diff options
| author | Miklos Szeredi <miklos@szeredi.hu> | 2012-09-17 22:23:30 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-10-07 08:27:23 -0700 |
| commit | d2212d278786f0e0a1942796c7e5549a49fa5b34 (patch) | |
| tree | 2ce77190e09bdca1895a5a4aab907482011e600e /fs/dcache.c | |
| parent | b9a7985a8d9ca00d8ce977756fde1306c9ab1e41 (diff) | |
vfs: dcache: fix deadlock in tree traversal
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 <mszeredi@suse.cz>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/dcache.c')
| -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 bd8aaf66140..8b64f383570 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1101,6 +1101,8 @@ positive: return 1; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -1203,6 +1205,8 @@ out: rename_retry: if (found) return found; + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -2990,6 +2994,8 @@ resume: return; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; |