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Date: Sat, 5 Jul 2014 19:10:15 +0100
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: pawandeep oza <oza.contri.linux.kernel@gmail.com>
Cc: akpm@linux-foundation.org, holt@sgi.com, mingo@kernel.org,
        sboyd@codeaurora.org, k.khlebnikov@samsung.com,
        u.kleine-koenig@pengutronix.de, nicolas.pitre@linaro.org,
        linux-arm-kernel@lists.infradead.or, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] machine_power_off: not only local_irq_disable but also
	do disable preemption
Message-ID: <20140705181015.GQ21766@n2100.arm.linux.org.uk>
References: <CAA-nRyoO_NmrD8aRa3OyVXz4b133Fxi0=biGXTzSPDuSuNJJxQ@mail.gmail.com>
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On Sat, Jul 05, 2014 at 10:44:41PM +0530, pawandeep oza wrote:
>  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

Please explain how that <PREEMPT> occurs with IRQs already disabled.

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