From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Lawrence Subject: bug: race in team_{notify_peers,mcast_rejoin} scheduling Date: Thu, 2 Oct 2014 14:50:28 -0400 Message-ID: <20141002145028.2f62838c@jlaw-desktop.mno.stratus.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 8BIT To: , Jiri Pirko Return-path: Received: from p02c12o148.mxlogic.net ([208.65.145.81]:58278 "EHLO p02c12o148.mxlogic.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751357AbaJBSuh convert rfc822-to-8bit (ORCPT ); Thu, 2 Oct 2014 14:50:37 -0400 Sender: netdev-owner@vger.kernel.org List-ID: Hello Jiri, Occasionally on boot I noticed that team_notify_peers_work would get *very* busy. With the following debugging added to team_notify_peers: netdev_info(team->dev, "%s(%p)\n", __func__, team); dump_stack(); I saw the following: % dmesg | grep -e 'team[0-9]: team_notify_peers' -e 'port_enable' -e 'port_disable' [ 68.340861] team0: team_notify_peers(ffff88104ffa4de0) [ 68.743264] [] team_port_enable.part.40+0x78/0x90 [team] [ 69.622395] team0: team_notify_peers(ffff88104ffa4de0) [ 69.966758] [] team_port_disable+0x123/0x160 [team] [ 71.099263] team0: team_notify_peers(ffff88104ffa4de0) [ 71.466243] [] team_port_enable.part.40+0x78/0x90 [team] [ 72.383788] team0: team_notify_peers(ffff88104ffa4de0) [ 72.744778] [] team_port_disable+0x123/0x160 [team] [ 73.476190] team0: team_notify_peers(ffff88104ffa4de0) [ 73.830592] [] team_port_enable.part.40+0x78/0x90 [team] [ 74.796738] team1: team_notify_peers(ffff88104f5df080) [ 75.165577] [] team_port_enable.part.40+0x78/0x90 [team] [ 75.694968] team1: team_notify_peers(ffff88104f5df080) [ 75.694984] [] team_port_disable+0x123/0x160 [team] [ 77.316488] team1: team_notify_peers(ffff88104f5df080) [ 77.663122] [] team_port_enable.part.40+0x78/0x90 [team] [ 78.470488] team1: team_notify_peers(ffff88104f5df080) [ 78.814722] [] team_port_disable+0x123/0x160 [team] [ 82.690765] team2: team_notify_peers(ffff88083d24df40) [ 83.083540] [] team_port_enable.part.40+0x78/0x90 [team] [ 83.942458] team2: team_notify_peers(ffff88083d24df40) [ 84.286446] [] team_port_disable+0x123/0x160 [team] [ 86.089955] team3: team_notify_peers(ffff88083fd14de0) [ 86.453495] [] team_port_enable.part.40+0x78/0x90 [team] [ 87.267773] team3: team_notify_peers(ffff88083fd14de0) [ 87.610203] [] team_port_disable+0x123/0x160 [team] which shows team_port_enable/disable getting invoked in short succession. When looking at one of the team's notify_peers.count_pending value, I saw that it was negative and slowly counting down from 0xffff...ffff! This lead me believe that there is a race condition present in the .count_pending pattern that both team_notify_peers and team_mcast_rejoin employ. Can you comment on the following patch/workaround? Thanks, -- Joe -->8-- -->8-- -->8-- >>From b11d7dcd051a2f141c1eec0a43c4a4ddf0361d10 Mon Sep 17 00:00:00 2001 From: Joe Lawrence Date: Thu, 2 Oct 2014 14:24:26 -0400 Subject: [PATCH] team: avoid race condition in scheduling delayed work When team_notify_peers and team_mcast_rejoin are called, they both reset their respective .count_pending atomic variable. Then when the actual worker function is executed, the variable is atomically decremented. This pattern introduces a potential race condition where the .count_pending rolls over and the worker function keeps rescheduling until .count_pending decrements to zero again: THREAD 1 THREAD 2 ======== ======== team_notify_peers(teamX) atomic_set count_pending = 1 schedule_delayed_work team_notify_peers(teamX) atomic_set count_pending = 1 team_notify_peers_work atomic_dec_and_test count_pending = 0 (return) schedule_delayed_work team_notify_peers_work atomic_dec_and_test count_pending = -1 schedule_delayed_work (repeat until count_pending = 0) Instead of assigning a new value to .count_pending, use atomic_add to tack-on the additional desired worker function invocations. Signed-off-by: Joe Lawrence --- drivers/net/team/team.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c index d46df38..2b87e3f 100644 --- a/drivers/net/team/team.c +++ b/drivers/net/team/team.c @@ -647,7 +647,7 @@ static void team_notify_peers(struct team *team) { if (!team->notify_peers.count || !netif_running(team->dev)) return; - atomic_set(&team->notify_peers.count_pending, team->notify_peers.count); + atomic_add(team->notify_peers.count, &team->notify_peers.count_pending); schedule_delayed_work(&team->notify_peers.dw, 0); } @@ -687,7 +687,7 @@ static void team_mcast_rejoin(struct team *team) { if (!team->mcast_rejoin.count || !netif_running(team->dev)) return; - atomic_set(&team->mcast_rejoin.count_pending, team->mcast_rejoin.count); + atomic_add(team->mcast_rejoin.count, &team->mcast_rejoin.count_pending); schedule_delayed_work(&team->mcast_rejoin.dw, 0); } -- 1.7.10.4