diff options
| author | Miklos Szeredi <miklos@szeredi.hu> | 2012-09-17 22:23:30 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-09-29 17:41:40 -0700 |
| commit | 8110e16d42d587997bcaee0c864179e6d93603fe (patch) | |
| tree | 210b83419cc6464b1a1faff58c47d8316f6e5939 | |
| parent | 6a3e3dbee62a8fcf13c349b141b3cedf35a65c41 (diff) | |
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 <mszeredi@suse.cz>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/dcache.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 0364af2311f..693f95bf1ca 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; |