linux-kernel - Re: [PATCH v2] kdump: Fix crash_kexec

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Date:	Wed, 02 Nov 2011 11:03:59 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, heiko.carstens@...ibm.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	schwidefsky@...ibm.com, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v2] kdump: Fix crash_kexec - smp_send_stop race in panic

On Tue, 2011-11-01 at 16:04 -0400, Don Zickus wrote:
> On Mon, Oct 31, 2011 at 01:34:19PM +0100, Michael Holzheu wrote:
> > Hello Andrew, hello linux-arch,
> > 
> > > Well OK.  Maybe some architectures do have this problem - who would
> > > notice?  If that is the case, we just made the failure cases much more
> > > common.  Could you check, please?
> > 
> > @linux-arch: 
> > 
> > This patch introduces a spinlock to prevent parallel execution of the
> > panic code. Andrew pointed out that this might be a problem for
> > architectures that can't do smp_send_stop() on remote CPUs that have
> > interrupts disabled. When irq-disabled CPUs execute panic() in parallel,
> > we then would have looping CPUs.
> 
> x86 has such problem and I posted a patch recently to fix it
> 
> https://lkml.org/lkml/2011/10/13/426

Ok good, so with this patch x86 has no problem with the panic spinlock.
Anybody else?

Instead of introducing the panic lock, as an alternative we could move
smp_send_stop() to the beginning of panic(). Eric told me that the
function is currently "insufficiently reliable" for that, but perhaps we
could make it more reliable.

Michael



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