netdev - Re: [PATCH 1/2] rps: core implementation

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Date:	Thu, 19 Nov 2009 22:41:11 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] rps: core implementation

>> What are the standard deadlocks?  Looks like __send_remote_softirq
>> will call __smp_call_function with irq's disabled...
>
> The traditional deadlock (that was before the queue smp_call_function)
> was
>
> A                        B
>                         grab lock
> interrupts off
> spin on lock
>                         send IPI
>                         wait for specific CPU
>
> never answers because
> interrupts are off
>                         hangs forever
>
>
> I think with the queued smp_call_function it's better because
> the locks are only hold much shorter and that particular scenario
> is gone, but I'm not sure the problem has fully gone away.
>
> At least there are still plenty of WARN_ON( ... irqs_disabled()) in
> kernel/smp.c
>

So is send_remote_softirq also broken according to this?
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