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Date:	Mon,  8 Jun 2009 19:21:46 +0200
From:	Jan Kara <>
Cc:	Andrew Morton <>,,
	Jan Kara <>
Subject: [PATCH] jbd: Fix race in buffer processing in commit code

In commit code, we scan buffers attached to a transaction. During this
scan, we sometimes have to drop j_list_lock and then we recheck whether
the journal buffer head didn't get freed by journal_try_to_free_buffers().
But checking for buffer_jbd(bh) isn't enough because a new journal head
could get attached to our buffer head. So add a check whether the journal
head remained the same and whether it's still at the same transaction and

This is a nasty bug and can cause problems like memory corruption (use after
free) or trigger various assertions in JBD code (observed).

Signed-off-by: Jan Kara <>
 fs/jbd/commit.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

 Andrew, would you please merge it? Thanks. BTW, JBD2 does not have the problem
since we handle ordered mode data buffers differently there.

diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 06560c5..618e21c 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -241,7 +241,7 @@ write_out_data:
 		/* Someone already cleaned up the buffer? */
-		if (!buffer_jbd(bh)
+		if (!buffer_jbd(bh) || bh2jh(bh) != jh
 			|| jh->b_transaction != commit_transaction
 			|| jh->b_jlist != BJ_SyncData) {
@@ -478,7 +478,9 @@ void journal_commit_transaction(journal_t *journal)
-		if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
+		if (buffer_jbd(bh) && bh2jh(bh) == jh &&
+		    jh->b_transaction == commit_transaction &&
+		    jh->b_jlist == BJ_Locked) {

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