linux-kernel - Re: [PATCH v2] metag: kick: add missing irq_enter/exit to kick

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Date:	Tue, 2 Jul 2013 14:28:51 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	James Hogan <james.hogan@...tec.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] metag: kick: add missing irq_enter/exit to
 kick_handler()

On Tue, 2 Jul 2013, James Hogan wrote:

> kick_handler() doesn't have an irq_enter/exit pair, but it's used for
> handling SMP IPIs which require work to be done in softirqs, which are
> invoked from irq_exit() when the hard irq nest count reaches 0.
> 
> The scheduler_ipi() callback in the IPI handler calls irq_enter/exit
> itself, but this is inside kick_handler()'s spin lock critical section,
> so if an invoked softirq issues an IPI the kick_handler() will be
> re-entered on the same CPU and will deadlock.
> 
> This is easily fixed by adding the missing irq_enter/exit to
> kick_handler() so that the hard irq nest count doesn't reach 0 until
> after the spin lock has been released.
> 
> Ideally the spin lock protected handler list will also be replaced by a
> lockless RCU protected list since it is certainly mostly read. That can
> be done in a later change though.
> 
> Signed-off-by: James Hogan <james.hogan@...tec.com>

Acked-by: Thomas Gleixner <tglx@...utronix.de>
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