linux-kernel - Re: [PATCH] machine_power_off: not only local_irq

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Message-ID: <20140705181015.GQ21766@n2100.arm.linux.org.uk>
Date:	Sat, 5 Jul 2014 19:10:15 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	pawandeep oza <oza.contri.linux.kernel@...il.com>
Cc:	akpm@...ux-foundation.org, holt@....com, mingo@...nel.org,
	sboyd@...eaurora.org, k.khlebnikov@...sung.com,
	u.kleine-koenig@...gutronix.de, nicolas.pitre@...aro.org,
	linux-arm-kernel@...ts.infradead.or, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] machine_power_off: not only local_irq_disable but also
	do disable preemption

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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