text: /*
   * linux/fs/jbd2/transaction.c
   *
   * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
   *
   * Copyright 1998 Red Hat corp --- All Rights Reserved
   *
   * This file is part of the Linux kernel and is made available under
   * the terms of the GNU General Public License, version 2, or at your
   * option, any later version, incorporated herein by reference.
   *
   * Generic filesystem transaction handling code; part of the ext2fs
   * journaling system.
   *
   * This file manages transactions (compound commits managed by the
   * journaling code) and handles (individual atomic operations by the
   * filesystem).
   */
  
  #include <linux/time.h>
  #include <linux/fs.h>
  #include <linux/jbd2.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/timer.h>
  #include <linux/mm.h>
  #include <linux/highmem.h>
  #include <linux/hrtimer.h>
  #include <linux/backing-dev.h>
  #include <linux/bug.h>
  #include <linux/module.h>
  
  static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
  static void __jbd2_journal_unfile_buffer(struct journal_head *jh);
  
  /*
   * jbd2_get_transaction: obtain a new transaction_t object.
   *
   * Simply allocate and initialise a new transaction.  Create it in
   * RUNNING state and add it to the current journal (which should not
   * have an existing running transaction: we only make a new transaction
   * once we have started to commit the old one).
   *
   * Preconditions:
   *	The journal MUST be locked.  We don't perform atomic mallocs on the
   *	new transaction	and we can't block without protecting against other
   *	processes trying to touch the journal while it is in transition.
   *
   */
  
  static transaction_t *
  jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
  {
  	transaction->t_journal = journal;
  	transaction->t_state = T_RUNNING;
  	transaction->t_start_time = ktime_get();
  	transaction->t_tid = journal->j_transaction_sequence++;
  	transaction->t_expires = jiffies + journal->j_commit_interval;
  	spin_lock_init(&transaction->t_handle_lock);
  	atomic_set(&transaction->t_updates, 0);
  	atomic_set(&transaction->t_outstanding_credits, 0);
  	atomic_set(&transaction->t_handle_count, 0);
  	INIT_LIST_HEAD(&transaction->t_inode_list);
  	INIT_LIST_HEAD(&transaction->t_private_list);
  
  	/* Set up the commit timer for the new transaction. */
  	journal->j_commit_timer.expires = round_jiffies_up(transaction->t_expires);
  	add_timer(&journal->j_commit_timer);
  
  	J_ASSERT(journal->j_running_transaction == NULL);
  	journal->j_running_transaction = transaction;
  	transaction->t_max_wait = 0;
  	transaction->t_start = jiffies;
  
  	return transaction;
  }
  
  /*
   * Handle management.
   *
   * A handle_t is an object which represents a single atomic update to a
   * filesystem, and which tracks all of the modifications which form part
   * of that one update.
   */
  
  /*
   * Update transaction's maximum wait time, if debugging is enabled.
   *
   * In order for t_max_wait to be reliable, it must be protected by a
   * lock.  But doing so will mean that start_this_handle() can not be
   * run in parallel on SMP systems, which limits our scalability.  So
   * unless debugging is enabled, we no longer update t_max_wait, which
   * means that maximum wait time reported by the jbd2_run_stats
   * tracepoint will always be zero.
   */
  static inline void update_t_max_wait(transaction_t *transaction,
  				     unsigned long ts)
  {
  #ifdef CONFIG_JBD2_DEBUG
  	if (jbd2_journal_enable_debug &&
  	    time_after(transaction->t_start, ts)) {
  		ts = jbd2_time_diff(ts, transaction->t_start);
  		spin_lock(&transaction->t_handle_lock);
  		if (ts > transaction->t_max_wait)
  			transaction->t_max_wait = ts;
  		spin_unlock(&transaction->t_handle_lock);
  	}
  #endif
  }
  
  /*
   * start_this_handle: Given a handle, deal with any locking or stalling
   * needed to make sure that there is enough journal space for the handle
   * to begin.  Attach the handle to a transaction and set up the
   * transaction's buffer credits.
   */
  
  static int start_this_handle(journal_t *journal, handle_t *handle,
  			     gfp_t gfp_mask)
  {
  	transaction_t	*transaction, *new_transaction = NULL;
  	tid_t		tid;
  	int		needed, need_to_start;
  	int		nblocks = handle->h_buffer_credits;
  	unsigned long ts = jiffies;
  
  	if (nblocks > journal->j_max_transaction_buffers) {
  		printk(KERN_ERR "JBD2: %s wants too many credits (%d > %d)\n",
  		       current->comm, nblocks,
  		       journal->j_max_transaction_buffers);
  		return -ENOSPC;
  	}
  
  alloc_transaction:
  	if (!journal->j_running_transaction) {
  		new_transaction = kzalloc(sizeof(*new_transaction), gfp_mask);
  		if (!new_transaction) {
  			/*
  			 * If __GFP_FS is not present, then we may be
  			 * being called from inside the fs writeback
  			 * layer, so we MUST NOT fail.  Since
  			 * __GFP_NOFAIL is going away, we will arrange
  			 * to retry the allocation ourselves.
  			 */
  			if ((gfp_mask & __GFP_FS) == 0) {
  				congestion_wait(BLK_RW_ASYNC, HZ/50);
  				goto alloc_transaction;
  			}
  			return -ENOMEM;
  		}
  	}
  
  	jbd_debug(3, "New handle %p going live.\n", handle);
  
  	/*
  	 * We need to hold j_state_lock until t_updates has been incremented,
  	 * for proper journal barrier handling
  	 */
  repeat:
  	read_lock(&journal->j_state_lock);
  	BUG_ON(journal->j_flags & JBD2_UNMOUNT);
  	if (is_journal_aborted(journal) ||
  	    (journal->j_errno != 0 && !(journal->j_flags & JBD2_ACK_ERR))) {
  		read_unlock(&journal->j_state_lock);
  		kfree(new_transaction);
  		return -EROFS;
  	}
  
  	/* Wait on the journal's transaction barrier if necessary */
  	if (journal->j_barrier_count) {
  		read_unlock(&journal->j_state_lock);
  		wait_event(journal->j_wait_transaction_locked,
  				journal->j_barrier_count == 0);
  		goto repeat;
  	}
  
  	if (!journal->j_running_transaction) {
  		read_unlock(&journal->j_state_lock);
  		if (!new_transaction)
  			goto alloc_transaction;
  		write_lock(&journal->j_state_lock);
  		if (!journal->j_running_transaction) {
  			jbd2_get_transaction(journal, new_transaction);
  			new_transaction = NULL;
  		}
  		write_unlock(&journal->j_state_lock);
  		goto repeat;
  	}
  
  	transaction = journal->j_running_transaction;
  
  	/*
  	 * If the current transaction is locked down for commit, wait for the
  	 * lock to be released.
  	 */
  	if (transaction->t_state == T_LOCKED) {
  		DEFINE_WAIT(wait);
  
  		prepare_to_wait(&journal->j_wait_transaction_locked,
  					&wait, TASK_UNINTERRUPTIBLE);
  		read_unlock(&journal->j_state_lock);
  		schedule();
  		finish_wait(&journal->j_wait_transaction_locked, &wait);
  		goto repeat;
  	}
  
  	/*
  	 * If there is not enough space left in the log to write all potential
  	 * buffers requested by this operation, we need to stall pending a log
  	 * checkpoint to free some more log space.
  	 */
  	needed = atomic_add_return(nblocks,
  				   &transaction->t_outstanding_credits);
  
  	if (needed > journal->j_max_transaction_buffers) {
  		/*
  		 * If the current transaction is already too large, then start
  		 * to commit it: we can then go back and attach this handle to
  		 * a new transaction.
  		 */
  		DEFINE_WAIT(wait);
  
  		jbd_debug(2, "Handle %p starting new commit...\n", handle);
  		atomic_sub(nblocks, &transaction->t_outstanding_credits);
  		prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
  				TASK_UNINTERRUPTIBLE);
  		tid = transaction->t_tid;
  		need_to_start = !tid_geq(journal->j_commit_request, tid);
  		read_unlock(&journal->j_state_lock);
  		if (need_to_start)
  			jbd2_log_start_commit(journal, tid);
  		schedule();
  		finish_wait(&journal->j_wait_transaction_locked, &wait);
  		goto repeat;
  	}
  
  	/*
  	 * The commit code assumes that it can get enough log space
  	 * without forcing a checkpoint.  This is *critical* for
  	 * correctness: a checkpoint of a buffer which is also
  	 * associated with a committing transaction creates a deadlock,
  	 * so commit simply cannot force through checkpoints.
  	 *
  	 * We must therefore ensure the necessary space in the journal
  	 * *before* starting to dirty potentially checkpointed buffers
  	 * in the new transaction.
  	 *
  	 * The worst part is, any transaction currently committing can
  	 * reduce the free space arbitrarily.  Be careful to account for
  	 * those buffers when checkpointing.
  	 */
  
  	/*
  	 * @@@ AKPM: This seems rather over-defensive.  We're giving commit
  	 * a _lot_ of headroom: 1/4 of the journal plus the size of
  	 * the committing transaction.  Really, we only need to give it
  	 * committing_transaction->t_outstanding_credits plus "enough" for
  	 * the log control blocks.
  	 * Also, this test is inconsistent with the matching one in
  	 * jbd2_journal_extend().
  	 */
  	if (__jbd2_log_space_left(journal) < jbd_space_needed(journal)) {
  		jbd_debug(2, "Handle %p waiting for checkpoint...\n", handle);
  		atomic_sub(nblocks, &transaction->t_outstanding_credits);
  		read_unlock(&journal->j_state_lock);
  		write_lock(&journal->j_state_lock);
  		if (__jbd2_log_space_left(journal) < jbd_space_needed(journal))
  			__jbd2_log_wait_for_space(journal);
  		write_unlock(&journal->j_state_lock);
  		goto repeat;
  	}
  
  	/* OK, account for the buffers that this operation expects to
  	 * use and add the handle to the running transaction. 
  	 */
  	update_t_max_wait(transaction, ts);
  	handle->h_transaction = transaction;
  	atomic_inc(&transaction->t_updates);
  	atomic_inc(&transaction->t_handle_count);
  	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
  		  handle, nblocks,
  		  atomic_read(&transaction->t_outstanding_credits),
  		  __jbd2_log_space_left(journal));
  	read_unlock(&journal->j_state_lock);
  
  	lock_map_acquire(&handle->h_lockdep_map);
  	kfree(new_transaction);
  	return 0;
  }
  
  static struct lock_class_key jbd2_handle_key;
  
  /* Allocate a new handle.  This should probably be in a slab... */
  static handle_t *new_handle(int nblocks)
  {
  	handle_t *handle = jbd2_alloc_handle(GFP_NOFS);
  	if (!handle)
  		return NULL;
  	memset(handle, 0, sizeof(*handle));
  	handle->h_buffer_credits = nblocks;
  	handle->h_ref = 1;
  
  	lockdep_init_map(&handle->h_lockdep_map, "jbd2_handle",
  						&jbd2_handle_key, 0);
  
  	return handle;
  }
  
  /**
   * handle_t *jbd2_journal_start() - Obtain a new handle.
   * @journal: Journal to start transaction on.
   * @nblocks: number of block buffer we might modify
   *
   * We make sure that the transaction can guarantee at least nblocks of
   * modified buffers in the log.  We block until the log can guarantee
   * that much space.
   *
   * This function is visible to journal users (like ext3fs), so is not
   * called with the journal already locked.
   *
   * Return a pointer to a newly allocated handle, or an ERR_PTR() value
   * on failure.
   */
  handle_t *jbd2__journal_start(journal_t *journal, int nblocks, gfp_t gfp_mask)
  {
  	handle_t *handle = journal_current_handle();
  	int err;
  
  	if (!journal)
  		return ERR_PTR(-EROFS);
  
  	if (handle) {
  		J_ASSERT(handle->h_transaction->t_journal == journal);
  		handle->h_ref++;
  		return handle;
  	}
  
  	handle = new_handle(nblocks);
  	if (!handle)
  		return ERR_PTR(-ENOMEM);
  
  	current->journal_info = handle;
  
  	err = start_this_handle(journal, handle, gfp_mask);
  	if (err < 0) {
  		jbd2_free_handle(handle);
  		current->journal_info = NULL;
  		handle = ERR_PTR(err);
  	}
  	return handle;
  }
  EXPORT_SYMBOL(jbd2__journal_start);
  
  
  handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
  {
  	return jbd2__journal_start(journal, nblocks, GFP_NOFS);
  }
  EXPORT_SYMBOL(jbd2_journal_start);
  
  
  /**
   * int jbd2_journal_extend() - extend buffer credits.
   * @handle:  handle to 'extend'
   * @nblocks: nr blocks to try to extend by.
   *
   * Some transactions, such as large extends and truncates, can be done
   * atomically all at once or in several stages.  The operation requests
   * a credit for a number of buffer modications in advance, but can
   * extend its credit if it needs more.
   *
   * jbd2_journal_extend tries to give the running handle more buffer credits.
   * It does not guarantee that allocation - this is a best-effort only.
   * The calling process MUST be able to deal cleanly with a failure to
   * extend here.
   *
   * Return 0 on success, non-zero on failure.
   *
   * return code < 0 implies an error
   * return code > 0 implies normal transaction-full status.
   */
  int jbd2_journal_extend(handle_t *handle, int nblocks)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	int result;
  	int wanted;
  
  	result = -EIO;
  	if (is_handle_aborted(handle))
  		goto out;
  
  	result = 1;
  
  	read_lock(&journal->j_state_lock);
  
  	/* Don't extend a locked-down transaction! */
  	if (handle->h_transaction->t_state != T_RUNNING) {
  		jbd_debug(3, "denied handle %p %d blocks: "
  			  "transaction not running\n", handle, nblocks);
  		goto error_out;
  	}
  
  	spin_lock(&transaction->t_handle_lock);
  	wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
  
  	if (wanted > journal->j_max_transaction_buffers) {
  		jbd_debug(3, "denied handle %p %d blocks: "
  			  "transaction too large\n", handle, nblocks);
  		goto unlock;
  	}
  
  	if (wanted > __jbd2_log_space_left(journal)) {
  		jbd_debug(3, "denied handle %p %d blocks: "
  			  "insufficient log space\n", handle, nblocks);
  		goto unlock;
  	}
  
  	handle->h_buffer_credits += nblocks;
  	atomic_add(nblocks, &transaction->t_outstanding_credits);
  	result = 0;
  
  	jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
  unlock:
  	spin_unlock(&transaction->t_handle_lock);
  error_out:
  	read_unlock(&journal->j_state_lock);
  out:
  	return result;
  }
  
  
  /**
   * int jbd2_journal_restart() - restart a handle .
   * @handle:  handle to restart
   * @nblocks: nr credits requested
   *
   * Restart a handle for a multi-transaction filesystem
   * operation.
   *
   * If the jbd2_journal_extend() call above fails to grant new buffer credits
   * to a running handle, a call to jbd2_journal_restart will commit the
   * handle's transaction so far and reattach the handle to a new
   * transaction capabable of guaranteeing the requested number of
   * credits.
   */
  int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	tid_t		tid;
  	int		need_to_start, ret;
  
  	/* If we've had an abort of any type, don't even think about
  	 * actually doing the restart! */
  	if (is_handle_aborted(handle))
  		return 0;
  
  	/*
  	 * First unlink the handle from its current transaction, and start the
  	 * commit on that.
  	 */
  	J_ASSERT(atomic_read(&transaction->t_updates) > 0);
  	J_ASSERT(journal_current_handle() == handle);
  
  	read_lock(&journal->j_state_lock);
  	spin_lock(&transaction->t_handle_lock);
  	atomic_sub(handle->h_buffer_credits,
  		   &transaction->t_outstanding_credits);
  	if (atomic_dec_and_test(&transaction->t_updates))
  		wake_up(&journal->j_wait_updates);
  	spin_unlock(&transaction->t_handle_lock);
  
  	jbd_debug(2, "restarting handle %p\n", handle);
  	tid = transaction->t_tid;
  	need_to_start = !tid_geq(journal->j_commit_request, tid);
  	read_unlock(&journal->j_state_lock);
  	if (need_to_start)
  		jbd2_log_start_commit(journal, tid);
  
  	lock_map_release(&handle->h_lockdep_map);
  	handle->h_buffer_credits = nblocks;
  	ret = start_this_handle(journal, handle, gfp_mask);
  	return ret;
  }
  EXPORT_SYMBOL(jbd2__journal_restart);
  
  
  int jbd2_journal_restart(handle_t *handle, int nblocks)
  {
  	return jbd2__journal_restart(handle, nblocks, GFP_NOFS);
  }
  EXPORT_SYMBOL(jbd2_journal_restart);
  
  /**
   * void jbd2_journal_lock_updates () - establish a transaction barrier.
   * @journal:  Journal to establish a barrier on.
   *
   * This locks out any further updates from being started, and blocks
   * until all existing updates have completed, returning only once the
   * journal is in a quiescent state with no updates running.
   *
   * The journal lock should not be held on entry.
   */
  void jbd2_journal_lock_updates(journal_t *journal)
  {
  	DEFINE_WAIT(wait);
  
  	write_lock(&journal->j_state_lock);
  	++journal->j_barrier_count;
  
  	/* Wait until there are no running updates */
  	while (1) {
  		transaction_t *transaction = journal->j_running_transaction;
  
  		if (!transaction)
  			break;
  
  		spin_lock(&transaction->t_handle_lock);
  		prepare_to_wait(&journal->j_wait_updates, &wait,
  				TASK_UNINTERRUPTIBLE);
  		if (!atomic_read(&transaction->t_updates)) {
  			spin_unlock(&transaction->t_handle_lock);
  			finish_wait(&journal->j_wait_updates, &wait);
  			break;
  		}
  		spin_unlock(&transaction->t_handle_lock);
  		write_unlock(&journal->j_state_lock);
  		schedule();
  		finish_wait(&journal->j_wait_updates, &wait);
  		write_lock(&journal->j_state_lock);
  	}
  	write_unlock(&journal->j_state_lock);
  
  	/*
  	 * We have now established a barrier against other normal updates, but
  	 * we also need to barrier against other jbd2_journal_lock_updates() calls
  	 * to make sure that we serialise special journal-locked operations
  	 * too.
  	 */
  	mutex_lock(&journal->j_barrier);
  }
  
  /**
   * void jbd2_journal_unlock_updates (journal_t* journal) - release barrier
   * @journal:  Journal to release the barrier on.
   *
   * Release a transaction barrier obtained with jbd2_journal_lock_updates().
   *
   * Should be called without the journal lock held.
   */
  void jbd2_journal_unlock_updates (journal_t *journal)
  {
  	J_ASSERT(journal->j_barrier_count != 0);
  
  	mutex_unlock(&journal->j_barrier);
  	write_lock(&journal->j_state_lock);
  	--journal->j_barrier_count;
  	write_unlock(&journal->j_state_lock);
  	wake_up(&journal->j_wait_transaction_locked);
  }
  
  static void warn_dirty_buffer(struct buffer_head *bh)
  {
  	char b[BDEVNAME_SIZE];
  
  	printk(KERN_WARNING
  	       "JBD2: Spotted dirty metadata buffer (dev = %s, blocknr = %llu). "
  	       "There's a risk of filesystem corruption in case of system "
  	       "crash.\n",
  	       bdevname(bh->b_bdev, b), (unsigned long long)bh->b_blocknr);
  }
  
  /*
   * If the buffer is already part of the current transaction, then there
   * is nothing we need to do.  If it is already part of a prior
   * transaction which we are still committing to disk, then we need to
   * make sure that we do not overwrite the old copy: we do copy-out to
   * preserve the copy going to disk.  We also account the buffer against
   * the handle's metadata buffer credits (unless the buffer is already
   * part of the transaction, that is).
   *
   */
  static int
  do_get_write_access(handle_t *handle, struct journal_head *jh,
  			int force_copy)
  {
  	struct buffer_head *bh;
  	transaction_t *transaction;
  	journal_t *journal;
  	int error;
  	char *frozen_buffer = NULL;
  	int need_copy = 0;
  
  	if (is_handle_aborted(handle))
  		return -EROFS;
  
  	transaction = handle->h_transaction;
  	journal = transaction->t_journal;
  
  	jbd_debug(5, "journal_head %p, force_copy %d\n", jh, force_copy);
  
  	JBUFFER_TRACE(jh, "entry");
  repeat:
  	bh = jh2bh(jh);
  
  	/* @@@ Need to check for errors here at some point. */
  
  	lock_buffer(bh);
  	jbd_lock_bh_state(bh);
  
  	/* We now hold the buffer lock so it is safe to query the buffer
  	 * state.  Is the buffer dirty?
  	 *
  	 * If so, there are two possibilities.  The buffer may be
  	 * non-journaled, and undergoing a quite legitimate writeback.
  	 * Otherwise, it is journaled, and we don't expect dirty buffers
  	 * in that state (the buffers should be marked JBD_Dirty
  	 * instead.)  So either the IO is being done under our own
  	 * control and this is a bug, or it's a third party IO such as
  	 * dump(8) (which may leave the buffer scheduled for read ---
  	 * ie. locked but not dirty) or tune2fs (which may actually have
  	 * the buffer dirtied, ugh.)  */
  
  	if (buffer_dirty(bh)) {
  		/*
  		 * First question: is this buffer already part of the current
  		 * transaction or the existing committing transaction?
  		 */
  		if (jh->b_transaction) {
  			J_ASSERT_JH(jh,
  				jh->b_transaction == transaction ||
  				jh->b_transaction ==
  					journal->j_committing_transaction);
  			if (jh->b_next_transaction)
  				J_ASSERT_JH(jh, jh->b_next_transaction ==
  							transaction);
  			warn_dirty_buffer(bh);
  		}
  		/*
  		 * In any case we need to clean the dirty flag and we must
  		 * do it under the buffer lock to be sure we don't race
  		 * with running write-out.
  		 */
  		JBUFFER_TRACE(jh, "Journalling dirty buffer");
  		clear_buffer_dirty(bh);
  		set_buffer_jbddirty(bh);
  	}
  
  	unlock_buffer(bh);
  
  	error = -EROFS;
  	if (is_handle_aborted(handle)) {
  		jbd_unlock_bh_state(bh);
  		goto out;
  	}
  	error = 0;
  
  	/*
  	 * The buffer is already part of this transaction if b_transaction or
  	 * b_next_transaction points to it
  	 */
  	if (jh->b_transaction == transaction ||
  	    jh->b_next_transaction == transaction)
  		goto done;
  
  	/*
  	 * this is the first time this transaction is touching this buffer,
  	 * reset the modified flag
  	 */
         jh->b_modified = 0;
  
  	/*
  	 * If there is already a copy-out version of this buffer, then we don't
  	 * need to make another one
  	 */
  	if (jh->b_frozen_data) {
  		JBUFFER_TRACE(jh, "has frozen data");
  		J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
  		jh->b_next_transaction = transaction;
  		goto done;
  	}
  
  	/* Is there data here we need to preserve? */
  
  	if (jh->b_transaction && jh->b_transaction != transaction) {
  		JBUFFER_TRACE(jh, "owned by older transaction");
  		J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
  		J_ASSERT_JH(jh, jh->b_transaction ==
  					journal->j_committing_transaction);
  
  		/* There is one case we have to be very careful about.
  		 * If the committing transaction is currently writing
  		 * this buffer out to disk and has NOT made a copy-out,
  		 * then we cannot modify the buffer contents at all
  		 * right now.  The essence of copy-out is that it is the
  		 * extra copy, not the primary copy, which gets
  		 * journaled.  If the primary copy is already going to
  		 * disk then we cannot do copy-out here. */
  
  		if (jh->b_jlist == BJ_Shadow) {
  			DEFINE_WAIT_BIT(wait, &bh->b_state, BH_Unshadow);
  			wait_queue_head_t *wqh;
  
  			wqh = bit_waitqueue(&bh->b_state, BH_Unshadow);
  
  			JBUFFER_TRACE(jh, "on shadow: sleep");
  			jbd_unlock_bh_state(bh);
  			/* commit wakes up all shadow buffers after IO */
  			for ( ; ; ) {
  				prepare_to_wait(wqh, &wait.wait,
  						TASK_UNINTERRUPTIBLE);
  				if (jh->b_jlist != BJ_Shadow)
  					break;
  				schedule();
  			}
  			finish_wait(wqh, &wait.wait);
  			goto repeat;
  		}
  
  		/* Only do the copy if the currently-owning transaction
  		 * still needs it.  If it is on the Forget list, the
  		 * committing transaction is past that stage.  The
  		 * buffer had better remain locked during the kmalloc,
  		 * but that should be true --- we hold the journal lock
  		 * still and the buffer is already on the BUF_JOURNAL
  		 * list so won't be flushed.
  		 *
  		 * Subtle point, though: if this is a get_undo_access,
  		 * then we will be relying on the frozen_data to contain
  		 * the new value of the committed_data record after the
  		 * transaction, so we HAVE to force the frozen_data copy
  		 * in that case. */
  
  		if (jh->b_jlist != BJ_Forget || force_copy) {
  			JBUFFER_TRACE(jh, "generate frozen data");
  			if (!frozen_buffer) {
  				JBUFFER_TRACE(jh, "allocate memory for buffer");
  				jbd_unlock_bh_state(bh);
  				frozen_buffer =
  					jbd2_alloc(jh2bh(jh)->b_size,
  							 GFP_NOFS);
  				if (!frozen_buffer) {
  					printk(KERN_EMERG
  					       "%s: OOM for frozen_buffer\n",
  					       __func__);
  					JBUFFER_TRACE(jh, "oom!");
  					error = -ENOMEM;
  					jbd_lock_bh_state(bh);
  					goto done;
  				}
  				goto repeat;
  			}
  			jh->b_frozen_data = frozen_buffer;
  			frozen_buffer = NULL;
  			need_copy = 1;
  		}
  		jh->b_next_transaction = transaction;
  	}
  
  
  	/*
  	 * Finally, if the buffer is not journaled right now, we need to make
  	 * sure it doesn't get written to disk before the caller actually
  	 * commits the new data
  	 */
  	if (!jh->b_transaction) {
  		JBUFFER_TRACE(jh, "no transaction");
  		J_ASSERT_JH(jh, !jh->b_next_transaction);
  		JBUFFER_TRACE(jh, "file as BJ_Reserved");
  		spin_lock(&journal->j_list_lock);
  		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
  		spin_unlock(&journal->j_list_lock);
  	}
  
  done:
  	if (need_copy) {
  		struct page *page;
  		int offset;
  		char *source;
  
  		J_EXPECT_JH(jh, buffer_uptodate(jh2bh(jh)),
  			    "Possible IO failure.\n");
  		page = jh2bh(jh)->b_page;
  		offset = offset_in_page(jh2bh(jh)->b_data);
  		source = kmap_atomic(page, KM_USER0);
  		/* Fire data frozen trigger just before we copy the data */
  		jbd2_buffer_frozen_trigger(jh, source + offset,
  					   jh->b_triggers);
  		memcpy(jh->b_frozen_data, source+offset, jh2bh(jh)->b_size);
  		kunmap_atomic(source, KM_USER0);
  
  		/*
  		 * Now that the frozen data is saved off, we need to store
  		 * any matching triggers.
  		 */
  		jh->b_frozen_triggers = jh->b_triggers;
  	}
  	jbd_unlock_bh_state(bh);
  
  	/*
  	 * If we are about to journal a buffer, then any revoke pending on it is
  	 * no longer valid
  	 */
  	jbd2_journal_cancel_revoke(handle, jh);
  
  out:
  	if (unlikely(frozen_buffer))	/* It's usually NULL */
  		jbd2_free(frozen_buffer, bh->b_size);
  
  	JBUFFER_TRACE(jh, "exit");
  	return error;
  }
  
  /**
   * int jbd2_journal_get_write_access() - notify intent to modify a buffer for metadata (not data) update.
   * @handle: transaction to add buffer modifications to
   * @bh:     bh to be used for metadata writes
   *
   * Returns an error code or 0 on success.
   *
   * In full data journalling mode the buffer may be of type BJ_AsyncData,
   * because we're write()ing a buffer which is also part of a shared mapping.
   */
  
  int jbd2_journal_get_write_access(handle_t *handle, struct buffer_head *bh)
  {
  	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
  	int rc;
  
  	/* We do not want to get caught playing with fields which the
  	 * log thread also manipulates.  Make sure that the buffer
  	 * completes any outstanding IO before proceeding. */
  	rc = do_get_write_access(handle, jh, 0);
  	jbd2_journal_put_journal_head(jh);
  	return rc;
  }
  
  
  /*
   * When the user wants to journal a newly created buffer_head
   * (ie. getblk() returned a new buffer and we are going to populate it
   * manually rather than reading off disk), then we need to keep the
   * buffer_head locked until it has been completely filled with new
   * data.  In this case, we should be able to make the assertion that
   * the bh is not already part of an existing transaction.
   *
   * The buffer should already be locked by the caller by this point.
   * There is no lock ranking violation: it was a newly created,
   * unlocked buffer beforehand. */
  
  /**
   * int jbd2_journal_get_create_access () - notify intent to use newly created bh
   * @handle: transaction to new buffer to
   * @bh: new buffer.
   *
   * Call this if you create a new bh.
   */
  int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
  	int err;
  
  	jbd_debug(5, "journal_head %p\n", jh);
  	err = -EROFS;
  	if (is_handle_aborted(handle))
  		goto out;
  	err = 0;
  
  	JBUFFER_TRACE(jh, "entry");
  	/*
  	 * The buffer may already belong to this transaction due to pre-zeroing
  	 * in the filesystem's new_block code.  It may also be on the previous,
  	 * committing transaction's lists, but it HAS to be in Forget state in
  	 * that case: the transaction must have deleted the buffer for it to be
  	 * reused here.
  	 */
  	jbd_lock_bh_state(bh);
  	spin_lock(&journal->j_list_lock);
  	J_ASSERT_JH(jh, (jh->b_transaction == transaction ||
  		jh->b_transaction == NULL ||
  		(jh->b_transaction == journal->j_committing_transaction &&
  			  jh->b_jlist == BJ_Forget)));
  
  	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
  	J_ASSERT_JH(jh, buffer_locked(jh2bh(jh)));
  
  	if (jh->b_transaction == NULL) {
  		/*
  		 * Previous jbd2_journal_forget() could have left the buffer
  		 * with jbddirty bit set because it was being committed. When
  		 * the commit finished, we've filed the buffer for
  		 * checkpointing and marked it dirty. Now we are reallocating
  		 * the buffer so the transaction freeing it must have
  		 * committed and so it's safe to clear the dirty bit.
  		 */
  		clear_buffer_dirty(jh2bh(jh));
  		/* first access by this transaction */
  		jh->b_modified = 0;
  
  		JBUFFER_TRACE(jh, "file as BJ_Reserved");
  		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
  	} else if (jh->b_transaction == journal->j_committing_transaction) {
  		/* first access by this transaction */
  		jh->b_modified = 0;
  
  		JBUFFER_TRACE(jh, "set next transaction");
  		jh->b_next_transaction = transaction;
  	}
  	spin_unlock(&journal->j_list_lock);
  	jbd_unlock_bh_state(bh);
  
  	/*
  	 * akpm: I added this.  ext3_alloc_branch can pick up new indirect
  	 * blocks which contain freed but then revoked metadata.  We need
  	 * to cancel the revoke in case we end up freeing it yet again
  	 * and the reallocating as data - this would cause a second revoke,
  	 * which hits an assertion error.
  	 */
  	JBUFFER_TRACE(jh, "cancelling revoke");
  	jbd2_journal_cancel_revoke(handle, jh);
  out:
  	jbd2_journal_put_journal_head(jh);
  	return err;
  }
  
  /**
   * int jbd2_journal_get_undo_access() -  Notify intent to modify metadata with
   *     non-rewindable consequences
   * @handle: transaction
   * @bh: buffer to undo
   *
   * Sometimes there is a need to distinguish between metadata which has
   * been committed to disk and that which has not.  The ext3fs code uses
   * this for freeing and allocating space, we have to make sure that we
   * do not reuse freed space until the deallocation has been committed,
   * since if we overwrote that space we would make the delete
   * un-rewindable in case of a crash.
   *
   * To deal with that, jbd2_journal_get_undo_access requests write access to a
   * buffer for parts of non-rewindable operations such as delete
   * operations on the bitmaps.  The journaling code must keep a copy of
   * the buffer's contents prior to the undo_access call until such time
   * as we know that the buffer has definitely been committed to disk.
   *
   * We never need to know which transaction the committed data is part
   * of, buffers touched here are guaranteed to be dirtied later and so
   * will be committed to a new transaction in due course, at which point
   * we can discard the old committed data pointer.
   *
   * Returns error number or 0 on success.
   */
  int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
  {
  	int err;
  	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
  	char *committed_data = NULL;
  
  	JBUFFER_TRACE(jh, "entry");
  
  	/*
  	 * Do this first --- it can drop the journal lock, so we want to
  	 * make sure that obtaining the committed_data is done
  	 * atomically wrt. completion of any outstanding commits.
  	 */
  	err = do_get_write_access(handle, jh, 1);
  	if (err)
  		goto out;
  
  repeat:
  	if (!jh->b_committed_data) {
  		committed_data = jbd2_alloc(jh2bh(jh)->b_size, GFP_NOFS);
  		if (!committed_data) {
  			printk(KERN_EMERG "%s: No memory for committed data\n",
  				__func__);
  			err = -ENOMEM;
  			goto out;
  		}
  	}
  
  	jbd_lock_bh_state(bh);
  	if (!jh->b_committed_data) {
  		/* Copy out the current buffer contents into the
  		 * preserved, committed copy. */
  		JBUFFER_TRACE(jh, "generate b_committed data");
  		if (!committed_data) {
  			jbd_unlock_bh_state(bh);
  			goto repeat;
  		}
  
  		jh->b_committed_data = committed_data;
  		committed_data = NULL;
  		memcpy(jh->b_committed_data, bh->b_data, bh->b_size);
  	}
  	jbd_unlock_bh_state(bh);
  out:
  	jbd2_journal_put_journal_head(jh);
  	if (unlikely(committed_data))
  		jbd2_free(committed_data, bh->b_size);
  	return err;
  }
  
  /**
   * void jbd2_journal_set_triggers() - Add triggers for commit writeout
   * @bh: buffer to trigger on
   * @type: struct jbd2_buffer_trigger_type containing the trigger(s).
   *
   * Set any triggers on this journal_head.  This is always safe, because
   * triggers for a committing buffer will be saved off, and triggers for
   * a running transaction will match the buffer in that transaction.
   *
   * Call with NULL to clear the triggers.
   */
  void jbd2_journal_set_triggers(struct buffer_head *bh,
  			       struct jbd2_buffer_trigger_type *type)
  {
  	struct journal_head *jh = bh2jh(bh);
  
  	jh->b_triggers = type;
  }
  
  void jbd2_buffer_frozen_trigger(struct journal_head *jh, void *mapped_data,
  				struct jbd2_buffer_trigger_type *triggers)
  {
  	struct buffer_head *bh = jh2bh(jh);
  
  	if (!triggers || !triggers->t_frozen)
  		return;
  
  	triggers->t_frozen(triggers, bh, mapped_data, bh->b_size);
  }
  
  void jbd2_buffer_abort_trigger(struct journal_head *jh,
  			       struct jbd2_buffer_trigger_type *triggers)
  {
  	if (!triggers || !triggers->t_abort)
  		return;
  
  	triggers->t_abort(triggers, jh2bh(jh));
  }
  
  
  
  /**
   * int jbd2_journal_dirty_metadata() -  mark a buffer as containing dirty metadata
   * @handle: transaction to add buffer to.
   * @bh: buffer to mark
   *
   * mark dirty metadata which needs to be journaled as part of the current
   * transaction.
   *
   * The buffer must have previously had jbd2_journal_get_write_access()
   * called so that it has a valid journal_head attached to the buffer
   * head.
   *
   * The buffer is placed on the transaction's metadata list and is marked
   * as belonging to the transaction.
   *
   * Returns error number or 0 on success.
   *
   * Special care needs to be taken if the buffer already belongs to the
   * current committing transaction (in which case we should have frozen
   * data present for that commit).  In that case, we don't relink the
   * buffer: that only gets done when the old transaction finally
   * completes its commit.
   */
  int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	struct journal_head *jh = bh2jh(bh);
  	int ret = 0;
  
  	jbd_debug(5, "journal_head %p\n", jh);
  	JBUFFER_TRACE(jh, "entry");
  	if (is_handle_aborted(handle))
  		goto out;
  	if (!buffer_jbd(bh)) {
  		ret = -EUCLEAN;
  		goto out;
  	}
  
  	jbd_lock_bh_state(bh);
  
  	if (jh->b_modified == 0) {
  		/*
  		 * This buffer's got modified and becoming part
  		 * of the transaction. This needs to be done
  		 * once a transaction -bzzz
  		 */
  		jh->b_modified = 1;
  		J_ASSERT_JH(jh, handle->h_buffer_credits > 0);
  		handle->h_buffer_credits--;
  	}
  
  	/*
  	 * fastpath, to avoid expensive locking.  If this buffer is already
  	 * on the running transaction's metadata list there is nothing to do.
  	 * Nobody can take it off again because there is a handle open.
  	 * I _think_ we're OK here with SMP barriers - a mistaken decision will
  	 * result in this test being false, so we go in and take the locks.
  	 */
  	if (jh->b_transaction == transaction && jh->b_jlist == BJ_Metadata) {
  		JBUFFER_TRACE(jh, "fastpath");
  		if (unlikely(jh->b_transaction !=
  			     journal->j_running_transaction)) {
  			printk(KERN_EMERG "JBD: %s: "
  			       "jh->b_transaction (%llu, %p, %u) != "
  			       "journal->j_running_transaction (%p, %u)",
  			       journal->j_devname,
  			       (unsigned long long) bh->b_blocknr,
  			       jh->b_transaction,
  			       jh->b_transaction ? jh->b_transaction->t_tid : 0,
  			       journal->j_running_transaction,
  			       journal->j_running_transaction ?
  			       journal->j_running_transaction->t_tid : 0);
  			ret = -EINVAL;
  		}
  		goto out_unlock_bh;
  	}
  
  	set_buffer_jbddirty(bh);
  
  	/*
  	 * Metadata already on the current transaction list doesn't
  	 * need to be filed.  Metadata on another transaction's list must
  	 * be committing, and will be refiled once the commit completes:
  	 * leave it alone for now.
  	 */
  	if (jh->b_transaction != transaction) {
  		JBUFFER_TRACE(jh, "already on other transaction");
  		if (unlikely(jh->b_transaction !=
  			     journal->j_committing_transaction)) {
  			printk(KERN_EMERG "JBD: %s: "
  			       "jh->b_transaction (%llu, %p, %u) != "
  			       "journal->j_committing_transaction (%p, %u)",
  			       journal->j_devname,
  			       (unsigned long long) bh->b_blocknr,
  			       jh->b_transaction,
  			       jh->b_transaction ? jh->b_transaction->t_tid : 0,
  			       journal->j_committing_transaction,
  			       journal->j_committing_transaction ?
  			       journal->j_committing_transaction->t_tid : 0);
  			ret = -EINVAL;
  		}
  		if (unlikely(jh->b_next_transaction != transaction)) {
  			printk(KERN_EMERG "JBD: %s: "
  			       "jh->b_next_transaction (%llu, %p, %u) != "
  			       "transaction (%p, %u)",
  			       journal->j_devname,
  			       (unsigned long long) bh->b_blocknr,
  			       jh->b_next_transaction,
  			       jh->b_next_transaction ?
  			       jh->b_next_transaction->t_tid : 0,
  			       transaction, transaction->t_tid);
  			ret = -EINVAL;
  		}
  		/* And this case is illegal: we can't reuse another
  		 * transaction's data buffer, ever. */
  		goto out_unlock_bh;
  	}
  
  	/* That test should have eliminated the following case: */
  	J_ASSERT_JH(jh, jh->b_frozen_data == NULL);
  
  	JBUFFER_TRACE(jh, "file as BJ_Metadata");
  	spin_lock(&journal->j_list_lock);
  	__jbd2_journal_file_buffer(jh, handle->h_transaction, BJ_Metadata);
  	spin_unlock(&journal->j_list_lock);
  out_unlock_bh:
  	jbd_unlock_bh_state(bh);
  out:
  	JBUFFER_TRACE(jh, "exit");
  	WARN_ON(ret);	/* All errors are bugs, so dump the stack */
  	return ret;
  }
  
  /*
   * jbd2_journal_release_buffer: undo a get_write_access without any buffer
   * updates, if the update decided in the end that it didn't need access.
   *
   */
  void
  jbd2_journal_release_buffer(handle_t *handle, struct buffer_head *bh)
  {
  	BUFFER_TRACE(bh, "entry");
  }
  
  /**
   * void jbd2_journal_forget() - bforget() for potentially-journaled buffers.
   * @handle: transaction handle
   * @bh:     bh to 'forget'
   *
   * We can only do the bforget if there are no commits pending against the
   * buffer.  If the buffer is dirty in the current running transaction we
   * can safely unlink it.
   *
   * bh may not be a journalled buffer at all - it may be a non-JBD
   * buffer which came off the hashtable.  Check for this.
   *
   * Decrements bh->b_count by one.
   *
   * Allow this call even if the handle has aborted --- it may be part of
   * the caller's cleanup after an abort.
   */
  int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	struct journal_head *jh;
  	int drop_reserve = 0;
  	int err = 0;
  	int was_modified = 0;
  
  	BUFFER_TRACE(bh, "entry");
  
  	jbd_lock_bh_state(bh);
  	spin_lock(&journal->j_list_lock);
  
  	if (!buffer_jbd(bh))
  		goto not_jbd;
  	jh = bh2jh(bh);
  
  	/* Critical error: attempting to delete a bitmap buffer, maybe?
  	 * Don't do any jbd operations, and return an error. */
  	if (!J_EXPECT_JH(jh, !jh->b_committed_data,
  			 "inconsistent data on disk")) {
  		err = -EIO;
  		goto not_jbd;
  	}
  
  	/* keep track of wether or not this transaction modified us */
  	was_modified = jh->b_modified;
  
  	/*
  	 * The buffer's going from the transaction, we must drop
  	 * all references -bzzz
  	 */
  	jh->b_modified = 0;
  
  	if (jh->b_transaction == handle->h_transaction) {
  		J_ASSERT_JH(jh, !jh->b_frozen_data);
  
  		/* If we are forgetting a buffer which is already part
  		 * of this transaction, then we can just drop it from
  		 * the transaction immediately. */
  		clear_buffer_dirty(bh);
  		clear_buffer_jbddirty(bh);
  
  		JBUFFER_TRACE(jh, "belongs to current transaction: unfile");
  
  		/*
  		 * we only want to drop a reference if this transaction
  		 * modified the buffer
  		 */
  		if (was_modified)
  			drop_reserve = 1;
  
  		/*
  		 * We are no longer going to journal this buffer.
  		 * However, the commit of this transaction is still
  		 * important to the buffer: the delete that we are now
  		 * processing might obsolete an old log entry, so by
  		 * committing, we can satisfy the buffer's checkpoint.
  		 *
  		 * So, if we have a checkpoint on the buffer, we should
  		 * now refile the buffer on our BJ_Forget list so that
  		 * we know to remove the checkpoint after we commit.
  		 */
  
  		if (jh->b_cp_transaction) {
  			__jbd2_journal_temp_unlink_buffer(jh);
  			__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
  		} else {
  			__jbd2_journal_unfile_buffer(jh);
  			if (!buffer_jbd(bh)) {
  				spin_unlock(&journal->j_list_lock);
  				jbd_unlock_bh_state(bh);
  				__bforget(bh);
  				goto drop;
  			}
  		}
  	} else if (jh->b_transaction) {
  		J_ASSERT_JH(jh, (jh->b_transaction ==
  				 journal->j_committing_transaction));
  		/* However, if the buffer is still owned by a prior
  		 * (committing) transaction, we can't drop it yet... */
  		JBUFFER_TRACE(jh, "belongs to older transaction");
  		/* ... but we CAN drop it from the new transaction if we
  		 * have also modified it since the original commit. */
  
  		if (jh->b_next_transaction) {
  			J_ASSERT(jh->b_next_transaction == transaction);
  			jh->b_next_transaction = NULL;
  
  			/*
  			 * only drop a reference if this transaction modified
  			 * the buffer
  			 */
  			if (was_modified)
  				drop_reserve = 1;
  		}
  	}
  
  not_jbd:
  	spin_unlock(&journal->j_list_lock);
  	jbd_unlock_bh_state(bh);
  	__brelse(bh);
  drop:
  	if (drop_reserve) {
  		/* no need to reserve log space for this block -bzzz */
  		handle->h_buffer_credits++;
  	}
  	return err;
  }
  
  /**
   * int jbd2_journal_stop() - complete a transaction
   * @handle: tranaction to complete.
   *
   * All done for a particular handle.
   *
   * There is not much action needed here.  We just return any remaining
   * buffer credits to the transaction and remove the handle.  The only
   * complication is that we need to start a commit operation if the
   * filesystem is marked for synchronous update.
   *
   * jbd2_journal_stop itself will not usually return an error, but it may
   * do so in unusual circumstances.  In particular, expect it to
   * return -EIO if a jbd2_journal_abort has been executed since the
   * transaction began.
   */
  int jbd2_journal_stop(handle_t *handle)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  	int err, wait_for_commit = 0;
  	tid_t tid;
  	pid_t pid;
  
  	J_ASSERT(journal_current_handle() == handle);
  
  	if (is_handle_aborted(handle))
  		err = -EIO;
  	else {
  		J_ASSERT(atomic_read(&transaction->t_updates) > 0);
  		err = 0;
  	}
  
  	if (--handle->h_ref > 0) {
  		jbd_debug(4, "h_ref %d -> %d\n", handle->h_ref + 1,
  			  handle->h_ref);
  		return err;
  	}
  
  	jbd_debug(4, "Handle %p going down\n", handle);
  
  	/*
  	 * Implement synchronous transaction batching.  If the handle
  	 * was synchronous, don't force a commit immediately.  Let's
  	 * yield and let another thread piggyback onto this
  	 * transaction.  Keep doing that while new threads continue to
  	 * arrive.  It doesn't cost much - we're about to run a commit
  	 * and sleep on IO anyway.  Speeds up many-threaded, many-dir
  	 * operations by 30x or more...
  	 *
  	 * We try and optimize the sleep time against what the
  	 * underlying disk can do, instead of having a static sleep
  	 * time.  This is useful for the case where our storage is so
  	 * fast that it is more optimal to go ahead and force a flush
  	 * and wait for the transaction to be committed than it is to
  	 * wait for an arbitrary amount of time for new writers to
  	 * join the transaction.  We achieve this by measuring how
  	 * long it takes to commit a transaction, and compare it with
  	 * how long this transaction has been running, and if run time
  	 * < commit time then we sleep for the delta and commit.  This
  	 * greatly helps super fast disks that would see slowdowns as
  	 * more threads started doing fsyncs.
  	 *
  	 * But don't do this if this process was the most recent one
  	 * to perform a synchronous write.  We do this to detect the
  	 * case where a single process is doing a stream of sync
  	 * writes.  No point in waiting for joiners in that case.
  	 */
  	pid = current->pid;
  	if (handle->h_sync && journal->j_last_sync_writer != pid) {
  		u64 commit_time, trans_time;
  
  		journal->j_last_sync_writer = pid;
  
  		read_lock(&journal->j_state_lock);
  		commit_time = journal->j_average_commit_time;
  		read_unlock(&journal->j_state_lock);
  
  		trans_time = ktime_to_ns(ktime_sub(ktime_get(),
  						   transaction->t_start_time));
  
  		commit_time = max_t(u64, commit_time,
  				    1000*journal->j_min_batch_time);
  		commit_time = min_t(u64, commit_time,
  				    1000*journal->j_max_batch_time);
  
  		if (trans_time < commit_time) {
  			ktime_t expires = ktime_add_ns(ktime_get(),
  						       commit_time);
  			set_current_state(TASK_UNINTERRUPTIBLE);
  			schedule_hrtimeout(&expires, HRTIMER_MODE_ABS);
  		}
  	}
  
  	if (handle->h_sync)
  		transaction->t_synchronous_commit = 1;
  	current->journal_info = NULL;
  	atomic_sub(handle->h_buffer_credits,
  		   &transaction->t_outstanding_credits);
  
  	/*
  	 * If the handle is marked SYNC, we need to set another commit
  	 * going!  We also want to force a commit if the current
  	 * transaction is occupying too much of the log, or if the
  	 * transaction is too old now.
  	 */
  	if (handle->h_sync ||
  	    (atomic_read(&transaction->t_outstanding_credits) >
  	     journal->j_max_transaction_buffers) ||
  	    time_after_eq(jiffies, transaction->t_expires)) {
  		/* Do this even for aborted journals: an abort still
  		 * completes the commit thread, it just doesn't write
  		 * anything to disk. */
  
  		jbd_debug(2, "transaction too old, requesting commit for "
  					"handle %p\n", handle);
  		/* This is non-blocking */
  		jbd2_log_start_commit(journal, transaction->t_tid);
  
  		/*
  		 * Special case: JBD2_SYNC synchronous updates require us
  		 * to wait for the commit to complete.
  		 */
  		if (handle->h_sync && !(current->flags & PF_MEMALLOC))
  			wait_for_commit = 1;
  	}
  
  	/*
  	 * Once we drop t_updates, if it goes to zero the transaction
  	 * could start committing on us and eventually disappear.  So
  	 * once we do this, we must not dereference transaction
  	 * pointer again.
  	 */
  	tid = transaction->t_tid;
  	if (atomic_dec_and_test(&transaction->t_updates)) {
  		wake_up(&journal->j_wait_updates);
  		if (journal->j_barrier_count)
  			wake_up(&journal->j_wait_transaction_locked);
  	}
  
  	if (wait_for_commit)
  		err = jbd2_log_wait_commit(journal, tid);
  
  	lock_map_release(&handle->h_lockdep_map);
  
  	jbd2_free_handle(handle);
  	return err;
  }
  
  /**
   * int jbd2_journal_force_commit() - force any uncommitted transactions
   * @journal: journal to force
   *
   * For synchronous operations: force any uncommitted transactions
   * to disk.  May seem kludgy, but it reuses all the handle batching
   * code in a very simple manner.
   */
  int jbd2_journal_force_commit(journal_t *journal)
  {
  	handle_t *handle;
  	int ret;
  
  	handle = jbd2_journal_start(journal, 1);
  	if (IS_ERR(handle)) {
  		ret = PTR_ERR(handle);
  	} else {
  		handle->h_sync = 1;
  		ret = jbd2_journal_stop(handle);
  	}
  	return ret;
  }
  
  /*
   *
   * List management code snippets: various functions for manipulating the
   * transaction buffer lists.
   *
   */
  
  /*
   * Append a buffer to a transaction list, given the transaction's list head
   * pointer.
   *
   * j_list_lock is held.
   *
   * jbd_lock_bh_state(jh2bh(jh)) is held.
   */
  
  static inline void
  __blist_add_buffer(struct journal_head **list, struct journal_head *jh)
  {
  	if (!*list) {
  		jh->b_tnext = jh->b_tprev = jh;
  		*list = jh;
  	} else {
  		/* Insert at the tail of the list to preserve order */
  		struct journal_head *first = *list, *last = first->b_tprev;
  		jh->b_tprev = last;
  		jh->b_tnext = first;
  		last->b_tnext = first->b_tprev = jh;
  	}
  }
  
  /*
   * Remove a buffer from a transaction list, given the transaction's list
   * head pointer.
   *
   * Called with j_list_lock held, and the journal may not be locked.
   *
   * jbd_lock_bh_state(jh2bh(jh)) is held.
   */
  
  static inline void
  __blist_del_buffer(struct journal_head **list, struct journal_head *jh)
  {
  	if (*list == jh) {
  		*list = jh->b_tnext;
  		if (*list == jh)
  			*list = NULL;
  	}
  	jh->b_tprev->b_tnext = jh->b_tnext;
  	jh->b_tnext->b_tprev = jh->b_tprev;
  }
  
  /*
   * Remove a buffer from the appropriate transaction list.
   *
   * Note that this function can *change* the value of
   * bh->b_transaction->t_buffers, t_forget, t_iobuf_list, t_shadow_list,
   * t_log_list or t_reserved_list.  If the caller is holding onto a copy of one
   * of these pointers, it could go bad.  Generally the caller needs to re-read
   * the pointer from the transaction_t.
   *
   * Called under j_list_lock.  The journal may not be locked.
   */
  void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
  {
  	struct journal_head **list = NULL;
  	transaction_t *transaction;
  	struct buffer_head *bh = jh2bh(jh);
  
  	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
  	transaction = jh->b_transaction;
  	if (transaction)
  		assert_spin_locked(&transaction->t_journal->j_list_lock);
  
  	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
  	if (jh->b_jlist != BJ_None)
  		J_ASSERT_JH(jh, transaction != NULL);
  
  	switch (jh->b_jlist) {
  	case BJ_None:
  		return;
  	case BJ_Metadata:
  		transaction->t_nr_buffers--;
  		J_ASSERT_JH(jh, transaction->t_nr_buffers >= 0);
  		list = &transaction->t_buffers;
  		break;
  	case BJ_Forget:
  		list = &transaction->t_forget;
  		break;
  	case BJ_IO:
  		list = &transaction->t_iobuf_list;
  		break;
  	case BJ_Shadow:
  		list = &transaction->t_shadow_list;
  		break;
  	case BJ_LogCtl:
  		list = &transaction->t_log_list;
  		break;
  	case BJ_Reserved:
  		list = &transaction->t_reserved_list;
  		break;
  	}
  
  	__blist_del_buffer(list, jh);
  	jh->b_jlist = BJ_None;
  	if (test_clear_buffer_jbddirty(bh))
  		mark_buffer_dirty(bh);	/* Expose it to the VM */
  }
  
  /*
   * Remove buffer from all transactions.
   *
   * Called with bh_state lock and j_list_lock
   *
   * jh and bh may be already freed when this function returns.
   */
  static void __jbd2_journal_unfile_buffer(struct journal_head *jh)
  {
  	__jbd2_journal_temp_unlink_buffer(jh);
  	jh->b_transaction = NULL;
  	jbd2_journal_put_journal_head(jh);
  }
  
  void jbd2_journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
  {
  	struct buffer_head *bh = jh2bh(jh);
  
  	/* Get reference so that buffer cannot be freed before we unlock it */
  	get_bh(bh);
  	jbd_lock_bh_state(bh);
  	spin_lock(&journal->j_list_lock);
  	__jbd2_journal_unfile_buffer(jh);
  	spin_unlock(&journal->j_list_lock);
  	jbd_unlock_bh_state(bh);
  	__brelse(bh);
  }
  
  /*
   * Called from jbd2_journal_try_to_free_buffers().
   *
   * Called under jbd_lock_bh_state(bh)
   */
  static void
  __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
  {
  	struct journal_head *jh;
  
  	jh = bh2jh(bh);
  
  	if (buffer_locked(bh) || buffer_dirty(bh))
  		goto out;
  
  	if (jh->b_next_transaction != NULL)
  		goto out;
  
  	spin_lock(&journal->j_list_lock);
  	if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) {
  		/* written-back checkpointed metadata buffer */
  		if (jh->b_jlist == BJ_None) {
  			JBUFFER_TRACE(jh, "remove from checkpoint list");
  			__jbd2_journal_remove_checkpoint(jh);
  		}
  	}
  	spin_unlock(&journal->j_list_lock);
  out:
  	return;
  }
  
  /**
   * int jbd2_journal_try_to_free_buffers() - try to free page buffers.
   * @journal: journal for operation
   * @page: to try and free
   * @gfp_mask: we use the mask to detect how hard should we try to release
   * buffers. If __GFP_WAIT and __GFP_FS is set, we wait for commit code to
   * release the buffers.
   *
   *
   * For all the buffers on this page,
   * if they are fully written out ordered data, move them onto BUF_CLEAN
   * so try_to_free_buffers() can reap them.
   *
   * This function returns non-zero if we wish try_to_free_buffers()
   * to be called. We do this if the page is releasable by try_to_free_buffers().
   * We also do it if the page has locked or dirty buffers and the caller wants
   * us to perform sync or async writeout.
   *
   * This complicates JBD locking somewhat.  We aren't protected by the
   * BKL here.  We wish to remove the buffer from its committing or
   * running transaction's ->t_datalist via __jbd2_journal_unfile_buffer.
   *
   * This may *change* the value of transaction_t->t_datalist, so anyone
   * who looks at t_datalist needs to lock against this function.
   *
   * Even worse, someone may be doing a jbd2_journal_dirty_data on this
   * buffer.  So we need to lock against that.  jbd2_journal_dirty_data()
   * will come out of the lock with the buffer dirty, which makes it
   * ineligible for release here.
   *
   * Who else is affected by this?  hmm...  Really the only contender
   * is do_get_write_access() - it could be looking at the buffer while
   * journal_try_to_free_buffer() is changing its state.  But that
   * cannot happen because we never reallocate freed data as metadata
   * while the data is part of a transaction.  Yes?
   *
   * Return 0 on failure, 1 on success
   */
  int jbd2_journal_try_to_free_buffers(journal_t *journal,
  				struct page *page, gfp_t gfp_mask)
  {
  	struct buffer_head *head;
  	struct buffer_head *bh;
  	int ret = 0;
  
  	J_ASSERT(PageLocked(page));
  
  	head = page_buffers(page);
  	bh = head;
  	do {
  		struct journal_head *jh;
  
  		/*
  		 * We take our own ref against the journal_head here to avoid
  		 * having to add tons of locking around each instance of
  		 * jbd2_journal_put_journal_head().
  		 */
  		jh = jbd2_journal_grab_journal_head(bh);
  		if (!jh)
  			continue;
  
  		jbd_lock_bh_state(bh);
  		__journal_try_to_free_buffer(journal, bh);
  		jbd2_journal_put_journal_head(jh);
  		jbd_unlock_bh_state(bh);
  		if (buffer_jbd(bh))
  			goto busy;
  	} while ((bh = bh->b_this_page) != head);
  
  	ret = try_to_free_buffers(page);
  
  busy:
  	return ret;
  }
  
  /*
   * This buffer is no longer needed.  If it is on an older transaction's
   * checkpoint list we need to record it on this transaction's forget list
   * to pin this buffer (and hence its checkpointing transaction) down until
   * this transaction commits.  If the buffer isn't on a checkpoint list, we
   * release it.
   * Returns non-zero if JBD no longer has an interest in the buffer.
   *
   * Called under j_list_lock.
   *
   * Called under jbd_lock_bh_state(bh).
   */
  static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
  {
  	int may_free = 1;
  	struct buffer_head *bh = jh2bh(jh);
  
  	if (jh->b_cp_transaction) {
  		JBUFFER_TRACE(jh, "on running+cp transaction");
  		__jbd2_journal_temp_unlink_buffer(jh);
  		/*
  		 * We don't want to write the buffer anymore, clear the
  		 * bit so that we don't confuse checks in
  		 * __journal_file_buffer
  		 */
  		clear_buffer_dirty(bh);
  		__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
  		may_free = 0;
  	} else {
  		JBUFFER_TRACE(jh, "on running transaction");
  		__jbd2_journal_unfile_buffer(jh);
  	}
  	return may_free;
  }
  
  /*
   * jbd2_journal_invalidatepage
   *
   * This code is tricky.  It has a number of cases to deal with.
   *
   * There are two invariants which this code relies on:
   *
   * i_size must be updated on disk before we start calling invalidatepage on the
   * data.
   *
   *  This is done in ext3 by defining an ext3_setattr method which
   *  updates i_size before truncate gets going.  By maintaining this
   *  invariant, we can be sure that it is safe to throw away any buffers
   *  attached to the current transaction: once the transaction commits,
   *  we know that the data will not be needed.
   *
   *  Note however that we can *not* throw away data belonging to the
   *  previous, committing transaction!
   *
   * Any disk blocks which *are* part of the previous, committing
   * transaction (and which therefore cannot be discarded immediately) are
   * not going to be reused in the new running transaction
   *
   *  The bitmap committed_data images guarantee this: any block which is
   *  allocated in one transaction and removed in the next will be marked
   *  as in-use in the committed_data bitmap, so cannot be reused until
   *  the next transaction to delete the block commits.  This means that
   *  leaving committing buffers dirty is quite safe: the disk blocks
   *  cannot be reallocated to a different file and so buffer aliasing is
   *  not possible.
   *
   *
   * The above applies mainly to ordered data mode.  In writeback mode we
   * don't make guarantees about the order in which data hits disk --- in
   * particular we don't guarantee that new dirty data is flushed before
   * transaction commit --- so it is always safe just to discard data
   * immediately in that mode.  --sct
   */
  
  /*
   * The journal_unmap_buffer helper function returns zero if the buffer
   * concerned remains pinned as an anonymous buffer belonging to an older
   * transaction.
   *
   * We're outside-transaction here.  Either or both of j_running_transaction
   * and j_committing_transaction may be NULL.
   */
  static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh)
  {
  	transaction_t *transaction;
  	struct journal_head *jh;
  	int may_free = 1;
  	int ret;
  
  	BUFFER_TRACE(bh, "entry");
  
  	/*
  	 * It is safe to proceed here without the j_list_lock because the
  	 * buffers cannot be stolen by try_to_free_buffers as long as we are
  	 * holding the page lock. --sct
  	 */
  
  	if (!buffer_jbd(bh))
  		goto zap_buffer_unlocked;
  
  	/* OK, we have data buffer in journaled mode */
  	write_lock(&journal->j_state_lock);
  	jbd_lock_bh_state(bh);
  	spin_lock(&journal->j_list_lock);
  
  	jh = jbd2_journal_grab_journal_head(bh);
  	if (!jh)
  		goto zap_buffer_no_jh;
  
  	/*
  	 * We cannot remove the buffer from checkpoint lists until the
  	 * transaction adding inode to orphan list (let's call it T)
  	 * is committed.  Otherwise if the transaction changing the
  	 * buffer would be cleaned from the journal before T is
  	 * committed, a crash will cause that the correct contents of
  	 * the buffer will be lost.  On the other hand we have to
  	 * clear the buffer dirty bit at latest at the moment when the
  	 * transaction marking the buffer as freed in the filesystem
  	 * structures is committed because from that moment on the
  	 * buffer can be reallocated and used by a different page.
  	 * Since the block hasn't been freed yet but the inode has
  	 * already been added to orphan list, it is safe for us to add
  	 * the buffer to BJ_Forget list of the newest transaction.
  	 */
  	transaction = jh->b_transaction;
  	if (transaction == NULL) {
  		/* First case: not on any transaction.  If it
  		 * has no checkpoint link, then we can zap it:
  		 * it's a writeback-mode buffer so we don't care
  		 * if it hits disk safely. */
  		if (!jh->b_cp_transaction) {
  			JBUFFER_TRACE(jh, "not on any transaction: zap");
  			goto zap_buffer;
  		}
  
  		if (!buffer_dirty(bh)) {
  			/* bdflush has written it.  We can drop it now */
  			goto zap_buffer;
  		}
  
  		/* OK, it must be in the journal but still not
  		 * written fully to disk: it's metadata or
  		 * journaled data... */
  
  		if (journal->j_running_transaction) {
  			/* ... and once the current transaction has
  			 * committed, the buffer won't be needed any
  			 * longer. */
  			JBUFFER_TRACE(jh, "checkpointed: add to BJ_Forget");
  			ret = __dispose_buffer(jh,
  					journal->j_running_transaction);
  			jbd2_journal_put_journal_head(jh);
  			spin_unlock(&journal->j_list_lock);
  			jbd_unlock_bh_state(bh);
  			write_unlock(&journal->j_state_lock);
  			return ret;
  		} else {
  			/* There is no currently-running transaction. So the
  			 * orphan record which we wrote for this file must have
  			 * passed into commit.  We must attach this buffer to
  			 * the committing transaction, if it exists. */
  			if (journal->j_committing_transaction) {
  				JBUFFER_TRACE(jh, "give to committing trans");
  				ret = __dispose_buffer(jh,
  					journal->j_committing_transaction);
  				jbd2_journal_put_journal_head(jh);
  				spin_unlock(&journal->j_list_lock);
  				jbd_unlock_bh_state(bh);
  				write_unlock(&journal->j_state_lock);
  				return ret;
  			} else {
  				/* The orphan record's transaction has
  				 * committed.  We can cleanse this buffer */
  				clear_buffer_jbddirty(bh);
  				goto zap_buffer;
  			}
  		}
  	} else if (transaction == journal->j_committing_transaction) {
  		JBUFFER_TRACE(jh, "on committing transaction");
  		/*
  		 * The buffer is committing, we simply cannot touch
  		 * it. So we just set j_next_transaction to the
  		 * running transaction (if there is one) and mark
  		 * buffer as freed so that commit code knows it should
  		 * clear dirty bits when it is done with the buffer.
  		 */
  		set_buffer_freed(bh);
  		if (journal->j_running_transaction && buffer_jbddirty(bh))
  			jh->b_next_transaction = journal->j_running_transaction;
  		jbd2_journal_put_journal_head(jh);
  		spin_unlock(&journal->j_list_lock);
  		jbd_unlock_bh_state(bh);
  		write_unlock(&journal->j_state_lock);
  		return 0;
  	} else {
  		/* Good, the buffer belongs to the running transaction.
  		 * We are writing our own transaction's data, not any
  		 * previous one's, so it is safe to throw it away
  		 * (remember that we expect the filesystem to have set
  		 * i_size already for this truncate so recovery will not
  		 * expose the disk blocks we are discarding here.) */
  		J_ASSERT_JH(jh, transaction == journal->j_running_transaction);
  		JBUFFER_TRACE(jh, "on running transaction");
  		may_free = __dispose_buffer(jh, transaction);
  	}
  
  zap_buffer:
  	jbd2_journal_put_journal_head(jh);
  zap_buffer_no_jh:
  	spin_unlock(&journal->j_list_lock);
  	jbd_unlock_bh_state(bh);
  	write_unlock(&journal->j_state_lock);
  zap_buffer_unlocked:
  	clear_buffer_dirty(bh);
  	J_ASSERT_BH(bh, !buffer_jbddirty(bh));
  	clear_buffer_mapped(bh);
  	clear_buffer_req(bh);
  	clear_buffer_new(bh);
  	bh->b_bdev = NULL;
  	return may_free;
  }
  
  /**
   * void jbd2_journal_invalidatepage()
   * @journal: journal to use for flush...
   * @page:    page to flush
   * @offset:  length of page to invalidate.
   *
   * Reap page buffers containing data after offset in page.
   *
   */
  void jbd2_journal_invalidatepage(journal_t *journal,
  		      struct page *page,
  		      unsigned long offset)
  {
  	struct buffer_head *head, *bh, *next;
  	unsigned int curr_off = 0;
  	int may_free = 1;
  
  	if (!PageLocked(page))
  		BUG();
  	if (!page_has_buffers(page))
  		return;
  
  	/* We will potentially be playing with lists other than just the
  	 * data lists (especially for journaled data mode), so be
  	 * cautious in our locking. */
  
  	head = bh = page_buffers(page);
  	do {
  		unsigned int next_off = curr_off + bh->b_size;
  		next = bh->b_this_page;
  
  		if (offset <= curr_off) {
  			/* This block is wholly outside the truncation point */
  			lock_buffer(bh);
  			may_free &= journal_unmap_buffer(journal, bh);
  			unlock_buffer(bh);
  		}
  		curr_off = next_off;
  		bh = next;
  
  	} while (bh != head);
  
  	if (!offset) {
  		if (may_free && try_to_free_buffers(page))
  			J_ASSERT(!page_has_buffers(page));
  	}
  }
  
  /*
   * File a buffer on the given transaction list.
   */
  void __jbd2_journal_file_buffer(struct journal_head *jh,
  			transaction_t *transaction, int jlist)
  {
  	struct journal_head **list = NULL;
  	int was_dirty = 0;
  	struct buffer_head *bh = jh2bh(jh);
  
  	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
  	assert_spin_locked(&transaction->t_journal->j_list_lock);
  
  	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
  	J_ASSERT_JH(jh, jh->b_transaction == transaction ||
  				jh->b_transaction == NULL);
  
  	if (jh->b_transaction && jh->b_jlist == jlist)
  		return;
  
  	if (jlist == BJ_Metadata || jlist == BJ_Reserved ||
  	    jlist == BJ_Shadow || jlist == BJ_Forget) {
  		/*
  		 * For metadata buffers, we track dirty bit in buffer_jbddirty
  		 * instead of buffer_dirty. We should not see a dirty bit set
  		 * here because we clear it in do_get_write_access but e.g.
  		 * tune2fs can modify the sb and set the dirty bit at any time
  		 * so we try to gracefully handle that.
  		 */
  		if (buffer_dirty(bh))
  			warn_dirty_buffer(bh);
  		if (test_clear_buffer_dirty(bh) ||
  		    test_clear_buffer_jbddirty(bh))
  			was_dirty = 1;
  	}
  
  	if (jh->b_transaction)
  		__jbd2_journal_temp_unlink_buffer(jh);
  	else
  		jbd2_journal_grab_journal_head(bh);
  	jh->b_transaction = transaction;
  
  	switch (jlist) {
  	case BJ_None:
  		J_ASSERT_JH(jh, !jh->b_committed_data);
  		J_ASSERT_JH(jh, !jh->b_frozen_data);
  		return;
  	case BJ_Metadata:
  		transaction->t_nr_buffers++;
  		list = &transaction->t_buffers;
  		break;
  	case BJ_Forget:
  		list = &transaction->t_forget;
  		break;
  	case BJ_IO:
  		list = &transaction->t_iobuf_list;
  		break;
  	case BJ_Shadow:
  		list = &transaction->t_shadow_list;
  		break;
  	case BJ_LogCtl:
  		list = &transaction->t_log_list;
  		break;
  	case BJ_Reserved:
  		list = &transaction->t_reserved_list;
  		break;
  	}
  
  	__blist_add_buffer(list, jh);
  	jh->b_jlist = jlist;
  
  	if (was_dirty)
  		set_buffer_jbddirty(bh);
  }
  
  void jbd2_journal_file_buffer(struct journal_head *jh,
  				transaction_t *transaction, int jlist)
  {
  	jbd_lock_bh_state(jh2bh(jh));
  	spin_lock(&transaction->t_journal->j_list_lock);
  	__jbd2_journal_file_buffer(jh, transaction, jlist);
  	spin_unlock(&transaction->t_journal->j_list_lock);
  	jbd_unlock_bh_state(jh2bh(jh));
  }
  
  /*
   * Remove a buffer from its current buffer list in preparation for
   * dropping it from its current transaction entirely.  If the buffer has
   * already started to be used by a subsequent transaction, refile the
   * buffer on that transaction's metadata list.
   *
   * Called under j_list_lock
   * Called under jbd_lock_bh_state(jh2bh(jh))
   *
   * jh and bh may be already free when this function returns
   */
  void __jbd2_journal_refile_buffer(struct journal_head *jh)
  {
  	int was_dirty, jlist;
  	struct buffer_head *bh = jh2bh(jh);
  
  	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
  	if (jh->b_transaction)
  		assert_spin_locked(&jh->b_transaction->t_journal->j_list_lock);
  
  	/* If the buffer is now unused, just drop it. */
  	if (jh->b_next_transaction == NULL) {
  		__jbd2_journal_unfile_buffer(jh);
  		return;
  	}
  
  	/*
  	 * It has been modified by a later transaction: add it to the new
  	 * transaction's metadata list.
  	 */
  
  	was_dirty = test_clear_buffer_jbddirty(bh);
  	__jbd2_journal_temp_unlink_buffer(jh);
  	/*
  	 * We set b_transaction here because b_next_transaction will inherit
  	 * our jh reference and thus __jbd2_journal_file_buffer() must not
  	 * take a new one.
  	 */
  	jh->b_transaction = jh->b_next_transaction;
  	jh->b_next_transaction = NULL;
  	if (buffer_freed(bh))
  		jlist = BJ_Forget;
  	else if (jh->b_modified)
  		jlist = BJ_Metadata;
  	else
  		jlist = BJ_Reserved;
  	__jbd2_journal_file_buffer(jh, jh->b_transaction, jlist);
  	J_ASSERT_JH(jh, jh->b_transaction->t_state == T_RUNNING);
  
  	if (was_dirty)
  		set_buffer_jbddirty(bh);
  }
  
  /*
   * __jbd2_journal_refile_buffer() with necessary locking added. We take our
   * bh reference so that we can safely unlock bh.
   *
   * The jh and bh may be freed by this call.
   */
  void jbd2_journal_refile_buffer(journal_t *journal, struct journal_head *jh)
  {
  	struct buffer_head *bh = jh2bh(jh);
  
  	/* Get reference so that buffer cannot be freed before we unlock it */
  	get_bh(bh);
  	jbd_lock_bh_state(bh);
  	spin_lock(&journal->j_list_lock);
  	__jbd2_journal_refile_buffer(jh);
  	jbd_unlock_bh_state(bh);
  	spin_unlock(&journal->j_list_lock);
  	__brelse(bh);
  }
  
  /*
   * File inode in the inode list of the handle's transaction
   */
  int jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *jinode)
  {
  	transaction_t *transaction = handle->h_transaction;
  	journal_t *journal = transaction->t_journal;
  
  	if (is_handle_aborted(handle))
  		return -EIO;
  
  	jbd_debug(4, "Adding inode %lu, tid:%d\n", jinode->i_vfs_inode->i_ino,
  			transaction->t_tid);
  
  	/*
  	 * First check whether inode isn't already on the transaction's
  	 * lists without taking the lock. Note that this check is safe
  	 * without the lock as we cannot race with somebody removing inode
  	 * from the transaction. The reason is that we remove inode from the
  	 * transaction only in journal_release_jbd_inode() and when we commit
  	 * the transaction. We are guarded from the first case by holding
  	 * a reference to the inode. We are safe against the second case
  	 * because if jinode->i_transaction == transaction, commit code
  	 * cannot touch the transaction because we hold reference to it,
  	 * and if jinode->i_next_transaction == transaction, commit code
  	 * will only file the inode where we want it.
  	 */
  	if (jinode->i_transaction == transaction ||
  	    jinode->i_next_transaction == transaction)
  		return 0;
  
  	spin_lock(&journal->j_list_lock);
  
  	if (jinode->i_transaction == transaction ||
  	    jinode->i_next_transaction == transaction)
  		goto done;
  
  	/*
  	 * We only ever set this variable to 1 so the test is safe. Since
  	 * t_need_data_flush is likely to be set, we do the test to save some
  	 * cacheline bouncing
  	 */
  	if (!transaction->t_need_data_flush)
  		transaction->t_need_data_flush = 1;
  	/* On some different transaction's list - should be
  	 * the committing one */
  	if (jinode->i_transaction) {
  		J_ASSERT(jinode->i_next_transaction == NULL);
  		J_ASSERT(jinode->i_transaction ==
  					journal->j_committing_transaction);
  		jinode->i_next_transaction = transaction;
  		goto done;
  	}
  	/* Not on any transaction list... */
  	J_ASSERT(!jinode->i_next_transaction);
  	jinode->i_transaction = transaction;
  	list_add(&jinode->i_list, &transaction->t_inode_list);
  done:
  	spin_unlock(&journal->j_list_lock);
  
  	return 0;
  }
  
  /*
   * File truncate and transaction commit interact with each other in a
   * non-trivial way.  If a transaction writing data block A is
   * committing, we cannot discard the data by truncate until we have
   * written them.  Otherwise if we crashed after the transaction with
   * write has committed but before the transaction with truncate has
   * committed, we could see stale data in block A.  This function is a
   * helper to solve this problem.  It starts writeout of the truncated
   * part in case it is in the committing transaction.
   *
   * Filesystem code must call this function when inode is journaled in
   * ordered mode before truncation happens and after the inode has been
   * placed on orphan list with the new inode size. The second condition
   * avoids the race that someone writes new data and we start
   * committing the transaction after this function has been called but
   * before a transaction for truncate is started (and furthermore it
   * allows us to optimize the case where the addition to orphan list
   * happens in the same transaction as write --- we don't have to write
   * any data in such case).
   */
  int jbd2_journal_begin_ordered_truncate(journal_t *journal,
  					struct jbd2_inode *jinode,
  					loff_t new_size)
  {
  	transaction_t *inode_trans, *commit_trans;
  	int ret = 0;
  
  	/* This is a quick check to avoid locking if not necessary */
  	if (!jinode->i_transaction)
  		goto out;
  	/* Locks are here just to force reading of recent values, it is
  	 * enough that the transaction was not committing before we started
  	 * a transaction adding the inode to orphan list */
  	read_lock(&journal->j_state_lock);
  	commit_trans = journal->j_committing_transaction;
  	read_unlock(&journal->j_state_lock);
  	spin_lock(&journal->j_list_lock);
  	inode_trans = jinode->i_transaction;
  	spin_unlock(&journal->j_list_lock);
  	if (inode_trans == commit_trans) {
  		ret = filemap_fdatawrite_range(jinode->i_vfs_inode->i_mapping,
  			new_size, LLONG_MAX);
  		if (ret)
  			jbd2_journal_abort(journal, ret);
  	}
  out:
  	return ret;
  }
  