linux-kernel - Re: WARNING: at kernel/smp.c:385 smp_call_function

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Message-ID: <51708FE5.6000301@oracle.com>
Date:	Thu, 18 Apr 2013 20:29:25 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>,
	"eag0628@...il.com" <eag0628@...il.com>,
	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: WARNING: at kernel/smp.c:385 smp_call_function_many

Hi Liu,

On 04/18/2013 08:10 PM, Liu, Chuansheng wrote:
>> It seems that with commit "smp: Give WARN()ing when calling
>> > smp_call_function_many()/single() in serving irq" I'm getting a bunch of these:
> This patch gives the warning even when the smp_call_function_many() is called in softirq context,
> because it will bring the possible deadlock cases, the example is below:
> CPUA                            CPUB
>                                 spin_lock(&spinlock)
>                                 Any irq coming, call the irq handler
>                                 irq_exit()
> spin_lock_irq(&spinlock)
> <== Blocking here due to
> CPUB hold it
>                                   __do_softirq()
>                                     run_timer_softirq()
>                                       timer_cb()
>                                         call smp_call_function_many()
>                                           send IPI interrupt to CPUA
>                                             wait_csd()
> 
> Then both CPUA and CPUB will be deadlocked here.

Right.

So commit f55a6faa3 ("hrtimer: Provide clock_was_set_delayed()") followed by one
of the commits that used clock_was_set_delayed() may trigger the deadlock you've
described. (cc John Stultz...)


Thanks,
Sasha
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