From: Jan Kara <jack@suse.cz>
Date: Tue, 9 Jun 2009 23:26:26 +0000 (-0700)
Subject: jbd: fix race in buffer processing in commit code
X-Git-Tag: v2.6.30~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a61d90d75d0f9e86432c45b496b4b0fbf0fd03dc;p=pandora-kernel.git

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
list.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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