linux-kernel - Re: [PATCH V2] smp: Give WARN()ing when calling smp_call_function

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Date:	Sun, 7 Jul 2013 11:59:07 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Chuansheng Liu <chuansheng.liu@...el.com>, mingo@...nel.org,
	peterz@...radead.org, jbeulich@...e.com,
	paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	mina86@...a86.org, srivatsa.bhat@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, jun.zhang@...el.com,
	fengguang.wu@...el.com
Subject: Re: [PATCH V2] smp: Give WARN()ing when calling
 smp_call_function_many()/single() in serving irq

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.
 

> And this is even more likely to happen than the lock issue.
> 
> Thanks,
> 
> 	tglx
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