diff options
| author | Miklos Szeredi <miklos@szeredi.hu> | 2012-09-17 22:23:30 +0200 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2012-10-10 03:31:13 +0100 |
| commit | 5e47beb778ad1c5fa901a61700f3ac1b4ee8a579 (patch) | |
| tree | e3764f75a5db39ff708b33bf075d1451b01746d6 /fs/dcache.c | |
| parent | b4723adc0c336e153b6396f8c0e3f396cd9e9b5d (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: Ben Hutchings <ben@decadent.org.uk>
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 d20dc2b700c..63c0c6b9b82 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1054,6 +1054,8 @@ positive: return 1; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -1156,6 +1158,8 @@ out: rename_retry: if (found) return found; + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -2922,6 +2926,8 @@ resume: return; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; |