Re: [PATCH V2] smp: Give WARN()ing when callingsmp_call_function_many()/single() in serving irq
From: Wang YanQing
Date: Sat Jul 06 2013 - 22:42:03 EST
On Fri, Jul 05, 2013 at 03:50:57PM +0200, Thomas Gleixner wrote:
>
On 2013年2月16日, 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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