linux-kernel - Re: [RESEND PATCH 4.0-rc7 v20 2/6] irqchip: gic: Make gic_raise

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Message-ID: <55364887.2000404@arm.com>
Date:	Tue, 21 Apr 2015 13:54:31 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Daniel Thompson <daniel.thompson@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
CC:	Russell King <linux@....linux.org.uk>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	John Stultz <john.stultz@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Daniel Drake <drake@...lessm.com>,
	Dmitry Pervushin <dpervushin@...il.com>,
	Tim Sander <tim@...eglstein.org>
Subject: Re: [RESEND PATCH 4.0-rc7 v20 2/6] irqchip: gic: Make gic_raise_softirq
 FIQ-safe

On 10/04/15 10:51, Daniel Thompson wrote:
> It is currently possible for FIQ handlers to re-enter gic_raise_softirq()
> and lock up.
> 
>     	gic_raise_softirq()
> 	   lock(x);
> -~-> FIQ
>         handle_fiq()
> 	   gic_raise_softirq()
> 	      lock(x);		<-- Lockup
> 
> arch/arm/ uses IPIs to implement arch_irq_work_raise(), thus this issue
> renders it difficult for FIQ handlers to safely defer work to less
> restrictive calling contexts.
> 
> This patch fixes the problem by converting the cpu_map_migration_lock
> into a rwlock making it safe to re-enter the function.
> 
> Note that having made it safe to re-enter gic_raise_softirq() we no
> longer need to mask interrupts during gic_raise_softirq() because the
> b.L migration is always performed from task context.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jason Cooper <jason@...edaemon.net>
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>

Acked-by: Marc Zyngier <marc.zyngier@....com>

	M.
-- 
Jazz is not dead. It just smells funny...
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