netdev - Re: reproducable panic eviction work queue

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Date:	Wed, 22 Jul 2015 15:58:55 +0200
From:	Florian Westphal <fw@...len.de>
To:	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:	Frank Schreuder <fschreuder@...nsip.nl>,
	Florian Westphal <fw@...len.de>,
	Johan Schuijt <johan@...nsip.nl>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"nikolay@...hat.com" <nikolay@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"chutzpah@...too.org" <chutzpah@...too.org>,
	Robin Geuze <robing@...nsip.nl>,
	netdev <netdev@...r.kernel.org>
Subject: Re: reproducable panic eviction work queue

Nikolay Aleksandrov <nikolay@...ulusnetworks.com> wrote:
> On 07/22/2015 10:17 AM, Frank Schreuder wrote:
> > I got some additional information from syslog:
> > 
> > Jul 22 09:49:33 dommy0 kernel: [  675.987890] NMI watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kworker/3:1:42]
> > Jul 22 09:49:42 dommy0 kernel: [  685.114033] INFO: rcu_sched self-detected stall on CPU { 3}  (t=39918 jiffies g=988 c=987 q=23168)
> > 
> > Thanks,
> > Frank
> > 
> > 
> 
> Hi,
> It looks like it's happening because of the evict_again logic, I think we should also
> add Florian's first suggestion about simplifying it to the patch and just skip the
> entry if we can't delete its timer otherwise we can restart the eviction and see
> entries that already had their timer stopped by us and can keep restarting for
> a long time.
> Here's an updated patch that removes the evict_again logic.

Thanks Nik.  I'm afraid this adds bug when netns is exiting.

Currently, we wait until timer has finished, but after the change
we might destroy percpu counter while a timer is still executing on
another cpu.

I pushed a patch series to
https://git.breakpoint.cc/cgit/fw/net.git/log/?h=inetfrag_fixes_02

It includes this patch with a small change -- deferral of the percpu
counter subtraction until after queue has been free'd.

Frank -- it would be great if you could test with the four patches in
that series applied.

I'll then add your tested-by Tag to all of them before submitting this.

Thanks again for all your help in getting this fixed!
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