Initial import

1 files changed, 2487 insertions, 0 deletions

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
new file mode 100644
index 000000000..ff2f2e6ad
--- /dev/null
+++ b/fs/jbd2/transaction.c
@@ -0,0 +1,2487 @@
+/*
+ * 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>
+
+#include <trace/events/jbd2.h>
+
+static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
+static void __jbd2_journal_unfile_buffer(struct journal_head *jh);
+
+static struct kmem_cache *transaction_cache;
+int __init jbd2_journal_init_transaction_cache(void)
+{
+	J_ASSERT(!transaction_cache);
+	transaction_cache = kmem_cache_create("jbd2_transaction_s",
+					sizeof(transaction_t),
+					0,
+					SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
+					NULL);
+	if (transaction_cache)
+		return 0;
+	return -ENOMEM;
+}
+
+void jbd2_journal_destroy_transaction_cache(void)
+{
+	if (transaction_cache) {
+		kmem_cache_destroy(transaction_cache);
+		transaction_cache = NULL;
+	}
+}
+
+void jbd2_journal_free_transaction(transaction_t *transaction)
+{
+	if (unlikely(ZERO_OR_NULL_PTR(transaction)))
+		return;
+	kmem_cache_free(transaction_cache, transaction);
+}
+
+/*
+ * 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,
+		   atomic_read(&journal->j_reserved_credits));
+	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;
+	transaction->t_requested = 0;
+
+	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
+}
+
+/*
+ * Wait until running transaction passes T_LOCKED state. Also starts the commit
+ * if needed. The function expects running transaction to exist and releases
+ * j_state_lock.
+ */
+static void wait_transaction_locked(journal_t *journal)
+	__releases(journal->j_state_lock)
+{
+	DEFINE_WAIT(wait);
+	int need_to_start;
+	tid_t tid = journal->j_running_transaction->t_tid;
+
+	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+			TASK_UNINTERRUPTIBLE);
+	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);
+}
+
+static void sub_reserved_credits(journal_t *journal, int blocks)
+{
+	atomic_sub(blocks, &journal->j_reserved_credits);
+	wake_up(&journal->j_wait_reserved);
+}
+
+/*
+ * Wait until we can add credits for handle to the running transaction.  Called
+ * with j_state_lock held for reading. Returns 0 if handle joined the running
+ * transaction. Returns 1 if we had to wait, j_state_lock is dropped, and
+ * caller must retry.
+ */
+static int add_transaction_credits(journal_t *journal, int blocks,
+				   int rsv_blocks)
+{
+	transaction_t *t = journal->j_running_transaction;
+	int needed;
+	int total = blocks + rsv_blocks;
+
+	/*
+	 * If the current transaction is locked down for commit, wait
+	 * for the lock to be released.
+	 */
+	if (t->t_state == T_LOCKED) {
+		wait_transaction_locked(journal);
+		return 1;
+	}
+
+	/*
+	 * 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(total, &t->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.
+		 */
+		atomic_sub(total, &t->t_outstanding_credits);
+		wait_transaction_locked(journal);
+		return 1;
+	}
+
+	/*
+	 * 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.
+	 */
+	if (jbd2_log_space_left(journal) < jbd2_space_needed(journal)) {
+		atomic_sub(total, &t->t_outstanding_credits);
+		read_unlock(&journal->j_state_lock);
+		write_lock(&journal->j_state_lock);
+		if (jbd2_log_space_left(journal) < jbd2_space_needed(journal))
+			__jbd2_log_wait_for_space(journal);
+		write_unlock(&journal->j_state_lock);
+		return 1;
+	}
+
+	/* No reservation? We are done... */
+	if (!rsv_blocks)
+		return 0;
+
+	needed = atomic_add_return(rsv_blocks, &journal->j_reserved_credits);
+	/* We allow at most half of a transaction to be reserved */
+	if (needed > journal->j_max_transaction_buffers / 2) {
+		sub_reserved_credits(journal, rsv_blocks);
+		atomic_sub(total, &t->t_outstanding_credits);
+		read_unlock(&journal->j_state_lock);
+		wait_event(journal->j_wait_reserved,
+			 atomic_read(&journal->j_reserved_credits) + rsv_blocks
+			 <= journal->j_max_transaction_buffers / 2);
+		return 1;
+	}
+	return 0;
+}
+
+/*
+ * 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;
+	int		blocks = handle->h_buffer_credits;
+	int		rsv_blocks = 0;
+	unsigned long ts = jiffies;
+
+	/*
+	 * 1/2 of transaction can be reserved so we can practically handle
+	 * only 1/2 of maximum transaction size per operation
+	 */
+	if (WARN_ON(blocks > journal->j_max_transaction_buffers / 2)) {
+		printk(KERN_ERR "JBD2: %s wants too many credits (%d > %d)\n",
+		       current->comm, blocks,
+		       journal->j_max_transaction_buffers / 2);
+		return -ENOSPC;
+	}
+
+	if (handle->h_rsv_handle)
+		rsv_blocks = handle->h_rsv_handle->h_buffer_credits;
+
+alloc_transaction:
+	if (!journal->j_running_transaction) {
+		new_transaction = kmem_cache_zalloc(transaction_cache,
+						    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);
+		jbd2_journal_free_transaction(new_transaction);
+		return -EROFS;
+	}
+
+	/*
+	 * Wait on the journal's transaction barrier if necessary. Specifically
+	 * we allow reserved handles to proceed because otherwise commit could
+	 * deadlock on page writeback not being able to complete.
+	 */
+	if (!handle->h_reserved && 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 &&
+		    (handle->h_reserved || !journal->j_barrier_count)) {
+			jbd2_get_transaction(journal, new_transaction);
+			new_transaction = NULL;
+		}
+		write_unlock(&journal->j_state_lock);
+		goto repeat;
+	}
+
+	transaction = journal->j_running_transaction;
+
+	if (!handle->h_reserved) {
+		/* We may have dropped j_state_lock - restart in that case */
+		if (add_transaction_credits(journal, blocks, rsv_blocks))
+			goto repeat;
+	} else {
+		/*
+		 * We have handle reserved so we are allowed to join T_LOCKED
+		 * transaction and we don't have to check for transaction size
+		 * and journal space.
+		 */
+		sub_reserved_credits(journal, blocks);
+		handle->h_reserved = 0;
+	}
+
+	/* 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;
+	handle->h_requested_credits = blocks;
+	handle->h_start_jiffies = jiffies;
+	atomic_inc(&transaction->t_updates);
+	atomic_inc(&transaction->t_handle_count);
+	jbd_debug(4, "Handle %p given %d credits (total %d, free %lu)\n",
+		  handle, blocks,
+		  atomic_read(&transaction->t_outstanding_credits),
+		  jbd2_log_space_left(journal));
+	read_unlock(&journal->j_state_lock);
+	current->journal_info = handle;
+
+	lock_map_acquire(&handle->h_lockdep_map);
+	jbd2_journal_free_transaction(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;
+	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. Additionally, if rsv_blocks > 0, we also create another
+ * handle with rsv_blocks reserved blocks in the journal. This handle is
+ * is stored in h_rsv_handle. It is not attached to any particular transaction
+ * and thus doesn't block transaction commit. If the caller uses this reserved
+ * handle, it has to set h_rsv_handle to NULL as otherwise jbd2_journal_stop()
+ * on the parent handle will dispose the reserved one. Reserved handle has to
+ * be converted to a normal handle using jbd2_journal_start_reserved() before
+ * it can be used.
+ *
+ * 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, int rsv_blocks,
+			      gfp_t gfp_mask, unsigned int type,
+			      unsigned int line_no)
+{
+	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);
+	if (rsv_blocks) {
+		handle_t *rsv_handle;
+
+		rsv_handle = new_handle(rsv_blocks);
+		if (!rsv_handle) {
+			jbd2_free_handle(handle);
+			return ERR_PTR(-ENOMEM);
+		}
+		rsv_handle->h_reserved = 1;
+		rsv_handle->h_journal = journal;
+		handle->h_rsv_handle = rsv_handle;
+	}
+
+	err = start_this_handle(journal, handle, gfp_mask);
+	if (err < 0) {
+		if (handle->h_rsv_handle)
+			jbd2_free_handle(handle->h_rsv_handle);
+		jbd2_free_handle(handle);
+		return ERR_PTR(err);
+	}
+	handle->h_type = type;
+	handle->h_line_no = line_no;
+	trace_jbd2_handle_start(journal->j_fs_dev->bd_dev,
+				handle->h_transaction->t_tid, type,
+				line_no, nblocks);
+	return handle;
+}
+EXPORT_SYMBOL(jbd2__journal_start);
+
+
+handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
+{
+	return jbd2__journal_start(journal, nblocks, 0, GFP_NOFS, 0, 0);
+}
+EXPORT_SYMBOL(jbd2_journal_start);
+
+void jbd2_journal_free_reserved(handle_t *handle)
+{
+	journal_t *journal = handle->h_journal;
+
+	WARN_ON(!handle->h_reserved);
+	sub_reserved_credits(journal, handle->h_buffer_credits);
+	jbd2_free_handle(handle);
+}
+EXPORT_SYMBOL(jbd2_journal_free_reserved);
+
+/**
+ * int jbd2_journal_start_reserved(handle_t *handle) - start reserved handle
+ * @handle: handle to start
+ *
+ * Start handle that has been previously reserved with jbd2_journal_reserve().
+ * This attaches @handle to the running transaction (or creates one if there's
+ * not transaction running). Unlike jbd2_journal_start() this function cannot
+ * block on journal commit, checkpointing, or similar stuff. It can block on
+ * memory allocation or frozen journal though.
+ *
+ * Return 0 on success, non-zero on error - handle is freed in that case.
+ */
+int jbd2_journal_start_reserved(handle_t *handle, unsigned int type,
+				unsigned int line_no)
+{
+	journal_t *journal = handle->h_journal;
+	int ret = -EIO;
+
+	if (WARN_ON(!handle->h_reserved)) {
+		/* Someone passed in normal handle? Just stop it. */
+		jbd2_journal_stop(handle);
+		return ret;
+	}
+	/*
+	 * Usefulness of mixing of reserved and unreserved handles is
+	 * questionable. So far nobody seems to need it so just error out.
+	 */
+	if (WARN_ON(current->journal_info)) {
+		jbd2_journal_free_reserved(handle);
+		return ret;
+	}
+
+	handle->h_journal = NULL;
+	/*
+	 * GFP_NOFS is here because callers are likely from writeback or
+	 * similarly constrained call sites
+	 */
+	ret = start_this_handle(journal, handle, GFP_NOFS);
+	if (ret < 0) {
+		jbd2_journal_free_reserved(handle);
+		return ret;
+	}
+	handle->h_type = type;
+	handle->h_line_no = line_no;
+	return 0;
+}
+EXPORT_SYMBOL(jbd2_journal_start_reserved);
+
+/**
+ * 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;
+	int result;
+	int wanted;
+
+	if (is_handle_aborted(handle))
+		return -EROFS;
+	journal = transaction->t_journal;
+
+	result = 1;
+
+	read_lock(&journal->j_state_lock);
+
+	/* Don't extend a locked-down transaction! */
+	if (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_add_return(nblocks,
+				   &transaction->t_outstanding_credits);
+
+	if (wanted > journal->j_max_transaction_buffers) {
+		jbd_debug(3, "denied handle %p %d blocks: "
+			  "transaction too large\n", handle, nblocks);
+		atomic_sub(nblocks, &transaction->t_outstanding_credits);
+		goto unlock;
+	}
+
+	if (wanted + (wanted >> JBD2_CONTROL_BLOCKS_SHIFT) >
+	    jbd2_log_space_left(journal)) {
+		jbd_debug(3, "denied handle %p %d blocks: "
+			  "insufficient log space\n", handle, nblocks);
+		atomic_sub(nblocks, &transaction->t_outstanding_credits);
+		goto unlock;
+	}
+
+	trace_jbd2_handle_extend(journal->j_fs_dev->bd_dev,
+				 transaction->t_tid,
+				 handle->h_type, handle->h_line_no,
+				 handle->h_buffer_credits,
+				 nblocks);
+
+	handle->h_buffer_credits += nblocks;
+	handle->h_requested_credits += nblocks;
+	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);
+	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. We preserve reserved handle if there's any attached to the
+ * passed in handle.
+ */
+int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_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;
+	journal = transaction->t_journal;
+
+	/*
+	 * 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 (handle->h_rsv_handle) {
+		sub_reserved_credits(journal,
+				     handle->h_rsv_handle->h_buffer_credits);
+	}
+	if (atomic_dec_and_test(&transaction->t_updates))
+		wake_up(&journal->j_wait_updates);
+	tid = transaction->t_tid;
+	spin_unlock(&transaction->t_handle_lock);
+	handle->h_transaction = NULL;
+	current->journal_info = NULL;
+
+	jbd_debug(2, "restarting handle %p\n", handle);
+	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 reserved handles */
+	if (atomic_read(&journal->j_reserved_credits)) {
+		write_unlock(&journal->j_state_lock);
+		wait_event(journal->j_wait_reserved,
+			   atomic_read(&journal->j_reserved_credits) == 0);
+		write_lock(&journal->j_state_lock);
+	}
+
+	/* 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 = handle->h_transaction;
+	journal_t *journal;
+	int error;
+	char *frozen_buffer = NULL;
+	int need_copy = 0;
+	unsigned long start_lock, time_lock;
+
+	if (is_handle_aborted(handle))
+		return -EROFS;
+	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. */
+
+ 	start_lock = jiffies;
+	lock_buffer(bh);
+	jbd_lock_bh_state(bh);
+
+	/* If it takes too long to lock the buffer, trace it */
+	time_lock = jbd2_time_diff(start_lock, jiffies);
+	if (time_lock > HZ/10)
+		trace_jbd2_lock_buffer_stall(bh->b_bdev->bd_dev,
+			jiffies_to_msecs(time_lock));
+
+	/* 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 (buffer_shadow(bh)) {
+			JBUFFER_TRACE(jh, "on shadow: sleep");
+			jbd_unlock_bh_state(bh);
+			wait_on_bit_io(&bh->b_state, BH_Shadow,
+				       TASK_UNINTERRUPTIBLE);
+			goto repeat;
+		}
+
+		/*
+		 * Only do the copy if the currently-owning transaction still
+		 * needs it. If buffer isn't on BJ_Metadata list, the
+		 * committing transaction is past that stage (here we use the
+		 * fact that BH_Shadow is set under bh_state lock together with
+		 * refiling to BJ_Shadow list and at this point we know the
+		 * buffer doesn't have BH_Shadow set).
+		 *
+		 * 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_Metadata || 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_ERR
+					       "%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);
+		/* 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);
+
+		/*
+		 * 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;
+	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;
+	journal = transaction->t_journal;
+	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);
+	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");
+		spin_lock(&journal->j_list_lock);
+		__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");
+		spin_lock(&journal->j_list_lock);
+		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_ERR "%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 = jbd2_journal_grab_journal_head(bh);
+
+	if (WARN_ON(!jh))
+		return;
+	jh->b_triggers = type;
+	jbd2_journal_put_journal_head(jh);
+}
+
+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;
+	struct journal_head *jh;
+	int ret = 0;
+
+	if (is_handle_aborted(handle))
+		return -EROFS;
+	journal = transaction->t_journal;
+	jh = jbd2_journal_grab_journal_head(bh);
+	if (!jh) {
+		ret = -EUCLEAN;
+		goto out;
+	}
+	jbd_debug(5, "journal_head %p\n", jh);
+	JBUFFER_TRACE(jh, "entry");
+
+	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;
+		if (handle->h_buffer_credits <= 0) {
+			ret = -ENOSPC;
+			goto out_unlock_bh;
+		}
+		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_ERR "JBD2: %s: "
+			       "jh->b_transaction (%llu, %p, %u) != "
+			       "journal->j_running_transaction (%p, %u)\n",
+			       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)) ||
+			     (jh->b_next_transaction != transaction))) {
+			printk(KERN_ERR "jbd2_journal_dirty_metadata: %s: "
+			       "bad jh for block %llu: "
+			       "transaction (%p, %u), "
+			       "jh->b_transaction (%p, %u), "
+			       "jh->b_next_transaction (%p, %u), jlist %u\n",
+			       journal->j_devname,
+			       (unsigned long long) bh->b_blocknr,
+			       transaction, transaction->t_tid,
+			       jh->b_transaction,
+			       jh->b_transaction ?
+			       jh->b_transaction->t_tid : 0,
+			       jh->b_next_transaction,
+			       jh->b_next_transaction ?
+			       jh->b_next_transaction->t_tid : 0,
+			       jh->b_jlist);
+			WARN_ON(1);
+			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, transaction, BJ_Metadata);
+	spin_unlock(&journal->j_list_lock);
+out_unlock_bh:
+	jbd_unlock_bh_state(bh);
+	jbd2_journal_put_journal_head(jh);
+out:
+	JBUFFER_TRACE(jh, "exit");
+	return ret;
+}
+
+/**
+ * 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;
+	struct journal_head *jh;
+	int drop_reserve = 0;
+	int err = 0;
+	int was_modified = 0;
+
+	if (is_handle_aborted(handle))
+		return -EROFS;
+	journal = transaction->t_journal;
+
+	BUFFER_TRACE(bh, "entry");
+
+	jbd_lock_bh_state(bh);
+
+	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 whether 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 == 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.
+		 */
+
+		spin_lock(&journal->j_list_lock);
+		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;
+			}
+		}
+		spin_unlock(&journal->j_list_lock);
+	} 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);
+			spin_lock(&journal->j_list_lock);
+			jh->b_next_transaction = NULL;
+			spin_unlock(&journal->j_list_lock);
+
+			/*
+			 * only drop a reference if this transaction modified
+			 * the buffer
+			 */
+			if (was_modified)
+				drop_reserve = 1;
+		}
+	}
+
+not_jbd:
+	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;
+	int err = 0, wait_for_commit = 0;
+	tid_t tid;
+	pid_t pid;
+
+	if (!transaction) {
+		/*
+		 * Handle is already detached from the transaction so
+		 * there is nothing to do other than decrease a refcount,
+		 * or free the handle if refcount drops to zero
+		 */
+		if (--handle->h_ref > 0) {
+			jbd_debug(4, "h_ref %d -> %d\n", handle->h_ref + 1,
+							 handle->h_ref);
+			return err;
+		} else {
+			if (handle->h_rsv_handle)
+				jbd2_free_handle(handle->h_rsv_handle);
+			goto free_and_exit;
+		}
+	}
+	journal = transaction->t_journal;
+
+	J_ASSERT(journal_current_handle() == handle);
+
+	if (is_handle_aborted(handle))
+		err = -EIO;
+	else
+		J_ASSERT(atomic_read(&transaction->t_updates) > 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);
+	trace_jbd2_handle_stats(journal->j_fs_dev->bd_dev,
+				transaction->t_tid,
+				handle->h_type, handle->h_line_no,
+				jiffies - handle->h_start_jiffies,
+				handle->h_sync, handle->h_requested_credits,
+				(handle->h_requested_credits -
+				 handle->h_buffer_credits));
+
+	/*
+	 * 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.
+	 *
+	 * Setting max_batch_time to 0 disables this completely.
+	 */
+	pid = current->pid;
+	if (handle->h_sync && journal->j_last_sync_writer != pid &&
+	    journal->j_max_batch_time) {
+		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);
+
+	if (handle->h_rsv_handle)
+		jbd2_journal_free_reserved(handle->h_rsv_handle);
+free_and_exit:
+	jbd2_free_handle(handle);
+	return err;
+}
+
+/*
+ *
+ * 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_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.
+ */
+static 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_Shadow:
+		list = &transaction->t_shadow_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 || jh->b_transaction != NULL)
+		goto out;
+
+	spin_lock(&journal->j_list_lock);
+	if (jh->b_cp_transaction != NULL) {
+		/* written-back checkpointed metadata buffer */
+		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,
+				int partial_page)
+{
+	transaction_t *transaction;
+	struct journal_head *jh;
+	int may_free = 1;
+
+	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
+	 * block 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.
+	 *
+	 * Also we have to clear buffer_mapped flag of a truncated buffer
+	 * because the buffer_head may be attached to the page straddling
+	 * i_size (can happen only when blocksize < pagesize) and thus the
+	 * buffer_head can be reused when the file is extended again. So we end
+	 * up keeping around invalidated buffers attached to transactions'
+	 * BJ_Forget list just to stop checkpointing code from cleaning up
+	 * the transaction this buffer was modified in.
+	 */
+	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");
+			may_free = __dispose_buffer(jh,
+					journal->j_running_transaction);
+			goto zap_buffer;
+		} 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");
+				may_free = __dispose_buffer(jh,
+					journal->j_committing_transaction);
+				goto zap_buffer;
+			} 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. If the page is straddling i_size we have to wait
+		 * for commit and try again.
+		 */
+		if (partial_page) {
+			jbd2_journal_put_journal_head(jh);
+			spin_unlock(&journal->j_list_lock);
+			jbd_unlock_bh_state(bh);
+			write_unlock(&journal->j_state_lock);
+			return -EBUSY;
+		}
+		/*
+		 * OK, buffer won't be reachable after truncate. 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:
+	/*
+	 * This is tricky. Although the buffer is truncated, it may be reused
+	 * if blocksize < pagesize and it is attached to the page straddling
+	 * EOF. Since the buffer might have been added to BJ_Forget list of the
+	 * running transaction, journal_get_write_access() won't clear
+	 * b_modified and credit accounting gets confused. So clear b_modified
+	 * here.
+	 */
+	jh->b_modified = 0;
+	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);
+	clear_buffer_delay(bh);
+	clear_buffer_unwritten(bh);
+	bh->b_bdev = NULL;
+	return may_free;
+}
+
+/**
+ * void jbd2_journal_invalidatepage()
+ * @journal: journal to use for flush...
+ * @page:    page to flush
+ * @offset:  start of the range to invalidate
+ * @length:  length of the range to invalidate
+ *
+ * Reap page buffers containing data after in the specified range in page.
+ * Can return -EBUSY if buffers are part of the committing transaction and
+ * the page is straddling i_size. Caller then has to wait for current commit
+ * and try again.
+ */
+int jbd2_journal_invalidatepage(journal_t *journal,
+				struct page *page,
+				unsigned int offset,
+				unsigned int length)
+{
+	struct buffer_head *head, *bh, *next;
+	unsigned int stop = offset + length;
+	unsigned int curr_off = 0;
+	int partial_page = (offset || length < PAGE_CACHE_SIZE);
+	int may_free = 1;
+	int ret = 0;
+
+	if (!PageLocked(page))
+		BUG();
+	if (!page_has_buffers(page))
+		return 0;
+
+	BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);
+
+	/* 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 (next_off > stop)
+			return 0;
+
+		if (offset <= curr_off) {
+			/* This block is wholly outside the truncation point */
+			lock_buffer(bh);
+			ret = journal_unmap_buffer(journal, bh, partial_page);
+			unlock_buffer(bh);
+			if (ret < 0)
+				return ret;
+			may_free &= ret;
+		}
+		curr_off = next_off;
+		bh = next;
+
+	} while (bh != head);
+
+	if (!partial_page) {
+		if (may_free && try_to_free_buffers(page))
+			J_ASSERT(!page_has_buffers(page));
+	}
+	return 0;
+}
+
+/*
+ * 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_Shadow:
+		list = &transaction->t_shadow_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;
+
+	if (is_handle_aborted(handle))
+		return -EROFS;
+	journal = transaction->t_journal;
+
+	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;
+}