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Date: Fri, 3 Oct 2014 10:04:43 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Joe Lawrence <joe.lawrence@...atus.com>
Cc: netdev@...r.kernel.org
Subject: Re: bug: race in team_{notify_peers,mcast_rejoin} scheduling
Thu, Oct 02, 2014 at 08:50:28PM CEST, joe.lawrence@...atus.com wrote:
>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] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 69.622395] team0: team_notify_peers(ffff88104ffa4de0)
>[ 69.966758] [<ffffffffa034ef63>] team_port_disable+0x123/0x160 [team]
>[ 71.099263] team0: team_notify_peers(ffff88104ffa4de0)
>[ 71.466243] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 72.383788] team0: team_notify_peers(ffff88104ffa4de0)
>[ 72.744778] [<ffffffffa034ef63>] team_port_disable+0x123/0x160 [team]
>[ 73.476190] team0: team_notify_peers(ffff88104ffa4de0)
>[ 73.830592] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 74.796738] team1: team_notify_peers(ffff88104f5df080)
>[ 75.165577] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 75.694968] team1: team_notify_peers(ffff88104f5df080)
>[ 75.694984] [<ffffffffa034ef63>] team_port_disable+0x123/0x160 [team]
>[ 77.316488] team1: team_notify_peers(ffff88104f5df080)
>[ 77.663122] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 78.470488] team1: team_notify_peers(ffff88104f5df080)
>[ 78.814722] [<ffffffffa034ef63>] team_port_disable+0x123/0x160 [team]
>[ 82.690765] team2: team_notify_peers(ffff88083d24df40)
>[ 83.083540] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 83.942458] team2: team_notify_peers(ffff88083d24df40)
>[ 84.286446] [<ffffffffa034ef63>] team_port_disable+0x123/0x160 [team]
>[ 86.089955] team3: team_notify_peers(ffff88083fd14de0)
>[ 86.453495] [<ffffffffa034fd38>] team_port_enable.part.40+0x78/0x90 [team]
>[ 87.267773] team3: team_notify_peers(ffff88083fd14de0)
>[ 87.610203] [<ffffffffa034ef63>] 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?
Well, I can't see a better solution. Adding is fine here I believe.
Acked-by: Jiri Pirko <jiri@...nulli.us>
Please send to patch with my ack and with:
Fixes: fc423ff00df3a19554414ee ("team: add peer notification")
So it can be pushed to stable.
Thanks!
>
>Thanks,
>
>-- Joe
>
>-->8-- -->8-- -->8--
>
>>From b11d7dcd051a2f141c1eec0a43c4a4ddf0361d10 Mon Sep 17 00:00:00 2001
>From: Joe Lawrence <joe.lawrence@...atus.com>
>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 <joe.lawrence@...atus.com>
>---
> 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
>
>
>
--
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