linux-kernel - Re: [PATCH v3] arm: Fix backtrace generation when IPI is masked

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Message-ID: <alpine.DEB.2.11.1509221258330.5606@nanos>
Date:	Tue, 22 Sep 2015 12:59:00 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Thompson <daniel.thompson@...aro.org>
cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	Hillf Danton <hillf.zj@...baba-inc.com>
Subject: Re: [PATCH v3] arm: Fix backtrace generation when IPI is masked

On Tue, 15 Sep 2015, Daniel Thompson wrote:

> Currently on ARM when <SysRq-L> is triggered from an interrupt handler
> (e.g. a SysRq issued using UART or kbd) the main CPU will wedge for ten
> seconds with interrupts masked before issuing a backtrace for every CPU
> except itself.
> 
> The new backtrace code introduced by commit 96f0e00378d4 ("ARM: add
> basic support for on-demand backtrace of other CPUs") does not work
> correctly when run from an interrupt handler because IPI_CPU_BACKTRACE
> is used to generate the backtrace on all CPUs but cannot preempt the
> current calling context.
> 
> This can be fixed by detecting that the calling context cannot be
> preempted and issuing the backtrace directly in this case. Issuing
> directly leaves us without any pt_regs to pass to nmi_cpu_backtrace()
> so we also modify the generic code to call dump_stack() when its
> argument is NULL.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>

For the genric part.

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