Patchwork jbd2: Fix oops in jbd2_journal_remove_journal_head()

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Submitter Jan Kara
Date May 30, 2011, 3:12 p.m.
Message ID <1306768378-27748-1-git-send-email-jack@suse.cz>
Download mbox | patch
Permalink /patch/97926/
State Superseded
Headers show

Comments

Jan Kara - May 30, 2011, 3:12 p.m.
jbd2_journal_remove_journal_head() can oops when trying to access
journal_head returned by bh2jh(). This is caused for example by the
following race:
	TASK1					TASK2
  jbd2_journal_commit_transaction()
    ...
    processing t_forget list
      __jbd2_journal_refile_buffer(jh);
      if (!jh->b_transaction) {
        jbd_unlock_bh_state(bh);
					jbd2_journal_try_to_free_buffers()
					  jbd2_journal_grab_journal_head(bh)
					  jbd_lock_bh_state(bh)
					  __journal_try_to_free_buffer()
					  jbd2_journal_put_journal_head(jh)
        jbd2_journal_remove_journal_head(bh);

jbd2_journal_put_journal_head() in TASK2 sees that b_jcount == 0 and buffer
is not part of any transaction and thus frees journal_head before TASK1 gets
to doing so. Note that even buffer_head can be released by
try_to_free_buffers() after jbd2_journal_put_journal_head() which adds even
larger opportunity for oops (but I didn't see this happen in reality).

Fix the problem by making transactions hold their own journal_head reference
(in b_jcount). That way we don't have to remove journal_head explicitely via
jbd2_journal_remove_journal_head() and instead just remove journal_head when
b_jcount drops to zero. The result of this is that
[__]jbd2_journal_refile_buffer(), [__]jbd2_journal_unfile_buffer(), and
__jdb2_journal_remove_checkpoint() can free journal_head which needs
modification of a few callers. Also we have to be careful because once
journal_head is removed, buffer_head might be freed as well. So we have to get
our own buffer_head reference where it matters.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/jbd2/checkpoint.c  |   25 +++++++------
 fs/jbd2/commit.c      |   33 ++++++++++-------
 fs/jbd2/journal.c     |   94 +++++++++++++++++--------------------------------
 fs/jbd2/transaction.c |   70 +++++++++++++++++++++---------------
 include/linux/jbd2.h  |    2 -
 5 files changed, 105 insertions(+), 119 deletions(-)

 This has survived some testing but really it would use another pair of
eyes in review since if there are bugs, they would be hard to trigger. The
logic should not be hard to follow, there are just quite a few places that
need to be updated...

PS: Alternative, less intrusive fix would be to make
jbd2_journal_remove_journal_head() tolerate NULL journal_head (I might go this
route for JBD) but it really seems just cleaner for transactions to hold their
references when they really reference the journal_head...
Theodore Ts'o - June 6, 2011, 2:16 p.m.
On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
>  /*
> - * For the unlocked version of this call, also make sure that any
> - * hanging journal_head is cleaned up if necessary.
> + * For the unlocked version of this call, also drop buffer_head reference.
>   *
>   * __jbd2_journal_refile_buffer is usually called as part of a single locked
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
__jbd2_journal_refile_buffer()?  Or am I missing something?

>  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);

OK, so we're adding a get_bh(bh) call to jbd2_journal_refile_buffer(),
which we're not freeing later in the function.  So this means every
single place where we call jbd2_journal_refile_buffer(), we'd better
add put_bh(bh) or bhrelse(bh) call, right?

So in fs/jbd2/commit.c, line 418, in jbd2_journal_commit_transaction(),
I see a call to jbd2_journal_refile_buffer(), which the patch doesn't
seem to adjust.  Looks like this could cause a buffer leak?

In your testing, have you checked to the slab cache to make sure there
isn't any memory leakage going on with buffer heads?

      	  	 	       	       - Ted
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Theodore Ts'o - June 8, 2011, 2:09 p.m.
Ping?

				- Ted

On Mon, Jun 06, 2011 at 10:16:30AM -0400, Ted Ts'o wrote:
> On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
> >  /*
> > - * For the unlocked version of this call, also make sure that any
> > - * hanging journal_head is cleaned up if necessary.
> > + * For the unlocked version of this call, also drop buffer_head reference.
> >   *
> >   * __jbd2_journal_refile_buffer is usually called as part of a single locked
>      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
> __jbd2_journal_refile_buffer()?  Or am I missing something?
> 
> >  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);
> 
> OK, so we're adding a get_bh(bh) call to jbd2_journal_refile_buffer(),
> which we're not freeing later in the function.  So this means every
> single place where we call jbd2_journal_refile_buffer(), we'd better
> add put_bh(bh) or bhrelse(bh) call, right?
> 
> So in fs/jbd2/commit.c, line 418, in jbd2_journal_commit_transaction(),
> I see a call to jbd2_journal_refile_buffer(), which the patch doesn't
> seem to adjust.  Looks like this could cause a buffer leak?
> 
> In your testing, have you checked to the slab cache to make sure there
> isn't any memory leakage going on with buffer heads?
> 
>       	  	 	       	       - Ted
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Jan Kara - June 8, 2011, 7:31 p.m.
On Mon 06-06-11 10:16:30, Ted Tso wrote:
> On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
> >  /*
> > - * For the unlocked version of this call, also make sure that any
> > - * hanging journal_head is cleaned up if necessary.
> > + * For the unlocked version of this call, also drop buffer_head reference.
> >   *
> >   * __jbd2_journal_refile_buffer is usually called as part of a single locked
>      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
> __jbd2_journal_refile_buffer()?  Or am I missing something?
  Hmm, the comment seems to be wrong. The comment about buffer_head
reference does not apply anymore. I'll fix that.

> >  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);
> 
> OK, so we're adding a get_bh(bh) call to jbd2_journal_refile_buffer(),
> which we're not freeing later in the function.  So this means every
> single place where we call jbd2_journal_refile_buffer(), we'd better
> add put_bh(bh) or bhrelse(bh) call, right?
Well, we are adding get_bh() but we are now also using
jbd2_journal_put_journal_head() instead of
jbd2_journal_remove_journal_head() and the former call does additional
__brelse().

Probably a better way to look at this is that
jbd2_journal_remove_journal_head() now gets a reference and puts it at the
end of that function. jbd2_journal_put_journal_head() cares about releasing
bh reference held by journal_head. So the logic ends up being simpler than
it used to be.

> So in fs/jbd2/commit.c, line 418, in jbd2_journal_commit_transaction(),
> I see a call to jbd2_journal_refile_buffer(), which the patch doesn't
> seem to adjust.  Looks like this could cause a buffer leak?
> 
> In your testing, have you checked to the slab cache to make sure there
> isn't any memory leakage going on with buffer heads?
  Not really - I now ran fsxlinux and fsstress and both the number of
buffer_head and journal_head slabs seem to be under control.

								Honza
Theodore Ts'o - June 12, 2011, 9:41 p.m.
On Wed, Jun 08, 2011 at 09:31:42PM +0200, Jan Kara wrote:
> On Mon 06-06-11 10:16:30, Ted Tso wrote:
> > On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
> > >  /*
> > > - * For the unlocked version of this call, also make sure that any
> > > - * hanging journal_head is cleaned up if necessary.
> > > + * For the unlocked version of this call, also drop buffer_head reference.
> > >   *
> > >   * __jbd2_journal_refile_buffer is usually called as part of a single locked
> >      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 
> > Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
> > __jbd2_journal_refile_buffer()?  Or am I missing something?
>   Hmm, the comment seems to be wrong. The comment about buffer_head
> reference does not apply anymore. I'll fix that.


Are you going to be sending me a new version of this patch with this
comment fixed?  Or should I just remove it?

Thanks,

						- Ted
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Jan Kara - June 13, 2011, 2:10 p.m.
On Sun 12-06-11 17:41:13, Ted Tso wrote:
> On Wed, Jun 08, 2011 at 09:31:42PM +0200, Jan Kara wrote:
> > On Mon 06-06-11 10:16:30, Ted Tso wrote:
> > > On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
> > > >  /*
> > > > - * For the unlocked version of this call, also make sure that any
> > > > - * hanging journal_head is cleaned up if necessary.
> > > > + * For the unlocked version of this call, also drop buffer_head reference.
> > > >   *
> > > >   * __jbd2_journal_refile_buffer is usually called as part of a single locked
> > >      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > 
> > > Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
> > > __jbd2_journal_refile_buffer()?  Or am I missing something?
> >   Hmm, the comment seems to be wrong. The comment about buffer_head
> > reference does not apply anymore. I'll fix that.
> 
> Are you going to be sending me a new version of this patch with this
> comment fixed?  Or should I just remove it?
  I've replaced a comment with a better one, also fixed one more wrong
comment I've found and resent the patch now. Thanks for reminding me.

								Honza

Patch

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 3436d53..b14a53d 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -97,10 +97,14 @@  static int __try_to_free_cp_buf(struct journal_head *jh)
 
 	if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
 	    !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
+		/*
+		 * Get our reference so that bh cannot be freed before
+		 * we unlock it
+		 */
+		get_bh(bh);
 		JBUFFER_TRACE(jh, "remove from checkpoint list");
 		ret = __jbd2_journal_remove_checkpoint(jh) + 1;
 		jbd_unlock_bh_state(bh);
-		jbd2_journal_remove_journal_head(bh);
 		BUFFER_TRACE(bh, "release");
 		__brelse(bh);
 	} else {
@@ -223,8 +227,8 @@  restart:
 			spin_lock(&journal->j_list_lock);
 			goto restart;
 		}
+		get_bh(bh);
 		if (buffer_locked(bh)) {
-			atomic_inc(&bh->b_count);
 			spin_unlock(&journal->j_list_lock);
 			jbd_unlock_bh_state(bh);
 			wait_on_buffer(bh);
@@ -243,7 +247,6 @@  restart:
 		 */
 		released = __jbd2_journal_remove_checkpoint(jh);
 		jbd_unlock_bh_state(bh);
-		jbd2_journal_remove_journal_head(bh);
 		__brelse(bh);
 	}
 
@@ -284,7 +287,7 @@  static int __process_buffer(journal_t *journal, struct journal_head *jh,
 	int ret = 0;
 
 	if (buffer_locked(bh)) {
-		atomic_inc(&bh->b_count);
+		get_bh(bh);
 		spin_unlock(&journal->j_list_lock);
 		jbd_unlock_bh_state(bh);
 		wait_on_buffer(bh);
@@ -316,12 +319,12 @@  static int __process_buffer(journal_t *journal, struct journal_head *jh,
 		ret = 1;
 		if (unlikely(buffer_write_io_error(bh)))
 			ret = -EIO;
+		get_bh(bh);
 		J_ASSERT_JH(jh, !buffer_jbddirty(bh));
 		BUFFER_TRACE(bh, "remove from checkpoint");
 		__jbd2_journal_remove_checkpoint(jh);
 		spin_unlock(&journal->j_list_lock);
 		jbd_unlock_bh_state(bh);
-		jbd2_journal_remove_journal_head(bh);
 		__brelse(bh);
 	} else {
 		/*
@@ -663,8 +666,8 @@  out:
  * checkpoint lists.
  *
  * The function returns 1 if it frees the transaction, 0 otherwise.
+ * The function can free jh and bh.
  *
- * This function is called with the journal locked.
  * This function is called with j_list_lock held.
  * This function is called with jbd_lock_bh_state(jh2bh(jh))
  */
@@ -684,13 +687,14 @@  int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 	}
 	journal = transaction->t_journal;
 
+	JBUFFER_TRACE(jh, "removing from transaction");
 	__buffer_unlink(jh);
 	jh->b_cp_transaction = NULL;
+	jbd2_journal_put_journal_head(jh);
 
 	if (transaction->t_checkpoint_list != NULL ||
 	    transaction->t_checkpoint_io_list != NULL)
 		goto out;
-	JBUFFER_TRACE(jh, "transaction has no more buffers");
 
 	/*
 	 * There is one special case to worry about: if we have just pulled the
@@ -701,10 +705,8 @@  int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 	 * The locking here around t_state is a bit sleazy.
 	 * See the comment at the end of jbd2_journal_commit_transaction().
 	 */
-	if (transaction->t_state != T_FINISHED) {
-		JBUFFER_TRACE(jh, "belongs to running/committing transaction");
+	if (transaction->t_state != T_FINISHED)
 		goto out;
-	}
 
 	/* OK, that was the last buffer for the transaction: we can now
 	   safely remove this transaction from the log */
@@ -723,7 +725,6 @@  int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 	wake_up(&journal->j_wait_logspace);
 	ret = 1;
 out:
-	JBUFFER_TRACE(jh, "exit");
 	return ret;
 }
 
@@ -742,6 +743,8 @@  void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
 	J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 	J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 
+	/* Get reference for checkpointing transaction */
+	jbd2_journal_grab_journal_head(jh2bh(jh));
 	jh->b_cp_transaction = transaction;
 
 	if (!transaction->t_checkpoint_list) {
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 6dd6515..4b2f482 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -856,10 +856,16 @@  restart_loop:
 	while (commit_transaction->t_forget) {
 		transaction_t *cp_transaction;
 		struct buffer_head *bh;
+		int try_to_free = 0;
 
 		jh = commit_transaction->t_forget;
 		spin_unlock(&journal->j_list_lock);
 		bh = jh2bh(jh);
+		/*
+		 * Get a reference so that bh cannot be freed before we are
+		 * done with it.
+		 */
+		get_bh(bh);
 		jbd_lock_bh_state(bh);
 		J_ASSERT_JH(jh,	jh->b_transaction == commit_transaction);
 
@@ -922,28 +928,27 @@  restart_loop:
 			__jbd2_journal_insert_checkpoint(jh, commit_transaction);
 			if (is_journal_aborted(journal))
 				clear_buffer_jbddirty(bh);
-			JBUFFER_TRACE(jh, "refile for checkpoint writeback");
-			__jbd2_journal_refile_buffer(jh);
-			jbd_unlock_bh_state(bh);
 		} else {
 			J_ASSERT_BH(bh, !buffer_dirty(bh));
-			/* The buffer on BJ_Forget list and not jbddirty means
+			/*
+			 * The buffer on BJ_Forget list and not jbddirty means
 			 * it has been freed by this transaction and hence it
 			 * could not have been reallocated until this
 			 * transaction has committed. *BUT* it could be
 			 * reallocated once we have written all the data to
 			 * disk and before we process the buffer on BJ_Forget
-			 * list. */
-			JBUFFER_TRACE(jh, "refile or unfile freed buffer");
-			__jbd2_journal_refile_buffer(jh);
-			if (!jh->b_transaction) {
-				jbd_unlock_bh_state(bh);
-				 /* needs a brelse */
-				jbd2_journal_remove_journal_head(bh);
-				release_buffer_page(bh);
-			} else
-				jbd_unlock_bh_state(bh);
+			 * list.
+			 */
+			if (!jh->b_next_transaction)
+				try_to_free = 1;
 		}
+		JBUFFER_TRACE(jh, "refile or unfile buffer");
+		__jbd2_journal_refile_buffer(jh);
+		jbd_unlock_bh_state(bh);
+		if (try_to_free)
+			release_buffer_page(bh);	/* Drops bh reference */
+		else
+			__brelse(bh);
 		cond_resched_lock(&journal->j_list_lock);
 	}
 	spin_unlock(&journal->j_list_lock);
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 728f7d3..ce1c76d 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -2079,10 +2079,9 @@  static void journal_free_journal_head(struct journal_head *jh)
  * When a buffer has its BH_JBD bit set it is immune from being released by
  * core kernel code, mainly via ->b_count.
  *
- * A journal_head may be detached from its buffer_head when the journal_head's
- * b_transaction, b_cp_transaction and b_next_transaction pointers are NULL.
- * Various places in JBD call jbd2_journal_remove_journal_head() to indicate that the
- * journal_head can be dropped if needed.
+ * A journal_head is detached from its buffer_head when the journal_head's
+ * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
+ * transaction (b_cp_transaction) hold their references to b_jcount.
  *
  * Various places in the kernel want to attach a journal_head to a buffer_head
  * _before_ attaching the journal_head to a transaction.  To protect the
@@ -2095,17 +2094,16 @@  static void journal_free_journal_head(struct journal_head *jh)
  *	(Attach a journal_head if needed.  Increments b_jcount)
  *	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
  *	...
+ *      (Get another reference for transaction)
+ *	jbd2_journal_grab_journal_head(bh);
  *	jh->b_transaction = xxx;
+ *	(Put original reference)
  *	jbd2_journal_put_journal_head(jh);
- *
- * Now, the journal_head's b_jcount is zero, but it is safe from being released
- * because it has a non-zero b_transaction.
  */
 
 /*
  * Give a buffer_head a journal_head.
  *
- * Doesn't need the journal lock.
  * May sleep.
  */
 struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh)
@@ -2169,62 +2167,33 @@  static void __journal_remove_journal_head(struct buffer_head *bh)
 	struct journal_head *jh = bh2jh(bh);
 
 	J_ASSERT_JH(jh, jh->b_jcount >= 0);
-
-	get_bh(bh);
-	if (jh->b_jcount == 0) {
-		if (jh->b_transaction == NULL &&
-				jh->b_next_transaction == NULL &&
-				jh->b_cp_transaction == NULL) {
-			J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
-			J_ASSERT_BH(bh, buffer_jbd(bh));
-			J_ASSERT_BH(bh, jh2bh(jh) == bh);
-			BUFFER_TRACE(bh, "remove journal_head");
-			if (jh->b_frozen_data) {
-				printk(KERN_WARNING "%s: freeing "
-						"b_frozen_data\n",
-						__func__);
-				jbd2_free(jh->b_frozen_data, bh->b_size);
-			}
-			if (jh->b_committed_data) {
-				printk(KERN_WARNING "%s: freeing "
-						"b_committed_data\n",
-						__func__);
-				jbd2_free(jh->b_committed_data, bh->b_size);
-			}
-			bh->b_private = NULL;
-			jh->b_bh = NULL;	/* debug, really */
-			clear_buffer_jbd(bh);
-			__brelse(bh);
-			journal_free_journal_head(jh);
-		} else {
-			BUFFER_TRACE(bh, "journal_head was locked");
-		}
+	J_ASSERT_JH(jh, jh->b_transaction == NULL);
+	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+	J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
+	J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
+	J_ASSERT_BH(bh, buffer_jbd(bh));
+	J_ASSERT_BH(bh, jh2bh(jh) == bh);
+	BUFFER_TRACE(bh, "remove journal_head");
+	if (jh->b_frozen_data) {
+		printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
+		jbd2_free(jh->b_frozen_data, bh->b_size);
 	}
+	if (jh->b_committed_data) {
+		printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
+		jbd2_free(jh->b_committed_data, bh->b_size);
+	}
+	bh->b_private = NULL;
+	jh->b_bh = NULL;	/* debug, really */
+	clear_buffer_jbd(bh);
+	journal_free_journal_head(jh);
 }
 
 /*
- * jbd2_journal_remove_journal_head(): if the buffer isn't attached to a transaction
- * and has a zero b_jcount then remove and release its journal_head.   If we did
- * see that the buffer is not used by any transaction we also "logically"
- * decrement ->b_count.
- *
- * We in fact take an additional increment on ->b_count as a convenience,
- * because the caller usually wants to do additional things with the bh
- * after calling here.
- * The caller of jbd2_journal_remove_journal_head() *must* run __brelse(bh) at some
- * time.  Once the caller has run __brelse(), the buffer is eligible for
- * reaping by try_to_free_buffers().
- */
-void jbd2_journal_remove_journal_head(struct buffer_head *bh)
-{
-	jbd_lock_bh_journal_head(bh);
-	__journal_remove_journal_head(bh);
-	jbd_unlock_bh_journal_head(bh);
-}
-
-/*
- * Drop a reference on the passed journal_head.  If it fell to zero then try to
+ * Drop a reference on the passed journal_head.  If it fell to zero then
  * release the journal_head from the buffer_head.
+ *
+ * Returns 1 if journal_head was released and in such case return with
+ * buffer_head reference that must be released by the caller.
  */
 void jbd2_journal_put_journal_head(struct journal_head *jh)
 {
@@ -2233,11 +2202,12 @@  void jbd2_journal_put_journal_head(struct journal_head *jh)
 	jbd_lock_bh_journal_head(bh);
 	J_ASSERT_JH(jh, jh->b_jcount > 0);
 	--jh->b_jcount;
-	if (!jh->b_jcount && !jh->b_transaction) {
+	if (!jh->b_jcount) {
 		__journal_remove_journal_head(bh);
+		jbd_unlock_bh_journal_head(bh);
 		__brelse(bh);
-	}
-	jbd_unlock_bh_journal_head(bh);
+	} else
+		jbd_unlock_bh_journal_head(bh);
 }
 
 /*
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 49646cc..b26bd21 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -30,6 +30,7 @@ 
 #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.
@@ -764,7 +765,6 @@  repeat:
 	if (!jh->b_transaction) {
 		JBUFFER_TRACE(jh, "no transaction");
 		J_ASSERT_JH(jh, !jh->b_next_transaction);
-		jh->b_transaction = transaction;
 		JBUFFER_TRACE(jh, "file as BJ_Reserved");
 		spin_lock(&journal->j_list_lock);
 		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
@@ -896,8 +896,6 @@  int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
 		 * committed and so it's safe to clear the dirty bit.
 		 */
 		clear_buffer_dirty(jh2bh(jh));
-		jh->b_transaction = transaction;
-
 		/* first access by this transaction */
 		jh->b_modified = 0;
 
@@ -1232,8 +1230,6 @@  int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
 			__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
 		} else {
 			__jbd2_journal_unfile_buffer(jh);
-			jbd2_journal_remove_journal_head(bh);
-			__brelse(bh);
 			if (!buffer_jbd(bh)) {
 				spin_unlock(&journal->j_list_lock);
 				jbd_unlock_bh_state(bh);
@@ -1555,19 +1551,32 @@  void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
 		mark_buffer_dirty(bh);	/* Expose it to the VM */
 }
 
-void __jbd2_journal_unfile_buffer(struct journal_head *jh)
+/*
+ * 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)
 {
-	jbd_lock_bh_state(jh2bh(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(jh2bh(jh));
+	jbd_unlock_bh_state(bh);
+	__brelse(bh);
 }
 
 /*
@@ -1594,8 +1603,6 @@  __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
 		if (jh->b_jlist == BJ_None) {
 			JBUFFER_TRACE(jh, "remove from checkpoint list");
 			__jbd2_journal_remove_checkpoint(jh);
-			jbd2_journal_remove_journal_head(bh);
-			__brelse(bh);
 		}
 	}
 	spin_unlock(&journal->j_list_lock);
@@ -1658,7 +1665,6 @@  int jbd2_journal_try_to_free_buffers(journal_t *journal,
 		/*
 		 * We take our own ref against the journal_head here to avoid
 		 * having to add tons of locking around each instance of
-		 * jbd2_journal_remove_journal_head() and
 		 * jbd2_journal_put_journal_head().
 		 */
 		jh = jbd2_journal_grab_journal_head(bh);
@@ -1696,10 +1702,9 @@  static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
 	int may_free = 1;
 	struct buffer_head *bh = jh2bh(jh);
 
-	__jbd2_journal_unfile_buffer(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
@@ -1710,8 +1715,7 @@  static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
 		may_free = 0;
 	} else {
 		JBUFFER_TRACE(jh, "on running transaction");
-		jbd2_journal_remove_journal_head(bh);
-		__brelse(bh);
+		__jbd2_journal_unfile_buffer(jh);
 	}
 	return may_free;
 }
@@ -1989,6 +1993,8 @@  void __jbd2_journal_file_buffer(struct journal_head *jh,
 
 	if (jh->b_transaction)
 		__jbd2_journal_temp_unlink_buffer(jh);
+	else
+		jbd2_journal_grab_journal_head(bh);
 	jh->b_transaction = transaction;
 
 	switch (jlist) {
@@ -2040,9 +2046,10 @@  void jbd2_journal_file_buffer(struct journal_head *jh,
  * already started to be used by a subsequent transaction, refile the
  * buffer on that transaction's metadata list.
  *
- * Called under journal->j_list_lock
- *
+ * 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)
 {
@@ -2066,6 +2073,11 @@  void __jbd2_journal_refile_buffer(struct journal_head *jh)
 
 	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))
@@ -2082,30 +2094,28 @@  void __jbd2_journal_refile_buffer(struct journal_head *jh)
 }
 
 /*
- * For the unlocked version of this call, also make sure that any
- * hanging journal_head is cleaned up if necessary.
+ * For the unlocked version of this call, also drop buffer_head reference.
  *
  * __jbd2_journal_refile_buffer is usually called as part of a single locked
- * operation on a buffer_head, in which the caller is probably going to
- * be hooking the journal_head onto other lists.  In that case it is up
- * to the caller to remove the journal_head if necessary.  For the
- * unlocked jbd2_journal_refile_buffer call, the caller isn't going to be
- * doing anything else to the buffer so we need to do the cleanup
- * ourselves to avoid a jh leak.
- *
- * *** The journal_head may be freed by this call! ***
+ * operation on a buffer_head, in which the caller is probably going to use
+ * buffer_head further (at least for jbd_unlock_bh_state).  In that case it is
+ * up to the caller to drop buffer_head reference. For the unlocked
+ * jbd2_journal_refile_buffer call, the caller isn't going to be doing anything
+ * else to the buffer so we need to do the cleanup ourselves to avoid a bh
+ * leak.
+ *
+ * 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);
-	jbd2_journal_remove_journal_head(bh);
-
 	spin_unlock(&journal->j_list_lock);
 	__brelse(bh);
 }
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 309cc49..54eb7f9 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1027,7 +1027,6 @@  struct journal_s
 
 /* Filing buffers */
 extern void jbd2_journal_unfile_buffer(journal_t *, struct journal_head *);
-extern void __jbd2_journal_unfile_buffer(struct journal_head *);
 extern void __jbd2_journal_refile_buffer(struct journal_head *);
 extern void jbd2_journal_refile_buffer(journal_t *, struct journal_head *);
 extern void __jbd2_journal_file_buffer(struct journal_head *, transaction_t *, int);
@@ -1168,7 +1167,6 @@  extern void	   jbd2_journal_release_jbd_inode(journal_t *journal, struct jbd2_in
  */
 struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh);
 struct journal_head *jbd2_journal_grab_journal_head(struct buffer_head *bh);
-void jbd2_journal_remove_journal_head(struct buffer_head *bh);
 void jbd2_journal_put_journal_head(struct journal_head *jh);
 
 /*