Re: [PATCH] kdump: Fix crash_kexec - smp_send_stop race in panic

From: Richard Kuo <rkuo@codeaurora.org>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
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	Andrew Morton <akpm@linux-foundation.org>,
	Koichi Yasutake <yasutake.koichi@jp.panasonic.com>,
	Helge Deller <deller@gmx.de>
Subject: Re: [PATCH] kdump: Fix crash_kexec - smp_send_stop race in panic
Date: Fri, 11 Nov 2011 11:45:06 -0600	[thread overview]
Message-ID: <20111111174506.GE459@codeaurora.org> (raw)
In-Reply-To: <1321014494.2745.7.camel@br98xy6r>

On Fri, Nov 11, 2011 at 01:28:14PM +0100, Michael Holzheu wrote:
> Hello Chris,
> 
> On Thu, 2011-11-10 at 10:11 -0500, Chris Metcalf wrote:
> > On 11/10/2011 9:22 AM, Michael Holzheu wrote:
> 
> [snip]
> 
> > If a cleaner API seems useful (either for power reasons or restartability 
> > or whatever), I suppose a standard global function name could be specified 
> > that's the thing you execute when you get an smp_send_stop IPI (in tile's 
> > case it's "smp_stop_cpu_interrupt()") and the panic() code could instead 
> > just do an atomic_inc_return() of a global panic counter, and if it wasn't 
> > the first panicking cpu, call directly into the smp_stop handler routine to 
> > quiesce itself.  Then the panicking cpu could finish whatever it needs to 
> > do and then halt, reboot, etc., all the cpus.
> 
> Thanks for the info. So introducing a "weak" function that can stop the
> CPU it is running on could solve the problem. Every architecture can
> override the function with something appropriate. E.g. "tile" can use
> the lower-power "nap" instruction there.
> 
> What about the following patch.

Hexagon uses interrupts to send the stop to the other CPU's as well, and
we also have a stop local cpu operation defined, so I think we're in the same
boat as tile.  This patch should work for us.

-- 

Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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