linux-kernel - Re: CPU softlockup due to smp_call

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Message-ID: <4F7D8F16.9090904@redhat.com>
Date:	Thu, 05 Apr 2012 15:24:54 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Dave Jones <davej@...hat.com>, kvm@...r.kernel.org,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: CPU softlockup due to smp_call_function()

On 04/04/2012 11:12 PM, Sasha Levin wrote:
> Hi all,
>
> I've starting seeing soft lockups resulting from smp_call_function()
> calls. I've attached two different backtraces of this happening with
> different code paths.
>
> This is running inside a KVM guest with the trinity fuzzer, using
> today's linux-next kernel.
>
> [ 6540.134009] BUG: soft lockup - CPU#0 stuck for 22s! [kworker/u:1:38]
> [ 6540.134048] irq event stamp: 286811770
> [ 6540.134048] hardirqs last  enabled at (286811769):
> [<ffffffff82669e74>] restore_args+0x0/0x30
> [ 6540.134048] hardirqs last disabled at (286811770):
> [<ffffffff8266b3ea>] apic_timer_interrupt+0x6a/0x80
> [ 6540.134048] softirqs last  enabled at (286811768):
> [<ffffffff810b746e>] __do_softirq+0x16e/0x190
> [ 6540.134048] softirqs last disabled at (286811749):
> [<ffffffff8266bdec>] call_softirq+0x1c/0x30
> [ 6540.134048] CPU 0
> [ 6540.134048] Pid: 38, comm: kworker/u:1 Tainted: G        W
> 3.4.0-rc1-next-20120404-sasha-dirty #72
> [ 6540.134048] RIP: 0010:[<ffffffff8111f30e>]  [<ffffffff8111f30e>]
> smp_call_function_many+0x27e/0x2a0
>

This cpu is waiting for some other cpu to process a function (likely
rps_trigger_softirq(), from the trace).  Can you get a backtrace on all
cpus when this happens?

It would be good to enhance smp_call_function_*() to do this
automatically when it happens - it's spinning there anyway, so it might
as well count the iterations and NMI the lagging cpu if it waits for too
long.

-- 
error compiling committee.c: too many arguments to function

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