linux-kernel - Re: [PATCH] ARM: Fix deadlock scenario with smp_send

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Date:	Wed, 24 Jul 2013 13:29:00 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: Fix deadlock scenario with smp_send_stop()

On 07/24/13 13:21, Russell King - ARM Linux wrote:
> On Wed, Jul 24, 2013 at 11:56:18AM -0700, Stephen Boyd wrote:
>> On 07/09, Stephen Boyd wrote:
>>> If one process calls sys_reboot and that process then stops other
>>> CPUs while those CPUs are within a spin_lock() region we can
>>> potentially encounter a deadlock scenario like below.
>>>
>>> CPU 0                   CPU 1
>>> -----                   -----
>>>                         spin_lock(my_lock)
>>> smp_send_stop()
>>>  <send IPI>             handle_IPI()
>>>                          disable_preemption/irqs
>>>                           while(1);
>>>  <PREEMPT>
>>> spin_lock(my_lock) <--- Waits forever
>>>
>>> We shouldn't attempt to run any other tasks after we send a stop
>>> IPI to a CPU so disable preemption so that this task runs to
>>> completion.
>>>
>>> Reported-by: Sundarajan Srinivasan <sundaraj@...eaurora.com>
>>> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>>> ---
>>>
>>> Resending this patch now that the context has changed.
>> Ping? Shall I put this in the patch tracker?
> Well, looking at x86, they use local_irq_disable() before sending the
> stop, so I think we should do the same for cross-arch consistency.

Fair enough. I'll send v2 with that.

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