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Date: Sun, 7 Jul 2013 15:47:12 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Wang YanQing <udknight@gmail.com>
cc: Chuansheng Liu <chuansheng.liu@intel.com>, mingo@kernel.org,
        peterz@infradead.org, jbeulich@suse.com, paulmck@linux.vnet.ibm.com,
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        srivatsa.bhat@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        jun.zhang@intel.com, fengguang.wu@intel.com
Subject: Re: [PATCH V2] smp: Give WARN()ing when calling smp_call_function_many()/single()
 in serving irq
In-Reply-To: <20130707035907.GA2875@udknight>
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On Sun, 7 Jul 2013, Wang YanQing wrote:
> On Fri, Jul 05, 2013 at 04:37:14PM +0200, Thomas Gleixner wrote:
> > Hmm, even there it matters, because of the following scenario:
> > 
> > CPU 0
> > smp_call_function_single(CPU 1)
> >     csd_lock(CPU 1)
> 
> No, smpl_call_function_single(CPU 1)
> will csd_lock(CPU 0), not csd_lock(CPU 1)
> 
> >     irq_enter()
> >     irq_exit()
> >     __do_softirq()
> >     smp_call_function_many()
> >       setup csd (CPU 1)
> >         csd_lock(CPU 1) ==> CPU 0 deadlocked itself.
> > 
> 
> maybe below is the scenario:
>      irq_enter()
>      irq_exit()
>      __do_softirq()
>      smp_call_function_single()
>        setup csd (CPU 1)
>          csd_lock(CPU 0) ==> CPU 0 deadlocked itself.

Right, I fatfingered that :)