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

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Message-ID: <20130707024113.GA2767@udknight>
Date:	Sun, 7 Jul 2013 10:41:13 +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 03:50:57PM +0200, Thomas Gleixner wrote:
> On Sat, 16 Feb 2013, Chuansheng Liu wrote:
> > There is a real case for softirq DEADLOCK case:
> > 
> > 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.
> 

Why can't we just use spin_lock_irq instead of spin_lock in CPUB to
prevent this to happen ?

And the according senario for kernel/smp.c is to use raw_spin_lock_irqsave
instead of raw_spin_lock in generic_smp_call_function_single_interrupt
to protect the follow one line codes:

        raw_spin_lock(&q->lock);
        list_replace_init(&q->list, &list);
        raw_spin_unlock(&q->lock);

Thanks.
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