This is a note to let you know that I've just added the patch titled
vfs: dcache: fix deadlock in tree traversal
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
vfs-dcache-fix-deadlock-in-tree-traversal.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 8110e16d42d587997bcaee0c864179e6d93603fe Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <[email protected]>
Date: Mon, 17 Sep 2012 22:23:30 +0200
Subject: vfs: dcache: fix deadlock in tree traversal
From: Miklos Szeredi <[email protected]>
commit 8110e16d42d587997bcaee0c864179e6d93603fe upstream.
IBM reported a deadlock in select_parent(). This was found to be caused
by taking rename_lock when already locked when restarting the tree
traversal.
There are two cases when the traversal needs to be restarted:
1) concurrent d_move(); this can only happen when not already locked,
since taking rename_lock protects against concurrent d_move().
2) racing with final d_put() on child just at the moment of ascending
to parent; rename_lock doesn't protect against this rare race, so it
can happen when already locked.
Because of case 2, we need to be able to handle restarting the traversal
when rename_lock is already held. This patch fixes all three callers of
try_to_ascend().
IBM reported that the deadlock is gone with this patch.
[ I rewrote the patch to be smaller and just do the "goto again" if the
lock was already held, but credit goes to Miklos for the real work.
- Linus ]
Signed-off-by: Miklos Szeredi <[email protected]>
Cc: Al Viro <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/dcache.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1116,6 +1116,8 @@ positive:
return 1;
rename_retry:
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
@@ -1218,6 +1220,8 @@ out:
rename_retry:
if (found)
return found;
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
@@ -2963,6 +2967,8 @@ resume:
return;
rename_retry:
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/vfs-dcache-fix-deadlock-in-tree-traversal.patch
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