linux-kernel - Re: [PATCH v7 2/4] nmi_backtrace: do a local dump

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Message-ID: <20160809123735.GF13300@pathway.suse.cz>
Date:	Tue, 9 Aug 2016 14:37:35 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Chris Metcalf <cmetcalf@...lanox.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/4] nmi_backtrace: do a local dump_stack() instead of
 a self-NMI

On Mon 2016-08-08 12:03:36, Chris Metcalf wrote:
> Currently on arm there is code that checks whether it should call
> dump_stack() explicitly, to avoid trying to raise an NMI when the
> current context is not preemptible by the backtrace IPI.  Similarly,
> the forthcoming arch/tile support uses an IPI mechanism that does
> not support generating an NMI to self.
> 
> Accordingly, move the code that guards this case into the generic
> mechanism, and invoke it unconditionally whenever we want a
> backtrace of the current cpu.  It seems plausible that in all cases,
> dump_stack() will generate better information than generating a
> stack from the NMI handler.  The register state will be missing,
> but that state is likely not particularly helpful in any case.
> 
> Or, if we think it is helpful, we should be capturing and emitting
> the current register state in all cases when regs == NULL is passed
> to nmi_cpu_backtrace().
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com>
> Acked-by: Aaron Tomlin <atomlin@...hat.com>

Sounds and looks fine to me.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr Mladek