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+ jbd-fix-race-in-buffer-processing-in-commit-code.patch added to -mm tree

Message ID 200906082258.n58MwtDI020940@imap1.linux-foundation.org
State Not Applicable, archived
Headers show

Commit Message

Andrew Morton June 8, 2009, 10:58 p.m. UTC
The patch titled
     jbd: fix race in buffer processing in commit code
has been added to the -mm tree.  Its filename is

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Subject: jbd: fix race in buffer processing in commit code
From: Jan Kara <jack@suse.cz>

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 <jack@suse.cz>
Cc: <stable@kernel.org>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 fs/jbd/commit.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
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diff -puN fs/jbd/commit.c~jbd-fix-race-in-buffer-processing-in-commit-code fs/jbd/commit.c
--- a/fs/jbd/commit.c~jbd-fix-race-in-buffer-processing-in-commit-code
+++ a/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_
-		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) {