From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754588AbdL1RO0 (ORCPT ); Thu, 28 Dec 2017 12:14:26 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:59095 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754406AbdL1ROE (ORCPT ); Thu, 28 Dec 2017 12:14:04 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "syzbot" , "Dmitry Vyukov" , "Takashi Iwai" Date: Thu, 28 Dec 2017 17:05:44 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 153/204] ALSA: seq: Fix nested rwsem annotation for lockdep splat In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 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 3.16.52-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit 1f20f9ff57ca23b9f5502fca85ce3977e8496cb1 upstream. syzkaller reported the lockdep splat due to the possible deadlock of grp->list_mutex of each sequencer client object. Actually this is rather a false-positive report due to the missing nested lock annotations. The sequencer client may deliver the event directly to another client which takes another own lock. For addressing this issue, this patch replaces the simple down_read() with down_read_nested(). As a lock subclass, the already existing "hop" can be re-used, which indicates the depth of the call. Reference: http://lkml.kernel.org/r/089e082686ac9b482e055c832617@google.com Reported-by: syzbot Reported-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Ben Hutchings --- sound/core/seq/seq_clientmgr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -676,7 +676,7 @@ static int deliver_to_subscribers(struct if (atomic) read_lock(&grp->list_lock); else - down_read(&grp->list_mutex); + down_read_nested(&grp->list_mutex, hop); list_for_each_entry(subs, &grp->list_head, src_list) { /* both ports ready? */ if (atomic_read(&subs->ref_count) != 2)