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Date:	Mon, 08 Jun 2009 15:58:55 -0700
From:	akpm@...ux-foundation.org
To:	mm-commits@...r.kernel.org
Cc:	jack@...e.cz, linux-ext4@...r.kernel.org, stable@...nel.org
Subject: + jbd-fix-race-in-buffer-processing-in-commit-code.patch added to -mm tree


The patch titled
     jbd: fix race in buffer processing in commit code
has been added to the -mm tree.  Its filename is
     jbd-fix-race-in-buffer-processing-in-commit-code.patch

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   a) Consider who else should be cc'ed
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*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this

The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/

------------------------------------------------------
Subject: jbd: fix race in buffer processing in commit code
From: Jan Kara <jack@...e.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
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@...e.cz>
Cc: <stable@...nel.org>
Cc: <linux-ext4@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 fs/jbd/commit.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

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:
 			spin_lock(&journal->j_list_lock);
 		}
 		/* 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) {
 			jbd_unlock_bh_state(bh);
@@ -478,7 +478,9 @@ void journal_commit_transaction(journal_
 			spin_lock(&journal->j_list_lock);
 			continue;
 		}
-		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) {
 			__journal_unfile_buffer(jh);
 			jbd_unlock_bh_state(bh);
 			journal_remove_journal_head(bh);
_

Patches currently in -mm which might be from jack@...e.cz are

jbd-fix-race-in-buffer-processing-in-commit-code.patch
linux-next.patch
vfs-split-generic_forget_inode-so-that-hugetlbfs-does-not-have-to-copy-it.patch
ext2-add-blk_issue_flush-to-syncing-paths.patch
mm-remove-__invalidate_mapping_pages-variant.patch
ext2-do-not-update-mtime-of-a-moved-directory.patch
ext3-fix-chain-verification-in-ext3_get_blocks.patch
isofs-let-mode-and-dmode-mount-options-override-rock-ridge-mode-setting.patch
isofs-fix-setting-of-uid-and-gid-to-0.patch
isofs-cleanup-mount-option-processing.patch
reiser4-update-names-of-quota-methods.patch

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