
         ret = 1;
         goto out;
     }
     /*
      * Transaction is being committed and we already proceeded to
      * submitting a flush to fs partition?
      */
     if (journal->j_fs_dev != journal->j_dev) {
         if (!commit_trans->t_need_data_flush ||
             commit_trans->t_state >= T_COMMIT_DFLUSH)
             goto out;
     } else {
         if (commit_trans->t_state >= T_COMMIT_JFLUSH)
             goto out;
     }
     ret = 1;
 out:
     read_unlock(&journal->j_state_lock);
     return ret;
 }
 EXPORT_SYMBOL(jbd2_trans_will_send_data_barrier);
 
 /*
  * Wait for a specified commit to complete.
  * The caller may not hold the journal lock.
  */
 int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
 {
     int err = 0;
 
     read_lock(&journal->j_state_lock);
 #ifdef CONFIG_PROVE_LOCKING
     /*
      * Some callers make sure transaction is already committing and in that
      * case we cannot block on open handles anymore. So don't warn in that
      * case.
      */
     if (tid_gt(tid, journal->j_commit_sequence) &&
         (!journal->j_committing_transaction ||
          journal->j_committing_transaction->t_tid != tid)) {
         read_unlock(&journal->j_state_lock);
         jbd2_might_wait_for_commit(journal);
         read_lock(&journal->j_state_lock);
     }
 #endif
 #ifdef CONFIG_JBD2_DEBUG
     if (!tid_geq(journal->j_commit_request, tid)) {
         printk(KERN_ERR
                "%s: error: j_commit_request=%u, tid=%u\n",
                __func__, journal->j_commit_request, tid);
     }
 #endif
     while (tid_gt(tid, journal->j_commit_sequence)) {
         jbd2_debug(1, "JBD2: want %u, j_commit_sequence=%u\n",
                   tid, journal->j_commit_sequence);
         read_unlock(&journal->j_state_lock);
         wake_up(&journal->j_wait_commit);
         wait_event(journal->j_wait_done_commit,
                 !tid_gt(tid, journal->j_commit_sequence));
         read_lock(&journal->j_state_lock);
     }
     read_unlock(&journal->j_state_lock);
 
     if (unlikely(is_journal_aborted(journal)))
         err = -EIO;
     return err;
 }
 
 /*
  * Start a fast commit. If there's an ongoing fast or full commit wait for
  * it to complete. Returns 0 if a new fast commit was started. Returns -EALREADY
  * if a fast commit is not needed, either because there's an already a commit
  * going on or this tid has already been committed. Returns -EINVAL if no jbd2
  * commit has yet been performed.
  */
 int jbd2_fc_begin_commit(journal_t *journal, tid_t tid)
 {
     if (unlikely(is_journal_aborted(journal)))
         return -EIO;
     /*
      * Fast commits only allowed if at least one full commit has
      * been processed.
      */
     if (!journal->j_stats.ts_tid)
         return -EINVAL;
 
     write_lock(&journal->j_state_lock);
     if (tid <= journal->j_commit_sequence) {
         write_unlock(&journal->j_state_lock);
         return -EALREADY;
     }
 
     if (journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
         (journal->j_flags & JBD2_FAST_COMMIT_ONGOING)) {
         DEFINE_WAIT(wait);
 
         prepare_to_wait(&journal->j_fc_wait, &wait,
                 TASK_UNINTERRUPTIBLE);
         write_unlock(&journal->j_state_lock);
         schedule();
         finish_wait(&journal->j_fc_wait, &wait);
         return -EALREADY;
     }
     journal->j_flags |= JBD2_FAST_COMMIT_ONGOING;
     write_unlock(&journal->j_state_lock);
     jbd2_journal_lock_updates(journal);
 
     return 0;
 }
 EXPORT_SYMBOL(jbd2_fc_begin_commit);
 
 /*
  * Stop a fast commit. If fallback is set, this function starts commit of
  * TID tid before any other fast commit can start.
  */
 static int __jbd2_fc_end_commit(journal_t *journal, tid_t tid, bool fallback)
 {
     jbd2_journal_unlock_updates(journal);
     if (journal->j_fc_cleanup_callback)
         journal->j_fc_cleanup_callback(journal, 0, tid);
     write_lock(&journal->j_state_lock);
     journal->j_flags &= ~JBD2_FAST_COMMIT_ONGOING;
     if (fallback)
         journal->j_flags |= JBD2_FULL_COMMIT_ONGOING;
     write_unlock(&journal->j_state_lock);
     wake_up(&journal->j_fc_wait);
     if (fallback)
         return jbd2_complete_transaction(journal, tid);
     return 0;
 }
 
 int jbd2_fc_end_commit(journal_t *journal)
 {
     return __jbd2_fc_end_commit(journal, 0, false);
 }
 EXPORT_SYMBOL(jbd2_fc_end_commit);
 
 int jbd2_fc_end_commit_fallback(journal_t *journal)
 {
     tid_t tid;
 
     read_lock(&journal->j_state_lock);
     tid = journal->j_running_transaction ?
         journal->j_running_transaction->t_tid : 0;
     read_unlock(&journal->j_state_lock);
     return __jbd2_fc_end_commit(journal, tid, true);
 }
 EXPORT_SYMBOL(jbd2_fc_end_commit_fallback);
 
 /* Return 1 when transaction with given tid has already committed. */
 int jbd2_transaction_committed(journal_t *journal, tid_t tid)
 {
     int ret = 1;
 
     read_lock(&journal->j_state_lock);
     if (journal->j_running_transaction &&
         journal->j_running_transaction->t_tid == tid)
         ret = 0;
     if (journal->j_committing_transaction &&
         journal->j_committing_transaction->t_tid == tid)
         ret = 0;
     read_unlock(&journal->j_state_lock);
     return ret;
 }
 EXPORT_SYMBOL(jbd2_transaction_committed);
 
 /*
  * When this function returns the transaction corresponding to tid
  * will be completed.  If the transaction has currently running, start
  * committing that transaction before waiting for it to complete.  If
  * the transaction id is stale, it is by definition already completed,
  * so just return SUCCESS.
  */
 int jbd2_complete_transaction(journal_t *journal, tid_t tid)
 {
     int need_to_wait = 1;
 
     read_lock(&journal->j_state_lock);
     if (journal->j_running_transaction &&
         journal->j_running_transaction->t_tid == tid) {
         if (journal->j_commit_request != tid) {
             /* transaction not yet started, so request it */
             read_unlock(&journal->j_state_lock);
             jbd2_log_start_commit(journal, tid);
             goto wait_commit;
         }
     } else if (!(journal->j_committing_transaction &&
              journal->j_committing_transaction->t_tid == tid))
         need_to_wait = 0;
     read_unlock(&journal->j_state_lock);
     if (!need_to_wait)
         return 0;
 wait_commit:
     return jbd2_log_wait_commit(journal, tid);
 }
 EXPORT_SYMBOL(jbd2_complete_transaction);
 
 /*
  * Log buffer allocation routines:
  */
 
 int jbd2_journal_next_log_block(journal_t *journal, unsigned long long *retp)
 {
     unsigned long blocknr;
 
     write_lock(&journal->j_state_lock);
     J_ASSERT(journal->j_free > 1);
 
     blocknr = journal->j_head;
     journal->j_head++;
     journal->j_free--;
     if (journal->j_head == journal->j_last)
         journal->j_head = journal->j_first;
     write_unlock(&journal->j_state_lock);
     return jbd2_journal_bmap(journal, blocknr, retp);
 }
 
 /* Map one fast commit buffer for use by the file system */
 int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
 {
     unsigned long long pblock;
     unsigned long blocknr;
     int ret = 0;
     struct buffer_head *bh;
     int fc_off;
 
     *bh_out = NULL;
 
     if (journal->j_fc_off + journal->j_fc_first < journal->j_fc_last) {
         fc_off = journal->j_fc_off;
         blocknr = journal->j_fc_first + fc_off;
         journal->j_fc_off++;
     } else {
         ret = -EINVAL;
     }
 
     if (ret)
         return ret;
 
     ret = jbd2_journal_bmap(journal, blocknr, &pblock);
     if (ret)
         return ret;
 
     bh = __getblk(journal->j_dev, pblock, journal->j_blocksize);
     if (!bh)
         return -ENOMEM;
 
 
     journal->j_fc_wbuf[fc_off] = bh;
 
     *bh_out = bh;
 
     return 0;
 }
 EXPORT_SYMBOL(jbd2_fc_get_buf);
 
 /*
  * Wait on fast commit buffers that were allocated by jbd2_fc_get_buf
  * for completion.
  */
 int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
 {
     struct buffer_head *bh;
     int i, j_fc_off;
 
     j_fc_off = journal->j_fc_off;
 
     /*
      * Wait in reverse order to minimize chances of us being woken up before
      * all IOs have completed
      */
     for (i = j_fc_off - 1; i >= j_fc_off - num_blks; i--) {
         bh = journal->j_fc_wbuf[i];
         wait_on_buffer(bh);
         put_bh(bh);
         journal->j_fc_wbuf[i] = NULL;
         if (unlikely(!buffer_uptodate(bh)))
             return -EIO;
     }
 
     return 0;
 }
 EXPORT_SYMBOL(jbd2_fc_wait_bufs);
 
 int jbd2_fc_release_bufs(journal_t *journal)
 {
     struct buffer_head *bh;
     int i, j_fc_off;
 
     j_fc_off = journal->j_fc_off;
 
     for (i = j_fc_off - 1; i >= 0; i--) {
         bh = journal->j_fc_wbuf[i];
         if (!bh)
             break;
         put_bh(bh);
         journal->j_fc_wbuf[i] = NULL;
     }
 
     return 0;
 }
 EXPORT_SYMBOL(jbd2_fc_release_bufs);
 
 /*
  * Conversion of logical to physical block numbers for the journal
  *
  * On external journals the journal blocks are identity-mapped, so
  * this is a no-op.  If needed, we can use j_blk_offset - everything is
  * ready.
  */
 int jbd2_journal_bmap(journal_t *journal, unsigned long blocknr,
          unsigned long long *retp)
 {
     int err = 0;
     unsigned long long ret;
     sector_t block = 0;
 
     if (journal->j_inode) {
         block = blocknr;
         ret = bmap(journal->j_inode, &block);
 
         if (ret || !block) {
             printk(KERN_ALERT "%s: journal block not found "
                     "at offset %lu on %s\n",
                    __func__, blocknr, journal->j_devname);
             err = -EIO;
             jbd2_journal_abort(journal, err);
         } else {
             *retp = block;
         }
 
     } else {
         *retp = blocknr; /* +journal->j_blk_offset */
     }
     return err;
 }
 
 /*
  * We play buffer_head aliasing tricks to write data/metadata blocks to
  * the journal without copying their contents, but for journal
  * descriptor blocks we do need to generate bona fide buffers.
  *
  * After the caller of jbd2_journal_get_descriptor_buffer() has finished modifying
  * the buffer's contents they really should run flush_dcache_page(bh->b_page).
  * But we don't bother doing that, so there will be coherency problems with
  * mmaps of blockdevs which hold live JBD-controlled filesystems.
  */
 struct buffer_head *
 jbd2_journal_get_descriptor_buffer(transaction_t *transaction, int type)
 {
     journal_t *journal = transaction->t_journal;
     struct buffer_head *bh;
     unsigned long long blocknr;
     journal_header_t *header;
     int err;
 
     err = jbd2_journal_next_log_block(journal, &blocknr);
 
     if (err)
         return NULL;
 
     bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
     if (!bh)
         return NULL;
     atomic_dec(&transaction->t_outstanding_credits);
     lock_buffer(bh);
     memset(bh->b_data, 0, journal->j_blocksize);
     header = (journal_header_t *)bh->b_data;
     header->h_magic = cpu_to_be32(JBD2_MAGIC_NUMBER);
     header->h_blocktype = cpu_to_be32(type);
     header->h_sequence = cpu_to_be32(transaction->t_tid);
     set_buffer_uptodate(bh);
     unlock_buffer(bh);
     BUFFER_TRACE(bh, "return this buffer");
     return bh;
 }
 
 void jbd2_descriptor_block_csum_set(journal_t *j, struct buffer_head *bh)
 {
     struct jbd2_journal_block_tail *tail;
     __u32 csum;
 
     if (!jbd2_journal_has_csum_v2or3(j))
         return;
 
     tail = (struct jbd2_journal_block_tail *)(bh->b_data + j->j_blocksize -
             sizeof(struct jbd2_journal_block_tail));
     tail->t_checksum = 0;
     csum = jbd2_chksum(j, j->j_csum_seed, bh->b_data, j->j_blocksize);
     tail->t_checksum = cpu_to_be32(csum);
 }
 
 /*
  * Return tid of the oldest transaction in the journal and block in the journal
  * where the transaction starts.
  *
  * If the journal is now empty, return which will be the next transaction ID
  * we will write and where will that transaction start.
  *
  * The return value is 0 if journal tail cannot be pushed any further, 1 if
  * it can.
  */
 int jbd2_journal_get_log_tail(journal_t *journal, tid_t *tid,
                   unsigned long *block)
 {
     transaction_t *transaction;
     int ret;
 
     read_lock(&journal->j_state_lock);
     spin_lock(&journal->j_list_lock);
     transaction = journal->j_checkpoint_transactions;
     if (transaction) {
         *tid = transaction->t_tid;
         *block = transaction->t_log_start;
     } else if ((transaction = journal->j_committing_transaction) != NULL) {
         *tid = transaction->t_tid;
         *block = transaction->t_log_start;
     } else if ((transaction = journal->j_running_transaction) != NULL) {
         *tid = transaction->t_tid;
         *block = journal->j_head;
     } else {
         *tid = journal->j_transaction_sequence;
         *block = journal->j_head;
     }
     ret = tid_gt(*tid, journal->j_tail_sequence);
     spin_unlock(&journal->j_list_lock);
     read_unlock(&journal->j_state_lock);
 
     return ret;
 }
 
 /*
  * Update information in journal structure and in on disk journal superblock
  * about log tail. This function does not check whether information passed in
  * really pushes log tail further. It's responsibility of the caller to make
  * sure provided log tail information is valid (e.g. by holding
  * j_checkpoint_mutex all the time between computing log tail and calling this
  * function as is the case with jbd2_cleanup_journal_tail()).
  *
  * Requires j_checkpoint_mutex
  */
 int __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block)
 {
     unsigned long freed;
     int ret;
 
     BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
 
     /*
      * We cannot afford for write to remain in drive's caches since as
      * soon as we update j_tail, next transaction can start reusing journal
      * space and if we lose sb update during power failure we'd replay
      * old transaction with possibly newly overwritten data.
      */
     ret = jbd2_journal_update_sb_log_tail(journal, tid, block,
                           REQ_SYNC | REQ_FUA);
     if (ret)
         goto out;
 
     write_lock(&journal->j_state_lock);
     freed = block - journal->j_tail;
     if (block < journal->j_tail)
         freed += journal->j_last - journal->j_first;
 
     trace_jbd2_update_log_tail(journal, tid, block, freed);
     jbd2_debug(1,
           "Cleaning journal tail from %u to %u (offset %lu), "
           "freeing %lu\n",
           journal->j_tail_sequence, tid, block, freed);
 
     journal->j_free += freed;
     journal->j_tail_sequence = tid;
     journal->j_tail = block;
     write_unlock(&journal->j_state_lock);
 
 out:
     return ret;
 }
 
 /*
  * This is a variation of __jbd2_update_log_tail which checks for validity of
  * provided log tail and locks j_checkpoint_mutex. So it is safe against races
  * with other threads updating log tail.
  */
 void jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block)
 {
     mutex_lock_io(&journal->j_checkpoint_mutex);
     if (tid_gt(tid, journal->j_tail_sequence))
         __jbd2_update_log_tail(journal, tid, block);
     mutex_unlock(&journal->j_checkpoint_mutex);
 }
 
 struct jbd2_stats_proc_session {
     journal_t *journal;
     struct transaction_stats_s *stats;
     int start;
     int max;
 };
 
 static void *jbd2_seq_info_start(struct seq_file *seq, loff_t *pos)
 {
     return *pos ? NULL : SEQ_START_TOKEN;
 }
 
 static void *jbd2_seq_info_next(struct seq_file *seq, void *v, loff_t *pos)
 {
     (*pos)++;
     return NULL;
 }
 
 static int jbd2_seq_info_show(struct seq_file *seq, void *v)
 {
     struct jbd2_stats_proc_session *s = seq->private;
 
     if (v != SEQ_START_TOKEN)
         return 0;
     seq_printf(seq, "%lu transactions (%lu requested), "
            "each up to %u blocks\n",
            s->stats->ts_tid, s->stats->ts_requested,
            s->journal->j_max_transaction_buffers);
     if (s->stats->ts_tid == 0)
         return 0;
     seq_printf(seq, "average: \n  %ums waiting for transaction\n",
         jiffies_to_msecs(s->stats->run.rs_wait / s->stats->ts_tid));
     seq_printf(seq, "  %ums request delay\n",
         (s->stats->ts_requested == 0) ? 0 :
         jiffies_to_msecs(s->stats->run.rs_request_delay /
                  s->stats->ts_requested));
     seq_printf(seq, "  %ums running transaction\n",
         jiffies_to_msecs(s->stats->run.rs_running / s->stats->ts_tid));
     seq_printf(seq, "  %ums transaction was being locked\n",
         jiffies_to_msecs(s->stats->run.rs_locked / s->stats->ts_tid));
     seq_printf(seq, "  %ums flushing data (in ordered mode)\n",
         jiffies_to_msecs(s->stats->run.rs_flushing / s->stats->ts_tid));
     seq_printf(seq, "  %ums logging transaction\n",
         jiffies_to_msecs(s->stats->run.rs_logging / s->stats->ts_tid));
     seq_printf(seq, "  %lluus average transaction commit time\n",
            div_u64(s->journal->j_average_commit_time, 1000));
     seq_printf(seq, "  %lu handles per transaction\n",
         s->stats->run.rs_handle_count / s->stats->ts_tid);
     seq_printf(seq, "  %lu blocks per transaction\n",
         s->stats->run.rs_blocks / s->stats->ts_tid);
     seq_printf(seq, "  %lu logged blocks per transaction\n",
         s->stats->run.rs_blocks_logged / s->stats->ts_tid);
     return 0;
 }
 
 static void jbd2_seq_info_stop(struct seq_file *seq, void *v)
 {
 }
 
 static const struct seq_operations jbd2_seq_info_ops = {
     .start  = jbd2_seq_info_start,
     .next   = jbd2_seq_info_next,
     .stop   = jbd2_seq_info_stop,
     .show   = jbd2_seq_info_show,
 };
 
 static int jbd2_seq_info_open(struct inode *inode, struct file *file)
 {
     journal_t *journal = pde_data(inode);
     struct jbd2_stats_proc_session *s;
     int rc, size;
 
     s = kmalloc(sizeof(*s), GFP_KERNEL);
     if (s == NULL)
         return -ENOMEM;
     size = sizeof(struct transaction_stats_s);
     s->stats = kmalloc(size, GFP_KERNEL);
     if (s->stats == NULL) {
         kfree(s);
         return -ENOMEM;
     }
     spin_lock(&journal->j_history_lock);
     memcpy(s->stats, &journal->j_stats, size);
     s->journal = journal;
     spin_unlock(&journal->j_history_lock);
 
     rc = seq_open(file, &jbd2_seq_info_ops);
     if (rc == 0) {
         struct seq_file *m = file->private_data;
         m->private = s;
     } else {
         kfree(s->stats);
         kfree(s);
     }
     return rc;
 
 }
 
 static int jbd2_seq_info_release(struct inode *inode, struct file *file)
 {
     struct seq_file *seq = file->private_data;
     struct jbd2_stats_proc_session *s = seq->private;
     kfree(s->stats);
     kfree(s);
     return seq_release(inode, file);
 }
 
 static const struct proc_ops jbd2_info_proc_ops = {
     .proc_open  = jbd2_seq_info_open,
     .proc_read  = seq_read,
     .proc_lseek = seq_lseek,
     .proc_release   = jbd2_seq_info_release,
 };
 
 static struct proc_dir_entry *proc_jbd2_stats;
 
 static void jbd2_stats_proc_init(journal_t *journal)
 {
     journal->j_proc_entry = proc_mkdir(journal->j_devname, proc_jbd2_stats);
     if (journal->j_proc_entry) {
         proc_create_data("info", S_IRUGO, journal->j_proc_entry,
                  &jbd2_info_proc_ops, journal);
     }
 }
 
 static void jbd2_stats_proc_exit(journal_t *journal)
 {
     remove_proc_entry("info", journal->j_proc_entry);
     remove_proc_entry(journal->j_devname, proc_jbd2_stats);
 }
 
 /* Minimum size of descriptor tag */
 static int jbd2_min_tag_size(void)
 {
     /*
      * Tag with 32-bit block numbers does not use last four bytes of the
      * structure
      */
     return sizeof(journal_block_tag_t) - 4;
 }
 
 /**
  * jbd2_journal_shrink_scan()
  * @shrink: shrinker to work on
  * @sc: reclaim request to process
  *
  * Scan the checkpointed buffer on the checkpoint list and release the
  * journal_head.
  */
 static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
                           struct shrink_control *sc)
 {
     journal_t *journal = container_of(shrink, journal_t, j_shrinker);
     unsigned long nr_to_scan = sc->nr_to_scan;
     unsigned long nr_shrunk;
     unsigned long count;
 
     count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
     trace_jbd2_shrink_scan_enter(journal, sc->nr_to_scan, count);
 
     nr_shrunk = jbd2_journal_shrink_checkpoint_list(journal, &nr_to_scan);
 
     count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
     trace_jbd2_shrink_scan_exit(journal, nr_to_scan, nr_shrunk, count);
 
     return nr_shrunk;
 }
 
 /**
  * jbd2_journal_shrink_count()
  * @shrink: shrinker to work on
  * @sc: reclaim request to process
  *
  * Count the number of checkpoint buffers on the checkpoint list.
  */
 static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
                            struct shrink_control *sc)
 {
     journal_t *journal = container_of(shrink, journal_t, j_shrinker);
     unsigned long count;
 
     count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
     trace_jbd2_shrink_count(journal, sc->nr_to_scan, count);
 
     return count;
 }
 
 /*
  * Management for journal control blocks: functions to create and
  * destroy journal_t structures, and to initialise and read existing
  * journal blocks from disk.  */
 
 /* First: create and setup a journal_t object in memory.  We initialise
  * very few fields yet: that has to wait until we have created the
  * journal structures from from scratch, or loaded them from disk. */
 
 static journal_t *journal_init_common(struct block_device *bdev,
             struct block_device *fs_dev,
             unsigned long long start, int len, int blocksize)
 {
     static struct lock_class_key jbd2_trans_commit_key;
     journal_t *journal;
     int err;
     struct buffer_head *bh;
     int n;
 
     journal = kzalloc(sizeof(*journal), GFP_KERNEL);
     if (!journal)
         return NULL;
 
     init_waitqueue_head(&journal->j_wait_transaction_locked);
     init_waitqueue_head(&journal->j_wait_done_commit);
     init_waitqueue_head(&journal->j_wait_commit);
     init_waitqueue_head(&journal->j_wait_updates);
     init_waitqueue_head(&journal->j_wait_reserved);
     init_waitqueue_head(&journal->j_fc_wait);
     mutex_init(&journal->j_abort_mutex);
     mutex_init(&journal->j_barrier);
     mutex_init(&journal->j_checkpoint_mutex);
     spin_lock_init(&journal->j_revoke_lock);
     spin_lock_init(&journal->j_list_lock);
     rwlock_init(&journal->j_state_lock);
 
     journal->j_commit_interval = (HZ * JBD2_DEFAULT_MAX_COMMIT_AGE);
     journal->j_min_batch_time = 0;
     journal->j_max_batch_time = 15000; /* 15ms */
     atomic_set(&journal->j_reserved_credits, 0);
 
     /* The journal is marked for error until we succeed with recovery! */
     journal->j_flags = JBD2_ABORT;
 
     /* Set up a default-sized revoke table for the new mount. */
     err = jbd2_journal_init_revoke(journal, JOURNAL_REVOKE_DEFAULT_HASH);
     if (err)
         goto err_cleanup;
 
     spin_lock_init(&journal->j_history_lock);
 
     lockdep_init_map(&journal->j_trans_commit_map, "jbd2_handle",
              &jbd2_trans_commit_key, 0);
 
     /* journal descriptor can store up to n blocks -bzzz */
     journal->j_blocksize = blocksize;
     journal->j_dev = bdev;
     journal->j_fs_dev = fs_dev;
     journal->j_blk_offset = start;
     journal->j_total_len = len;
     /* We need enough buffers to write out full descriptor block. */
     n = journal->j_blocksize / jbd2_min_tag_size();
     journal->j_wbufsize = n;
     journal->j_fc_wbuf = NULL;
     journal->j_wbuf = kmalloc_array(n, sizeof(struct buffer_head *),
                     GFP_KERNEL);
     if (!journal->j_wbuf)
         goto err_cleanup;
 
     bh = getblk_unmovable(journal->j_dev, start, journal->j_blocksize);
     if (!bh) {
         pr_err("%s: Cannot get buffer for journal superblock\n",
             __func__);
         goto err_cleanup;
     }
     journal->j_sb_buffer = bh;
     journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
     journal->j_shrink_transaction = NULL;
     journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
     journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
     journal->j_shrinker.seeks = DEFAULT_SEEKS;
     journal->j_shrinker.batch = journal->j_max_transaction_buffers;
 
     if (percpu_counter_init(&journal->j_checkpoint_jh_count, 0, GFP_KERNEL))
         goto err_cleanup;
 
     if (register_shrinker(&journal->j_shrinker, "jbd2-journal:(%u:%u)",
                   MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev))) {
         percpu_counter_destroy(&journal->j_checkpoint_jh_count);
         goto err_cleanup;
     }
     return journal;
 
 err_cleanup:
     brelse(journal->j_sb_buffer);
     kfree(journal->j_wbuf);
     jbd2_journal_destroy_revoke(journal);
     kfree(journal);
     return NULL;
 }
 
 /* jbd2_journal_init_dev and jbd2_journal_init_inode:
  *
  * Create a journal structure assigned some fixed set of disk blocks to
  * the journal.  We don't actually touch those disk blocks yet, but we
  * need to set up all of the mapping information to tell the journaling
  * system where the journal blocks are.
  *
  */
 
 /**
  *  journal_t * jbd2_journal_init_dev() - creates and initialises a journal structure
  *  @bdev: Block device on which to create the journal
  *  @fs_dev: Device which hold journalled filesystem for this journal.
  *  @start: Block nr Start of journal.
  *  @len:  Length of the journal in blocks.
  *  @blocksize: blocksize of journalling device
  *
  *  Returns: a newly created journal_t *
  *
  *  jbd2_journal_init_dev creates a journal which maps a fixed contiguous
  *  range of blocks on an arbitrary block device.
  *
  */
 journal_t *jbd2_journal_init_dev(struct block_device *bdev,
             struct block_device *fs_dev,
             unsigned long long start, int len, int blocksize)
 {
     journal_t *journal;
 
     journal = journal_init_common(bdev, fs_dev, start, len, blocksize);
     if (!journal)
         return NULL;
 
     snprintf(journal->j_devname, sizeof(journal->j_devname),
          "%pg", journal->j_dev);
     strreplace(journal->j_devname, '/', '!');
     jbd2_stats_proc_init(journal);
 
     return journal;
 }
 
 /**
  *  journal_t * jbd2_journal_init_inode () - creates a journal which maps to a inode.
  *  @inode: An inode to create the journal in
  *
  * jbd2_journal_init_inode creates a journal which maps an on-disk inode as
  * the journal.  The inode must exist already, must support bmap() and
  * must have all data blocks preallocated.
  */
 journal_t *jbd2_journal_init_inode(struct inode *inode)
 {
     journal_t *journal;
     sector_t blocknr;
     char *p;
     int err = 0;
 
     blocknr = 0;
     err = bmap(inode, &blocknr);
 
     if (err || !blocknr) {
         pr_err("%s: Cannot locate journal superblock\n",
             __func__);
         return NULL;
     }
 
     jbd2_debug(1, "JBD2: inode %s/%ld, size %lld, bits %d, blksize %ld\n",
           inode->i_sb->s_id, inode->i_ino, (long long) inode->i_size,
           inode->i_sb->s_blocksize_bits, inode->i_sb->s_blocksize);
 
     journal = journal_init_common(inode->i_sb->s_bdev, inode->i_sb->s_bdev,
             blocknr, inode->i_size >> inode->i_sb->s_blocksize_bits,
             inode->i_sb->s_blocksize);
     if (!journal)
         return NULL;
 
     journal->j_inode = inode;
     snprintf(journal->j_devname, sizeof(journal->j_devname),
          "%pg", journal->j_dev);
     p = strreplace(journal->j_devname, '/', '!');
     sprintf(p, "-%lu", journal->j_inode->i_ino);
     jbd2_stats_proc_init(journal);
 
     return journal;
 }
 
 /*
  * If the journal init or create aborts, we need to mark the journal
  * superblock as being NULL to prevent the journal destroy from writing
  * back a bogus superblock.
  */
 static void journal_fail_superblock(journal_t *journal)
 {
     struct buffer_head *bh = journal->j_sb_buffer;
     brelse(bh);
     journal->j_sb_buffer = NULL;
 }
 
 /*
  * Given a journal_t structure, initialise the various fields for
  * startup of a new journaling session.  We use this both when creating
  * a journal, and after recovering an old journal to reset it for
  * subsequent use.
  */
 
 static int journal_reset(journal_t *journal)
 {
     journal_superblock_t *sb = journal->j_superblock;
     unsigned long long first, last;
 
     first = be32_to_cpu(sb->s_first);
     last = be32_to_cpu(sb->s_maxlen);
     if (first + JBD2_MIN_JOURNAL_BLOCKS > last + 1) {
         printk(KERN_ERR "JBD2: Journal too short (blocks %llu-%llu).\n",
                first, last);
         journal_fail_superblock(journal);
         return -EINVAL;
     }
 
     journal->j_first = first;
     journal->j_last = last;
 
     journal->j_head = journal->j_first;
     journal->j_tail = journal->j_first;
     journal->j_free = journal->j_last - journal->j_first;
 
     journal->j_tail_sequence = journal->j_transaction_sequence;
     journal->j_commit_sequence = journal->j_transaction_sequence - 1;
     journal->j_commit_request = journal->j_commit_sequence;
 
     journal->j_max_transaction_buffers = jbd2_journal_get_max_txn_bufs(journal);
 
     /*
      * Now that journal recovery is done, turn fast commits off here. This
      * way, if fast commit was enabled before the crash but if now FS has
      * disabled it, we don't enable fast commits.
      */
     jbd2_clear_feature_fast_commit(journal);
 
     /*
      * As a special case, if the on-disk copy is already marked as needing
      * no recovery (s_start == 0), then we can safely defer the superblock
      * update until the next commit by setting JBD2_FLUSHED.  This avoids
      * attempting a write to a potential-readonly device.
      */
     if (sb->s_start == 0) {
         jbd2_debug(1, "JBD2: Skipping superblock update on recovered sb "
             "(start %ld, seq %u, errno %d)\n",
             journal->j_tail, journal->j_tail_sequence,
             journal->j_errno);
         journal->j_flags |= JBD2_FLUSHED;
     } else {
         /* Lock here to make assertions happy... */
         mutex_lock_io(&journal->j_checkpoint_mutex);
         /*
          * Update log tail information. We use REQ_FUA since new
          * transaction will start reusing journal space and so we
          * must make sure information about current log tail is on
          * disk before that.
          */
         jbd2_journal_update_sb_log_tail(journal,
                         journal->j_tail_sequence,
                         journal->j_tail,
                         REQ_SYNC | REQ_FUA);
         mutex_unlock(&journal->j_checkpoint_mutex);
     }
     return jbd2_journal_start_thread(journal);
 }
 
 /*
  * This function expects that the caller will have locked the journal
  * buffer head, and will return with it unlocked
  */
 static int jbd2_write_superblock(journal_t *journal, blk_opf_t write_flags)
 {
     struct buffer_head *bh = journal->j_sb_buffer;
     journal_superblock_t *sb = journal->j_superblock;
     int ret;
 
     /* Buffer got discarded which means block device got invalidated */
     if (!buffer_mapped(bh)) {
         unlock_buffer(bh);
         return -EIO;
     }
 
     trace_jbd2_write_superblock(journal, write_flags);
     if (!(journal->j_flags & JBD2_BARRIER))
         write_flags &= ~(REQ_FUA | REQ_PREFLUSH);
     if (buffer_write_io_error(bh)) {
         /*
          * Oh, dear.  A previous attempt to write the journal
          * superblock failed.  This could happen because the
          * USB device was yanked out.  Or it could happen to
          * be a transient write error and maybe the block will
          * be remapped.  Nothing we can do but to retry the
          * write and hope for the best.
          */
         printk(KERN_ERR "JBD2: previous I/O error detected "
                "for journal superblock update for %s.\n",
                journal->j_devname);
         clear_buffer_write_io_error(bh);
         set_buffer_uptodate(bh);
     }
     if (jbd2_journal_has_csum_v2or3(journal))
         sb->s_checksum = jbd2_superblock_csum(journal, sb);
     get_bh(bh);
     bh->b_end_io = end_buffer_write_sync;
     ret = submit_bh(REQ_OP_WRITE | write_flags, bh);
     wait_on_buffer(bh);
     if (buffer_write_io_error(bh)) {
         clear_buffer_write_io_error(bh);
         set_buffer_uptodate(bh);
         ret = -EIO;
     }
     if (ret) {
         printk(KERN_ERR "JBD2: Error %d detected when updating "
                "journal superblock for %s.\n", ret,
                journal->j_devname);
         if (!is_journal_aborted(journal))
             jbd2_journal_abort(journal, ret);
     }
 
     return ret;
 }
 
 /**
  * jbd2_journal_update_sb_log_tail() - Update log tail in journal sb on disk.
  * @journal: The journal to update.
  * @tail_tid: TID of the new transaction at the tail of the log
  * @tail_block: The first block of the transaction at the tail of the log
  * @write_flags: Flags for the journal sb write operation
  *
  * Update a journal's superblock information about log tail and write it to
  * disk, waiting for the IO to complete.
  */
 int jbd2_journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
                     unsigned long tail_block,
                     blk_opf_t write_flags)
 {
     journal_superblock_t *sb = journal->j_superblock;
     int ret;
 
     if (is_journal_aborted(journal))
         return -EIO;
     if (test_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags)) {
         jbd2_journal_abort(journal, -EIO);
         return -EIO;
     }
 
     BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
     jbd2_debug(1, "JBD2: updating superblock (start %lu, seq %u)\n",
           tail_block, tail_tid);
 
     lock_buffer(journal->j_sb_buffer);
     sb->s_sequence = cpu_to_be32(tail_tid);
     sb->s_start    = cpu_to_be32(tail_block);
 
     ret = jbd2_write_superblock(journal, write_flags);
     if (ret)
         goto out;
 
     /* Log is no longer empty */
     write_lock(&journal->j_state_lock);
     WARN_ON(!sb->s_sequence);
     journal->j_flags &= ~JBD2_FLUSHED;
     write_unlock(&journal->j_state_lock);
 
 out:
     return ret;
 }
 
 /**
  * jbd2_mark_journal_empty() - Mark on disk journal as empty.
  * @journal: The journal to update.
  * @write_flags: Flags for the journal sb write operation
  *
  * Update a journal's dynamic superblock fields to show that journal is empty.
  * Write updated superblock to disk waiting for IO to complete.
  */
 static void jbd2_mark_journal_empty(journal_t *journal, blk_opf_t write_flags)
 {
     journal_superblock_t *sb = journal->j_superblock;
     bool had_fast_commit = false;
 
     BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
     lock_buffer(journal->j_sb_buffer);
     if (sb->s_start == 0) {     /* Is it already empty? */
         unlock_buffer(journal->j_sb_buffer);
         return;
     }
 
     jbd2_debug(1, "JBD2: Marking journal as empty (seq %u)\n",
           journal->j_tail_sequence);
 
     sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
     sb->s_start    = cpu_to_be32(0);
     if (jbd2_has_feature_fast_commit(journal)) {
         /*
          * When journal is clean, no need to commit fast commit flag and
          * make file system incompatible with older kernels.
          */
         jbd2_clear_feature_fast_commit(journal);
         had_fast_commit = true;
     }
 
     jbd2_write_superblock(journal, write_flags);
 
     if (had_fast_commit)
         jbd2_set_feature_fast_commit(journal);
 
     /* Log is no longer empty */
     write_lock(&journal->j_state_lock);
     journal->j_flags |= JBD2_FLUSHED;
     write_unlock(&journal->j_state_lock);
 }
 
 /**
  * __jbd2_journal_erase() - Discard or zeroout journal blocks (excluding superblock)
  * @journal: The journal to erase.
  * @flags: A discard/zeroout request is sent for each physically contigous
  *  region of the journal. Either JBD2_JOURNAL_FLUSH_DISCARD or
  *  JBD2_JOURNAL_FLUSH_ZEROOUT must be set to determine which operation
  *  to perform.
  *
  * Note: JBD2_JOURNAL_FLUSH_ZEROOUT attempts to use hardware offload. Zeroes
  * will be explicitly written if no hardware offload is available, see
  * blkdev_issue_zeroout for more details.
  */
 static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
 {
     int err = 0;
     unsigned long block, log_offset; /* logical */
     unsigned long long phys_block, block_start, block_stop; /* physical */
     loff_t byte_start, byte_stop, byte_count;
 
     /* flags must be set to either discard or zeroout */
     if ((flags & ~JBD2_JOURNAL_FLUSH_VALID) || !flags ||
             ((flags & JBD2_JOURNAL_FLUSH_DISCARD) &&
             (flags & JBD2_JOURNAL_FLUSH_ZEROOUT)))
         return -EINVAL;
 
     if ((flags & JBD2_JOURNAL_FLUSH_DISCARD) &&
         !bdev_max_discard_sectors(journal->j_dev))
         return -EOPNOTSUPP;
 
     /*
      * lookup block mapping and issue discard/zeroout for each
      * contiguous region
      */
     log_offset = be32_to_cpu(journal->j_superblock->s_first);
     block_start =  ~0ULL;
     for (block = log_offset; block < journal->j_total_len; block++) {
         err = jbd2_journal_bmap(journal, block, &phys_block);
         if (err) {
             pr_err("JBD2: bad block at offset %lu", block);
             return err;
         }
 
         if (block_start == ~0ULL) {
             block_start = phys_block;
             block_stop = block_start - 1;
         }
 
         /*
          * last block not contiguous with current block,
          * process last contiguous region and return to this block on
          * next loop
          */
         if (phys_block != block_stop + 1) {
             block--;
         } else {
             block_stop++;
             /*
              * if this isn't the last block of journal,
              * no need to process now because next block may also
              * be part of this contiguous region
              */
             if (block != journal->j_total_len - 1)
                 continue;
         }
 
         /*
          * end of contiguous region or this is last block of journal,
          * take care of the region
          */
         byte_start = block_start * journal->j_blocksize;
         byte_stop = block_stop * journal->j_blocksize;
         byte_count = (block_stop - block_start + 1) *
                 journal->j_blocksize;
 
         truncate_inode_pages_range(journal->j_dev->bd_inode->i_mapping,
                 byte_start, byte_stop);
 
         if (flags & JBD2_JOURNAL_FLUSH_DISCARD) {
             err = blkdev_issue_discard(journal->j_dev,
                     byte_start >> SECTOR_SHIFT,
                     byte_count >> SECTOR_SHIFT,
                     GFP_NOFS);
         } else if (flags & JBD2_JOURNAL_FLUSH_ZEROOUT) {
             err = blkdev_issue_zeroout(journal->j_dev,
                     byte_start >> SECTOR_SHIFT,
                     byte_count >> SECTOR_SHIFT,
                     GFP_NOFS, 0);
         }
 
         if (unlikely(err != 0)) {
             pr_err("JBD2: (error %d) unable to wipe journal at physical blocks %llu - %llu",
                     err, block_start, block_stop);
             return err;
         }
 
         /* reset start and stop after processing a region */
         block_start = ~0ULL;
     }
 
     return blkdev_issue_flush(journal->j_dev);
 }
 
 /**
  * jbd2_journal_update_sb_errno() - Update error in the journal.
  * @journal: The journal to update.
  *
  * Update a journal's errno.  Write updated superblock to disk waiting for IO
  * to complete.
  */
 void jbd2_journal_update_sb_errno(journal_t *journal)
 {
     journal_superblock_t *sb = journal->j_superblock;
     int errcode;
 
     lock_buffer(journal->j_sb_buffer);
     errcode = journal->j_errno;
     if (errcode == -ESHUTDOWN)
         errcode = 0;
     jbd2_debug(1, "JBD2: updating superblock error (errno %d)\n", errcode);
     sb->s_errno    = cpu_to_be32(errcode);
 
     jbd2_write_superblock(journal, REQ_SYNC | REQ_FUA);
 }
 EXPORT_SYMBOL(jbd2_journal_update_sb_errno);
 
 static int journal_revoke_records_per_block(journal_t *journal)
 {
     int record_size;
     int space = journal->j_blocksize - sizeof(jbd2_journal_revoke_header_t);
 
     if (jbd2_has_feature_64bit(journal))
         record_size = 8;
     else
         record_size = 4;
 
     if (jbd2_journal_has_csum_v2or3(journal))
         space -= sizeof(struct jbd2_journal_block_tail);
     return space / record_size;
 }
 
 /*
  * Read the superblock for a given journal, performing initial
  * validation of the format.
  */
 static int journal_get_superblock(journal_t *journal)
 {
     struct buffer_head *bh;
     journal_superblock_t *sb;
     int err = -EIO;
 
     bh = journal->j_sb_buffer;
 
     J_ASSERT(bh != NULL);
     if (!buffer_uptodate(bh)) {
         ll_rw_block(REQ_OP_READ, 1, &bh);
         wait_on_buffer(bh);
         if (!buffer_uptodate(bh)) {
             printk(KERN_ERR
                 "JBD2: IO error reading journal superblock\n");
             goto out;
         }
     }
 
     if (buffer_verified(bh))
         return 0;
 
     sb = journal->j_superblock;
 
     err = -EINVAL;
 
     if (sb->s_header.h_magic != cpu_to_be32(JBD2_MAGIC_NUMBER) ||
         sb->s_blocksize != cpu_to_be32(journal->j_blocksize)) {
         printk(KERN_WARNING "JBD2: no valid journal superblock found\n");
         goto out;
     }
 
     switch(be32_to_cpu(sb->s_header.h_blocktype)) {
     case JBD2_SUPERBLOCK_V1:
         journal->j_format_version = 1;
         break;
     case JBD2_SUPERBLOCK_V2:
         journal->j_format_version = 2;
         break;
     default:
         printk(KERN_WARNING "JBD2: unrecognised superblock format ID\n");
         goto out;
     }
 
     if (be32_to_cpu(sb->s_maxlen) < journal->j_total_len)
         journal->j_total_len = be32_to_cpu(sb->s_maxlen);
     else if (be32_to_cpu(sb->s_maxlen) > journal->j_total_len) {
         printk(KERN_WARNING "JBD2: journal file too short\n");
         goto out;
     }
 
     if (be32_to_cpu(sb->s_first) == 0 ||
         be32_to_cpu(sb->s_first) >= journal->j_total_len) {
         printk(KERN_WARNING
             "JBD2: Invalid start block of journal: %u\n",
             be32_to_cpu(sb->s_first));
         goto out;
     }
 
     if (jbd2_has_feature_csum2(journal) &&
         jbd2_has_feature_csum3(journal)) {
         /* Can't have checksum v2 and v3 at the same time! */
         printk(KERN_ERR "JBD2: Can't enable checksumming v2 and v3 "
                "at the same time!\n");
         goto out;
     }
 
     if (jbd2_journal_has_csum_v2or3_feature(journal) &&
         jbd2_has_feature_checksum(journal)) {
         /* Can't have checksum v1 and v2 on at the same time! */
         printk(KERN_ERR "JBD2: Can't enable checksumming v1 and v2/3 "
                "at the same time!\n");
         goto out;
     }
 
     if (!jbd2_verify_csum_type(journal, sb)) {
         printk(KERN_ERR "JBD2: Unknown checksum type\n");
         goto out;
     }
 
     /* Load the checksum driver */
     if (jbd2_journal_has_csum_v2or3_feature(journal)) {
         journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
         if (IS_ERR(journal->j_chksum_driver)) {
             printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
             err = PTR_ERR(journal->j_chksum_driver);
             journal->j_chksum_driver = NULL;
             goto out;
         }
     }
 
     if (jbd2_journal_has_csum_v2or3(journal)) {
         /* Check superblock checksum */
         if (sb->s_checksum != jbd2_superblock_csum(journal, sb)) {
             printk(KERN_ERR "JBD2: journal checksum error\n");
             err = -EFSBADCRC;
             goto out;
         }
 
         /* Precompute checksum seed for all metadata */
         journal->j_csum_seed = jbd2_chksum(journal, ~0, sb->s_uuid,
                            sizeof(sb->s_uuid));
     }
 
     journal->j_revoke_records_per_block =
                 journal_revoke_records_per_block(journal);
     set_buffer_verified(bh);
 
     return 0;
 
 out:
     journal_fail_superblock(journal);
     return err;
 }
 
 /*
  * Load the on-disk journal superblock and read the key fields into the
  * journal_t.
  */
 
 static int load_superblock(journal_t *journal)
 {
     int err;
     journal_superblock_t *sb;
     int num_fc_blocks;
 
     err = journal_get_superblock(journal);
     if (err)
         return err;
 
     sb = journal->j_superblock;
 
     journal->j_tail_sequence = be32_to_cpu(sb->s_sequence);
     journal->j_tail = be32_to_cpu(sb->s_start);
     journal->j_first = be32_to_cpu(sb->s_first);
     journal->j_errno = be32_to_cpu(sb->s_errno);
     journal->j_last = be32_to_cpu(sb->s_maxlen);
 
     if (jbd2_has_feature_fast_commit(journal)) {
         journal->j_fc_last = be32_to_cpu(sb->s_maxlen);
         num_fc_blocks = jbd2_journal_get_num_fc_blks(sb);
         if (journal->j_last - num_fc_blocks >= JBD2_MIN_JOURNAL_BLOCKS)
             journal->j_last = journal->j_fc_last - num_fc_blocks;
         journal->j_fc_first = journal->j_last + 1;
         journal->j_fc_off = 0;
     }
 
     return 0;
 }
 
 
 /**
  * jbd2_journal_load() - Read journal from disk.
  * @journal: Journal to act on.
  *
  * Given a journal_t structure which tells us which disk blocks contain
  * a journal, read the journal from disk to initialise the in-memory
  * structures.
  */
 int jbd2_journal_load(journal_t *journal)
 {
     int err;
     journal_superblock_t *sb;
 
     err = load_superblock(journal);
     if (err)
         return err;
 
     sb = journal->j_superblock;
     /* If this is a V2 superblock, then we have to check the
      * features flags on it. */
 
     if (journal->j_format_version >= 2) {
         if ((sb->s_feature_ro_compat &
              ~cpu_to_be32(JBD2_KNOWN_ROCOMPAT_FEATURES)) ||
             (sb->s_feature_incompat &
              ~cpu_to_be32(JBD2_KNOWN_INCOMPAT_FEATURES))) {
             printk(KERN_WARNING
                 "JBD2: Unrecognised features on journal\n");
             return -EINVAL;
         }
     }
 
     /*
      * Create a slab for this blocksize
      */
     err = jbd2_journal_create_slab(be32_to_cpu(sb->s_blocksize));
     if (err)
         return err;
 
     /* Let the recovery code check whether it needs to recover any
      * data from the journal. */
     if (jbd2_journal_recover(journal))
         goto recovery_error;
 
     if (journal->j_failed_commit) {
         printk(KERN_ERR "JBD2: journal transaction %u on %s "
                "is corrupt.\n", journal->j_failed_commit,
                journal->j_devname);
         return -EFSCORRUPTED;
     }
     /*
      * clear JBD2_ABORT flag initialized in journal_init_common
      * here to update log tail information with the newest seq.
      */
     journal->j_flags &= ~JBD2_ABORT;
 
     /* OK, we've finished with the dynamic journal bits:
      * reinitialise the dynamic contents of the superblock in memory
      * and reset them on disk. */
     if (journal_reset(journal))
         goto recovery_error;
 
     journal->j_flags |= JBD2_LOADED;
     return 0;
 
 recovery_error:
     printk(KERN_WARNING "JBD2: recovery failed\n");
     return -EIO;
 }
 
 /**
  * jbd2_journal_destroy() - Release a journal_t structure.
  * @journal: Journal to act on.
  *
  * Release a journal_t structure once it is no longer in use by the
  * journaled object.
  * Return <0 if we couldn't clean up the journal.
  */
 int jbd2_journal_destroy(journal_t *journal)
 {
     int err = 0;
 
     /* Wait for the commit thread to wake up and die. */
     journal_kill_thread(journal);
 
     /* Force a final log commit */
     if (journal->j_running_transaction)
         jbd2_journal_commit_transaction(journal);
 
     /* Force any old transactions to disk */
 
     /* Totally anal locking here... */
     spin_lock(&journal->j_list_lock);
     while (journal->j_checkpoint_transactions != NULL) {
         spin_unlock(&journal->j_list_lock);
         mutex_lock_io(&journal->j_checkpoint_mutex);
         err = jbd2_log_do_checkpoint(journal);
         mutex_unlock(&journal->j_checkpoint_mutex);
         /*
          * If checkpointing failed, just free the buffers to avoid
          * looping forever
          */
         if (err) {
             jbd2_journal_destroy_checkpoint(journal);
             spin_lock(&journal->j_list_lock);
             break;
         }
         spin_lock(&journal->j_list_lock);
     }
 
     J_ASSERT(journal->j_running_transaction == NULL);
     J_ASSERT(journal->j_committing_transaction == NULL);
     J_ASSERT(journal->j_checkpoint_transactions == NULL);
     spin_unlock(&journal->j_list_lock);
 
     /*
      * OK, all checkpoint transactions have been checked, now check the
      * write out io error flag and abort the journal if some buffer failed
      * to write back to the original location, otherwise the filesystem
      * may become inconsistent.
      */
     if (!is_journal_aborted(journal) &&
         test_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags))
         jbd2_journal_abort(journal, -EIO);
 
     if (journal->j_sb_buffer) {
         if (!is_journal_aborted(journal)) {
             mutex_lock_io(&journal->j_checkpoint_mutex);
 
             write_lock(&journal->j_state_lock);
             journal->j_tail_sequence =
                 ++journal->j_transaction_sequence;
             write_unlock(&journal->j_state_lock);
 
             jbd2_mark_journal_empty(journal,
                     REQ_SYNC | REQ_PREFLUSH | REQ_FUA);
             mutex_unlock(&journal->j_checkpoint_mutex);
         } else
             err = -EIO;
         brelse(journal->j_sb_buffer);
     }
 
     if (journal->j_shrinker.flags & SHRINKER_REGISTERED) {
         percpu_counter_destroy(&journal->j_checkpoint_jh_count);
         unregister_shrinker(&journal->j_shrinker);
     }
     if (journal->j_proc_entry)
         jbd2_stats_proc_exit(journal);
     iput(journal->j_inode);
     if (journal->j_revoke)
         jbd2_journal_destroy_revoke(journal);
     if (journal->j_chksum_driver)
         crypto_free_shash(journal->j_chksum_driver);
     kfree(journal->j_fc_wbuf);
     kfree(journal->j_wbuf);
     kfree(journal);
 
     return err;
 }
 
 
 /**
  * jbd2_journal_check_used_features() - Check if features specified are used.
  * @journal: Journal to check.
  * @compat: bitmask of compatible features
  * @ro: bitmask of features that force read-only mount
  * @incompat: bitmask of incompatible features
  *
  * Check whether the journal uses all of a given set of
  * features.  Return true (non-zero) if it does.
  **/
 
 int jbd2_journal_check_used_features(journal_t *journal, unsigned long compat,
                  unsigned long ro, unsigned long incompat)
 {
     journal_superblock_t *sb;
 
     if (!compat && !ro && !incompat)
         return 1;
     /* Load journal superblock if it is not loaded yet. */
     if (journal->j_format_version == 0 &&
         journal_get_superblock(journal) != 0)
         return 0;
     if (journal->j_format_version == 1)
         return 0;
 
     sb = journal->j_superblock;
 
     if (((be32_to_cpu(sb->s_feature_compat) & compat) == compat) &&
         ((be32_to_cpu(sb->s_feature_ro_compat) & ro) == ro) &&
         ((be32_to_cpu(sb->s_feature_incompat) & incompat) == incompat))
         return 1;
 
     return 0;
 }
 
 /**
  * jbd2_journal_check_available_features() - Check feature set in journalling layer
  * @journal: Journal to check.
  * @compat: bitmask of compatible features
  * @ro: bitmask of features that force read-only mount
  * @incompat: bitmask of incompatible features
  *
  * Check whether the journaling code supports the use of
  * all of a given set of features on this journal.  Return true
  * (non-zero) if it can. */
 
 int jbd2_journal_check_available_features(journal_t *journal, unsigned long compat,
                       unsigned long ro, unsigned long incompat)
 {
     if (!compat && !ro && !incompat)
         return 1;
 
     /* We can support any known requested features iff the
      * superblock is in version 2.  Otherwise we fail to support any
      * extended sb features. */
 
     if (journal->j_format_version != 2)
         return 0;
 
     if ((compat   & JBD2_KNOWN_COMPAT_FEATURES) == compat &&
         (ro       & JBD2_KNOWN_ROCOMPAT_FEATURES) == ro &&
         (incompat & JBD2_KNOWN_INCOMPAT_FEATURES) == incompat)
         return 1;
 
     return 0;
 }
 
 static int
 jbd2_journal_initialize_fast_commit(journal_t *journal)
 {
     journal_superblock_t *sb = journal->j_superblock;
     unsigned long long num_fc_blks;
 
     num_fc_blks = jbd2_journal_get_num_fc_blks(sb);
     if (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS)
         return -ENOSPC;
 
     /* Are we called twice? */
     WARN_ON(journal->j_fc_wbuf != NULL);
     journal->j_fc_wbuf = kmalloc_array(num_fc_blks,
                 sizeof(struct buffer_head *), GFP_KERNEL);
     if (!journal->j_fc_wbuf)
         return -ENOMEM;
 
     journal->j_fc_wbufsize = num_fc_blks;
     journal->j_fc_last = journal->j_last;
     journal->j_last = journal->j_fc_last - num_fc_blks;
     journal->j_fc_first = journal->j_last + 1;
     journal->j_fc_off = 0;
     journal->j_free = journal->j_last - journal->j_first;
     journal->j_max_transaction_buffers =
         jbd2_journal_get_max_txn_bufs(journal);
 
     return 0;
 }
 
 /**
  * jbd2_journal_set_features() - Mark a given journal feature in the superblock
  * @journal: Journal to act on.
  * @compat: bitmask of compatible features
  * @ro: bitmask of features that force read-only mount
  * @incompat: bitmask of incompatible features
  *
  * Mark a given journal feature as present on the
  * superblock.  Returns true if the requested features could be set.
  *
  */
 
 int jbd2_journal_set_features(journal_t *journal, unsigned long compat,
               unsigned long ro, unsigned long incompat)
 {
 #define INCOMPAT_FEATURE_ON(f) \
         ((incompat & (f)) && !(sb->s_feature_incompat & cpu_to_be32(f)))
 #define COMPAT_FEATURE_ON(f) \
         ((compat & (f)) && !(sb->s_feature_compat & cpu_to_be32(f)))
     journal_superblock_t *sb;
 
     if (jbd2_journal_check_used_features(journal, compat, ro, incompat))
         return 1;
 
     if (!jbd2_journal_check_available_features(journal, compat, ro, incompat))
         return 0;
 
     /* If enabling v2 checksums, turn on v3 instead */
     if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V2) {
         incompat &= ~JBD2_FEATURE_INCOMPAT_CSUM_V2;
         incompat |= JBD2_FEATURE_INCOMPAT_CSUM_V3;
     }
 
     /* Asking for checksumming v3 and v1?  Only give them v3. */
     if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V3 &&
         compat & JBD2_FEATURE_COMPAT_CHECKSUM)
         compat &= ~JBD2_FEATURE_COMPAT_CHECKSUM;
 
     jbd2_debug(1, "Setting new features 0x%lx/0x%lx/0x%lx\n",
           compat, ro, incompat);
 
     sb = journal->j_superblock;
 
     if (incompat & JBD2_FEATURE_INCOMPAT_FAST_COMMIT) {
         if (jbd2_journal_initialize_fast_commit(journal)) {
             pr_err("JBD2: Cannot enable fast commits.\n");
             return 0;
         }
     }
 
     /* Load the checksum driver if necessary */
     if ((journal->j_chksum_driver == NULL) &&
         INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
         journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
         if (IS_ERR(journal->j_chksum_driver)) {
             printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
             journal->j_chksum_driver = NULL;
             return 0;
         }
         /* Precompute checksum seed for all metadata */
         journal->j_csum_seed = jbd2_chksum(journal, ~0, sb->s_uuid,
                            sizeof(sb->s_uuid));
     }
 
     lock_buffer(journal->j_sb_buffer);
 
     /* If enabling v3 checksums, update superblock */
     if (INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
         sb->s_checksum_type = JBD2_CRC32C_CHKSUM;
         sb->s_feature_compat &=
             ~cpu_to_be32(JBD2_FEATURE_COMPAT_CHECKSUM);
     }
 
     /* If enabling v1 checksums, downgrade superblock */
     if (COMPAT_FEATURE_ON(JBD2_FEATURE_COMPAT_CHECKSUM))
         sb->s_feature_incompat &=
             ~cpu_to_be32(JBD2_FEATURE_INCOMPAT_CSUM_V2 |
                      JBD2_FEATURE_INCOMPAT_CSUM_V3);
 
     sb->s_feature_compat    |= cpu_to_be32(compat);
     sb->s_feature_ro_compat |= cpu_to_be32(ro);
     sb->s_feature_incompat  |= cpu_to_be32(incompat);
     unlock_buffer(journal->j_sb_buffer);
     journal->j_revoke_records_per_block =
                 journal_revoke_records_per_block(journal);
 
     return 1;
 #undef COMPAT_FEATURE_ON
 #undef INCOMPAT_FEATURE_ON
 }
 
 /*
  * jbd2_journal_clear_features() - Clear a given journal feature in the
  *                  superblock
  * @journal: Journal to act on.
  * @compat: bitmask of compatible features
  * @ro: bitmask of features that force read-only mount
  * @incompat: bitmask of incompatible features
  *
  * Clear a given journal feature as present on the
  * superblock.
  */
 void jbd2_journal_clear_features(journal_t *journal, unsigned long compat,
                 unsigned long ro, unsigned long incompat)
 {
     journal_superblock_t *sb;
 
     jbd2_debug(1, "Clear features 0x%lx/0x%lx/0x%lx\n",
           compat, ro, incompat);
 
     sb = journal->j_superblock;
 
     sb->s_feature_compat    &= ~cpu_to_be32(compat);
     sb->s_feature_ro_compat &= ~cpu_to_be32(ro);
     sb->s_feature_incompat  &= ~cpu_to_be32(incompat);
     journal->j_revoke_records_per_block =
                 journal_revoke_records_per_block(journal);
 }
 EXPORT_SYMBOL(jbd2_journal_clear_features);
 
 /**
  * jbd2_journal_flush() - Flush journal
  * @journal: Journal to act on.
  * @flags: optional operation on the journal blocks after the flush (see below)
  *
  * Flush all data for a given journal to disk and empty the journal.
  * Filesystems can use this when remounting readonly to ensure that
  * recovery does not need to happen on remount. Optionally, a discard or zeroout
  * can be issued on the journal blocks after flushing.
  *
  * flags:
  *  JBD2_JOURNAL_FLUSH_DISCARD: issues discards for the journal blocks
  *  JBD2_JOURNAL_FLUSH_ZEROOUT: issues zeroouts for the journal blocks
  */
 int jbd2_journal_flush(journal_t *journal, unsigned int flags)
 {
     int err = 0;
     transaction_t *transaction = NULL;
 
     write_lock(&journal->j_state_lock);
 
     /* Force everything buffered to the log... */
     if (journal->j_running_transaction) {
         transaction = journal->j_running_transaction;
         __jbd2_log_start_commit(journal, transaction->t_tid);
     } else if (journal->j_committing_transaction)
         transaction = journal->j_committing_transaction;
 
     /* Wait for the log commit to complete... */
     if (transaction) {
         tid_t tid = transaction->t_tid;
 
         write_unlock(&journal->j_state_lock);
         jbd2_log_wait_commit(journal, tid);
     } else {
         write_unlock(&journal->j_state_lock);
     }
 
     /* ...and flush everything in the log out to disk. */
     spin_lock(&journal->j_list_lock);
     while (!err && journal->j_checkpoint_transactions != NULL) {
         spin_unlock(&journal->j_list_lock);
         mutex_lock_io(&journal->j_checkpoint_mutex);
         err = jbd2_log_do_checkpoint(journal);
         mutex_unlock(&journal->j_checkpoint_mutex);
         spin_lock(&journal->j_list_lock);
     }
     spin_unlock(&journal->j_list_lock);
 
     if (is_journal_aborted(journal))
         return -EIO;
 
     mutex_lock_io(&journal->j_checkpoint_mutex);
     if (!err) {
         err = jbd2_cleanup_journal_tail(journal);
         if (err < 0) {
             mutex_unlock(&journal->j_checkpoint_mutex);
             goto out;
         }
         err = 0;
     }
 
     /* Finally, mark the journal as really needing no recovery.
      * This sets s_start==0 in the underlying superblock, which is
      * the magic code for a fully-recovered superblock.  Any future
      * commits of data to the journal will restore the current
      * s_start value. */
     jbd2_mark_journal_empty(journal, REQ_SYNC | REQ_FUA);
 
     if (flags)
         err = __jbd2_journal_erase(journal, flags);
 
     mutex_unlock(&journal->j_checkpoint_mutex);
     write_lock(&journal->j_state_lock);
     J_ASSERT(!journal->j_running_transaction);
     J_ASSERT(!journal->j_committing_transaction);
     J_ASSERT(!journal->j_checkpoint_transactions);
     J_ASSERT(journal->j_head == journal->j_tail);
     J_ASSERT(journal->j_tail_sequence == journal->j_transaction_sequence);
     write_unlock(&journal->j_state_lock);
 out:
     return err;
 }
 
 /**
  * jbd2_journal_wipe() - Wipe journal contents
  * @journal: Journal to act on.
  * @write: flag (see below)
  *
  * Wipe out all of the contents of a journal, safely.  This will produce
  * a warning if the journal contains any valid recovery information.
  * Must be called between journal_init_*() and jbd2_journal_load().
  *
  * If 'write' is non-zero, then we wipe out the journal on disk; otherwise
  * we merely suppress recovery.
  */
 
 int jbd2_journal_wipe(journal_t *journal, int write)
 {
     int err = 0;
 
     J_ASSERT (!(journal->j_flags & JBD2_LOADED));
 
     err = load_superblock(journal);
     if (err)
         return err;
 
     if (!journal->j_tail)
         goto no_recovery;
 
     printk(KERN_WARNING "JBD2: %s recovery information on journal\n",
         write ? "Clearing" : "Ignoring");
 
     err = jbd2_journal_skip_recovery(journal);
     if (write) {
         /* Lock to make assertions happy... */
         mutex_lock_io(&journal->j_checkpoint_mutex);
         jbd2_mark_journal_empty(journal, REQ_SYNC | REQ_FUA);
         mutex_unlock(&journal->j_checkpoint_mutex);
     }
 
  no_recovery:
     return err;
 }
 
 /**
  * jbd2_journal_abort () - Shutdown the journal immediately.
  * @journal: the journal to shutdown.
  * @errno:   an error number to record in the journal indicating
  *           the reason for the shutdown.
  *
  * Perform a complete, immediate shutdown of the ENTIRE
  * journal (not of a single transaction).  This operation cannot be
  * undone without closing and reopening the journal.
  *
  * The jbd2_journal_abort function is intended to support higher level error
  * recovery mechanisms such as the ext2/ext3 remount-readonly error
  * mode.
  *
  * Journal abort has very specific semantics.  Any existing dirty,
  * unjournaled buffers in the main filesystem will still be written to
  * disk by bdflush, but the journaling mechanism will be suspended
  * immediately and no further transaction commits will be honoured.
  *
  * Any dirty, journaled buffers will be written back to disk without
  * hitting the journal.  Atomicity cannot be guaranteed on an aborted
  * filesystem, but we _do_ attempt to leave as much data as possible
  * behind for fsck to use for cleanup.
  *
  * Any attempt to get a new transaction handle on a journal which is in
  * ABORT state will just result in an -EROFS error return.  A
  * jbd2_journal_stop on an existing handle will return -EIO if we have
  * entered abort state during the update.
  *
  * Recursive transactions are not disturbed by journal abort until the
  * final jbd2_journal_stop, which will receive the -EIO error.
  *
  * Finally, the jbd2_journal_abort call allows the caller to supply an errno
  * which will be recorded (if possible) in the journal superblock.  This
  * allows a client to record failure conditions in the middle of a
  * transaction without having to complete the transaction to record the
  * failure to disk.  ext3_error, for example, now uses this
  * functionality.
  *
  */
 
 void jbd2_journal_abort(journal_t *journal, int errno)
 {
     transaction_t *transaction;
 
     /*
      * Lock the aborting procedure until everything is done, this avoid
      * races between filesystem's error handling flow (e.g. ext4_abort()),
      * ensure panic after the error info is written into journal's
      * superblock.
      */
     mutex_lock(&journal->j_abort_mutex);
     /*
      * ESHUTDOWN always takes precedence because a file system check
      * caused by any other journal abort error is not required after
      * a shutdown triggered.
      */
     write_lock(&journal->j_state_lock);
     if (journal->j_flags & JBD2_ABORT) {
         int old_errno = journal->j_errno;
 
         write_unlock(&journal->j_state_lock);
         if (old_errno != -ESHUTDOWN && errno == -ESHUTDOWN) {
             journal->j_errno = errno;
             jbd2_journal_update_sb_errno(journal);
         }
         mutex_unlock(&journal->j_abort_mutex);
         return;
     }
 
     /*
      * Mark the abort as occurred and start current running transaction
      * to release all journaled buffer.
      */
     pr_err("Aborting journal on device %s.\n", journal->j_devname);
 
     journal->j_flags |= JBD2_ABORT;
     journal->j_errno = errno;
     transaction = journal->j_running_transaction;
     if (transaction)
         __jbd2_log_start_commit(journal, transaction->t_tid);
     write_unlock(&journal->j_state_lock);
 
     /*
      * Record errno to the journal super block, so that fsck and jbd2
      * layer could realise that a filesystem check is needed.
      */
     jbd2_journal_update_sb_errno(journal);
     mutex_unlock(&journal->j_abort_mutex);
 }
 
 /**
  * jbd2_journal_errno() - returns the journal's error state.
  * @journal: journal to examine.
  *
  * This is the errno number set with jbd2_journal_abort(), the last
  * time the journal was mounted - if the journal was stopped
  * without calling abort this will be 0.
  *
  * If the journal has been aborted on this mount time -EROFS will
  * be returned.
  */
 int jbd2_journal_errno(journal_t *journal)
 {
     int err;
 
     read_lock(&journal->j_state_lock);
     if (journal->j_flags & JBD2_ABORT)
         err = -EROFS;
     else
         err = journal->j_errno;
     read_unlock(&journal->j_state_lock);
     return err;
 }
 
 /**
  * jbd2_journal_clear_err() - clears the journal's error state
  * @journal: journal to act on.
  *
  * An error must be cleared or acked to take a FS out of readonly
  * mode.
  */
 int jbd2_journal_clear_err(journal_t *journal)
 {
     int err = 0;
 
     write_lock(&journal->j_state_lock);
     if (journal->j_flags & JBD2_ABORT)
         err = -EROFS;
     else
         journal->j_errno = 0;
     write_unlock(&journal->j_state_lock);
     return err;
 }
 
 /**
  * jbd2_journal_ack_err() - Ack journal err.
  * @journal: journal to act on.
  *
  * An error must be cleared or acked to take a FS out of readonly
  * mode.
  */
 void jbd2_journal_ack_err(journal_t *journal)
 {
     write_lock(&journal->j_state_lock);
     if (journal->j_errno)
         journal->j_flags |= JBD2_ACK_ERR;
     write_unlock(&journal->j_state_lock);
 }
 
 int jbd2_journal_blocks_per_page(struct inode *inode)
 {
     return 1 << (PAGE_SHIFT - inode->i_sb->s_blocksize_bits);
 }
 
 /*
  * helper functions to deal with 32 or 64bit block numbers.
  */
 size_t journal_tag_bytes(journal_t *journal)
 {
     size_t sz;
 
     if (jbd2_has_feature_csum3(journal))
         return sizeof(journal_block_tag3_t);
 
     sz = sizeof(journal_block_tag_t);
 
     if (jbd2_has_feature_csum2(journal))
         sz += sizeof(__u16);
 
     if (jbd2_has_feature_64bit(journal))
         return sz;
     else
         return sz - sizeof(__u32);
 }
 
 /*
  * JBD memory management
  *
  * These functions are used to allocate block-sized chunks of memory
  * used for making copies of buffer_head data.  Very often it will be
  * page-sized chunks of data, but sometimes it will be in
  * sub-page-size chunks.  (For example, 16k pages on Power systems
  * with a 4k block file system.)  For blocks smaller than a page, we
  * use a SLAB allocator.  There are slab caches for each block size,
  * which are allocated at mount time, if necessary, and we only free
  * (all of) the slab caches when/if the jbd2 module is unloaded.  For
  * this reason we don't need to a mutex to protect access to
  * jbd2_slab[] allocating or releasing memory; only in
  * jbd2_journal_create_slab().
  */
 #define JBD2_MAX_SLABS 8
 static struct kmem_cache *jbd2_slab[JBD2_MAX_SLABS];
 
 static const char *jbd2_slab_names[JBD2_MAX_SLABS] = {
     "jbd2_1k", "jbd2_2k", "jbd2_4k", "jbd2_8k",
     "jbd2_16k", "jbd2_32k", "jbd2_64k", "jbd2_128k"
 };
 
 
 static void jbd2_journal_destroy_slabs(void)
 {
     int i;
 
     for (i = 0; i < JBD2_MAX_SLABS; i++) {
         kmem_cache_destroy(jbd2_slab[i]);
         jbd2_slab[i] = NULL;
     }
 }
 
 static int jbd2_journal_create_slab(size_t size)
 {
     static DEFINE_MUTEX(jbd2_slab_create_mutex);
     int i = order_base_2(size) - 10;
     size_t slab_size;
 
     if (size == PAGE_SIZE)
         return 0;
 
     if (i >= JBD2_MAX_SLABS)
         return -EINVAL;
 
     if (unlikely(i < 0))
         i = 0;
     mutex_lock(&jbd2_slab_create_mutex);
     if (jbd2_slab[i]) {
         mutex_unlock(&jbd2_slab_create_mutex);
         return 0;   /* Already created */
     }
 
     slab_size = 1 << (i+10);
     jbd2_slab[i] = kmem_cache_create(jbd2_slab_names[i], slab_size,
                      slab_size, 0, NULL);
     mutex_unlock(&jbd2_slab_create_mutex);
     if (!jbd2_slab[i]) {
         printk(KERN_EMERG "JBD2: no memory for jbd2_slab cache\n");
         return -ENOMEM;
     }
     return 0;
 }
 
 static struct kmem_cache *get_slab(size_t size)
 {
     int i = order_base_2(size) - 10;
 
     BUG_ON(i >= JBD2_MAX_SLABS);
     if (unlikely(i < 0))
         i = 0;
     BUG_ON(jbd2_slab[i] == NULL);
     return jbd2_slab[i];
 }
 
 void *jbd2_alloc(size_t size, gfp_t flags)
 {
     void *ptr;
 
     BUG_ON(size & (size-1)); /* Must be a power of 2 */
 
     if (size < PAGE_SIZE)
         ptr = kmem_cache_alloc(get_slab(size), flags);
     else
         ptr = (void *)__get_free_pages(flags, get_order(size));
 
     /* Check alignment; SLUB has gotten this wrong in the past,
      * and this can lead to user data corruption! */
     BUG_ON(((unsigned long) ptr) & (size-1));
 
     return ptr;
 }
 
 void jbd2_free(void *ptr, size_t size)
 {
     if (size < PAGE_SIZE)
         kmem_cache_free(get_slab(size), ptr);
     else
         free_pages((unsigned long)ptr, get_order(size));
 };
 
 /*
  * Journal_head storage management
  */
 static struct kmem_cache *jbd2_journal_head_cache;
 #ifdef CONFIG_JBD2_DEBUG
 static atomic_t nr_journal_heads = ATOMIC_INIT(0);
 #endif
 
 static int __init jbd2_journal_init_journal_head_cache(void)
 {
     J_ASSERT(!jbd2_journal_head_cache);
     jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
                 sizeof(struct journal_head),
                 0,      /* offset */
                 SLAB_TEMPORARY | SLAB_TYPESAFE_BY_RCU,
                 NULL);      /* ctor */
     if (!jbd2_journal_head_cache) {
         printk(KERN_EMERG "JBD2: no memory for journal_head cache\n");
         return -ENOMEM;
     }
     return 0;
 }
 
 static void jbd2_journal_destroy_journal_head_cache(void)
 {
     kmem_cache_destroy(jbd2_journal_head_cache);
     jbd2_journal_head_cache = NULL;
 }
 
 /*
  * journal_head splicing and dicing
  */
 static struct journal_head *journal_alloc_journal_head(void)
 {
     struct journal_head *ret;
 
 #ifdef CONFIG_JBD2_DEBUG
     atomic_inc(&nr_journal_heads);
 #endif
     ret = kmem_cache_zalloc(jbd2_journal_head_cache, GFP_NOFS);
     if (!ret) {
         jbd2_debug(1, "out of memory for journal_head\n");
         pr_notice_ratelimited("ENOMEM in %s, retrying.\n", __func__);
         ret = kmem_cache_zalloc(jbd2_journal_head_cache,
                 GFP_NOFS | __GFP_NOFAIL);
     }
     if (ret)
         spin_lock_init(&ret->b_state_lock);
     return ret;
 }
 
 static void journal_free_journal_head(struct journal_head *jh)
 {
 #ifdef CONFIG_JBD2_DEBUG
     atomic_dec(&nr_journal_heads);
     memset(jh, JBD2_POISON_FREE, sizeof(*jh));
 #endif
     kmem_cache_free(jbd2_journal_head_cache, jh);
 }
 
 /*
  * A journal_head is attached to a buffer_head whenever JBD has an
  * interest in the buffer.
  *
  * Whenever a buffer has an attached journal_head, its ->b_state:BH_JBD bit
  * is set.  This bit is tested in core kernel code where we need to take
  * JBD-specific actions.  Testing the zeroness of ->b_private is not reliable
  * there.
  *
  * When a buffer has its BH_JBD bit set, its ->b_count is elevated by one.
  *
  * When a buffer has its BH_JBD bit set it is immune from being released by
  * core kernel code, mainly via ->b_count.
  *
  * A journal_head is detached from its buffer_head when the journal_head's
  * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
  * transaction (b_cp_transaction) hold their references to b_jcount.
  *
  * Various places in the kernel want to attach a journal_head to a buffer_head
  * _before_ attaching the journal_head to a transaction.  To protect the
  * journal_head in this situation, jbd2_journal_add_journal_head elevates the
  * journal_head's b_jcount refcount by one.  The caller must call
  * jbd2_journal_put_journal_head() to undo this.
  *
  * So the typical usage would be:
  *
  *  (Attach a journal_head if needed.  Increments b_jcount)
  *  struct journal_head *jh = jbd2_journal_add_journal_head(bh);
  *  ...
  *      (Get another reference for transaction)
  *  jbd2_journal_grab_journal_head(bh);
  *  jh->b_transaction = xxx;
  *  (Put original reference)
  *  jbd2_journal_put_journal_head(jh);
  */
 
 /*
  * Give a buffer_head a journal_head.
  *
  * May sleep.
  */
 struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh)
 {
     struct journal_head *jh;
     struct journal_head *new_jh = NULL;
 
 repeat:
     if (!buffer_jbd(bh))
         new_jh = journal_alloc_journal_head();
 
     jbd_lock_bh_journal_head(bh);
     if (buffer_jbd(bh)) {
         jh = bh2jh(bh);
     } else {
         J_ASSERT_BH(bh,
             (atomic_read(&bh->b_count) > 0) ||
             (bh->b_page && bh->b_page->mapping));
 
         if (!new_jh) {
             jbd_unlock_bh_journal_head(bh);
             goto repeat;
         }
 
         jh = new_jh;
         new_jh = NULL;      /* We consumed it */
         set_buffer_jbd(bh);
         bh->b_private = jh;
         jh->b_bh = bh;
         get_bh(bh);
         BUFFER_TRACE(bh, "added journal_head");
     }
     jh->b_jcount++;
     jbd_unlock_bh_journal_head(bh);
     if (new_jh)
         journal_free_journal_head(new_jh);
     return bh->b_private;
 }
 
 /*
  * Grab a ref against this buffer_head's journal_head.  If it ended up not
  * having a journal_head, return NULL
  */
 struct journal_head *jbd2_journal_grab_journal_head(struct buffer_head *bh)
 {
     struct journal_head *jh = NULL;
 
     jbd_lock_bh_journal_head(bh);
     if (buffer_jbd(bh)) {
         jh = bh2jh(bh);
         jh->b_jcount++;
     }
     jbd_unlock_bh_journal_head(bh);
     return jh;
 }
 EXPORT_SYMBOL(jbd2_journal_grab_journal_head);
 
 static void __journal_remove_journal_head(struct buffer_head *bh)
 {
     struct journal_head *jh = bh2jh(bh);
 
     J_ASSERT_JH(jh, jh->b_transaction == NULL);
     J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
     J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
     J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
     J_ASSERT_BH(bh, buffer_jbd(bh));
     J_ASSERT_BH(bh, jh2bh(jh) == bh);
     BUFFER_TRACE(bh, "remove journal_head");
 
     /* Unlink before dropping the lock */
     bh->b_private = NULL;
     jh->b_bh = NULL;    /* debug, really */
     clear_buffer_jbd(bh);
 }
 
 static void journal_release_journal_head(struct journal_head *jh, size_t b_size)
 {
     if (jh->b_frozen_data) {
         printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
         jbd2_free(jh->b_frozen_data, b_size);
     }
     if (jh->b_committed_data) {
         printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
         jbd2_free(jh->b_committed_data, b_size);
     }
     journal_free_journal_head(jh);
 }
 
 /*
  * Drop a reference on the passed journal_head.  If it fell to zero then
  * release the journal_head from the buffer_head.
  */
 void jbd2_journal_put_journal_head(struct journal_head *jh)
 {
     struct buffer_head *bh = jh2bh(jh);
 
     jbd_lock_bh_journal_head(bh);
     J_ASSERT_JH(jh, jh->b_jcount > 0);
     --jh->b_jcount;
     if (!jh->b_jcount) {
         __journal_remove_journal_head(bh);
         jbd_unlock_bh_journal_head(bh);
         journal_release_journal_head(jh, bh->b_size);
         __brelse(bh);
     } else {
         jbd_unlock_bh_journal_head(bh);
     }
 }
 EXPORT_SYMBOL(jbd2_journal_put_journal_head);
 
 /*
  * Initialize jbd inode head
  */
 void jbd2_journal_init_jbd_inode(struct jbd2_inode *jinode, struct inode *inode)
 {
     jinode->i_transaction = NULL;
     jinode->i_next_transaction = NULL;
     jinode->i_vfs_inode = inode;
     jinode->i_flags = 0;
     jinode->i_dirty_start = 0;
     jinode->i_dirty_end = 0;
     INIT_LIST_HEAD(&jinode->i_list);
 }
 
 /*
  * Function to be called before we start removing inode from memory (i.e.,
  * clear_inode() is a fine place to be called from). It removes inode from
  * transaction's lists.
  */
 void jbd2_journal_release_jbd_inode(journal_t *journal,
                     struct jbd2_inode *jinode)
 {
     if (!journal)
         return;
 restart:
     spin_lock(&journal->j_list_lock);
     /* Is commit writing out inode - we have to wait */
     if (jinode->i_flags & JI_COMMIT_RUNNING) {
         wait_queue_head_t *wq;
         DEFINE_WAIT_BIT(wait, &jinode->i_flags, __JI_COMMIT_RUNNING);
         wq = bit_waitqueue(&jinode->i_flags, __JI_COMMIT_RUNNING);
         prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
         spin_unlock(&journal->j_list_lock);
         schedule();
         finish_wait(wq, &wait.wq_entry);
         goto restart;
     }
 
     if (jinode->i_transaction) {
         list_del(&jinode->i_list);
         jinode->i_transaction = NULL;
     }
     spin_unlock(&journal->j_list_lock);
 }
 
 
 #ifdef CONFIG_PROC_FS
 
 #define JBD2_STATS_PROC_NAME "fs/jbd2"
 
 static void __init jbd2_create_jbd_stats_proc_entry(void)
 {
     proc_jbd2_stats = proc_mkdir(JBD2_STATS_PROC_NAME, NULL);
 }
 
 static void __exit jbd2_remove_jbd_stats_proc_entry(void)
 {
     if (proc_jbd2_stats)
         remove_proc_entry(JBD2_STATS_PROC_NAME, NULL);
 }
 
 #else
 
 #define jbd2_create_jbd_stats_proc_entry() do {} while (0)
 #define jbd2_remove_jbd_stats_proc_entry() do {} while (0)
 
 #endif
 
 struct kmem_cache *jbd2_handle_cache, *jbd2_inode_cache;
 
 static int __init jbd2_journal_init_inode_cache(void)
 {
     J_ASSERT(!jbd2_inode_cache);
     jbd2_inode_cache = KMEM_CACHE(jbd2_inode, 0);
     if (!jbd2_inode_cache) {
         pr_emerg("JBD2: failed to create inode cache\n");
         return -ENOMEM;
     }
     return 0;
 }
 
 static int __init jbd2_journal_init_handle_cache(void)
 {
     J_ASSERT(!jbd2_handle_cache);
     jbd2_handle_cache = KMEM_CACHE(jbd2_journal_handle, SLAB_TEMPORARY);
     if (!jbd2_handle_cache) {
         printk(KERN_EMERG "JBD2: failed to create handle cache\n");
         return -ENOMEM;
     }
     return 0;
 }
 
 static void jbd2_journal_destroy_inode_cache(void)
 {
     kmem_cache_destroy(jbd2_inode_cache);
     jbd2_inode_cache = NULL;
 }
 
 static void jbd2_journal_destroy_handle_cache(void)
 {
     kmem_cache_destroy(jbd2_handle_cache);
     jbd2_handle_cache = NULL;
 }
 
 /*
  * Module startup and shutdown
  */
 
 static int __init journal_init_caches(void)
 {
     int ret;
 
     ret = jbd2_journal_init_revoke_record_cache();
     if (ret == 0)
         ret = jbd2_journal_init_revoke_table_cache();
     if (ret == 0)
         ret = jbd2_journal_init_journal_head_cache();
     if (ret == 0)
         ret = jbd2_journal_init_handle_cache();
     if (ret == 0)
         ret = jbd2_journal_init_inode_cache();
     if (ret == 0)
         ret = jbd2_journal_init_transaction_cache();
     return ret;
 }
 
 static void jbd2_journal_destroy_caches(void)
 {
     jbd2_journal_destroy_revoke_record_cache();
     jbd2_journal_destroy_revoke_table_cache();
     jbd2_journal_destroy_journal_head_cache();
     jbd2_journal_destroy_handle_cache();
     jbd2_journal_destroy_inode_cache();
     jbd2_journal_destroy_transaction_cache();
     jbd2_journal_destroy_slabs();
 }
 
 static int __init journal_init(void)
 {
     int ret;
 
     BUILD_BUG_ON(sizeof(struct journal_superblock_s) != 1024);
 
     ret = journal_init_caches();
     if (ret == 0) {
         jbd2_create_jbd_stats_proc_entry();
     } else {
         jbd2_journal_destroy_caches();
     }
     return ret;
 }
 
 static void __exit journal_exit(void)
 {
 #ifdef CONFIG_JBD2_DEBUG
     int n = atomic_read(&nr_journal_heads);
     if (n)
         printk(KERN_ERR "JBD2: leaked %d journal_heads!\n", n);
 #endif
     jbd2_remove_jbd_stats_proc_entry();
     jbd2_journal_destroy_caches();
 }
 
 MODULE_LICENSE("GPL");
 module_init(journal_init);
 module_exit(journal_exit);