commit: 8110e16d42d587997bcaee0c864179e6d93603fe
From: Miklos Szeredi <[email protected]>
Date: Mon, 17 Sep 2012 22:23:30 +0200
Subject: vfs: dcache: fix deadlock in tree traversal
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]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>
---
fs/dcache.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 0364af2..693f95b 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1134,6 +1134,8 @@ positive:
return 1;
rename_retry:
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
@@ -1236,6 +1238,8 @@ out:
rename_retry:
if (found)
return found;
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
@@ -3035,6 +3039,8 @@ resume:
return;
rename_retry:
+ if (locked)
+ goto again;
locked = 1;
write_seqlock(&rename_lock);
goto again;
--
1.7.3.4
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