Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754617Ab2JGXXP (ORCPT ); Sun, 7 Oct 2012 19:23:15 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:38490 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754290Ab2JGXWs (ORCPT ); Sun, 7 Oct 2012 19:22:48 -0400 Message-Id: <20121007225843.414964653@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Sun, 07 Oct 2012 23:59:37 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Miklos Szeredi , Miklos Szeredi , Al Viro , Linus Torvalds Subject: [ 063/108] vfs: dcache: fix deadlock in tree traversal In-Reply-To: <20121007225834.673681075@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2181 Lines: 77 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Miklos Szeredi 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 Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- fs/dcache.c | 6 ++++++ 1 file changed, 6 insertions(+) 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/