linux-kernel - Re: [PATCH 4/5] metag: kick: prevent nested kick handlers

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Date:	Mon, 1 Jul 2013 23:51:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	James Hogan <james.hogan@...tec.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] metag: kick: prevent nested kick handlers

On Mon, 1 Jul 2013, James Hogan wrote:

> The main kick trigger handler iterates a list of kick handlers and calls
> each one. This is done with the kick_handlers_lock spin lock held, but
> this causes a problem on SMP where IPIs are implemented with kicks. A
> reschedule IPI calls scheduler_ipi() which uses irq_enter() and
> irq_exit(). This results in the scheduler being invoked with
> kick_handlers_lock held which can result in a nested kick trigger
> attempting to acquire the lock, resulting in deadlock.
> 
> irq_enter() and irq_exit() can nest, so call them from the main kick
> interrupt handler so that softirqs are only handled after
> kick_handlers_lock is released.

This changelog is confusing. What I decode from the patch is, that you
are adding a missing irq_enter/exit pair to the kick_handler, right ?

Thanks,

	tglx
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