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SubjectRe: [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

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.


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