From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <dvrabel@cantab.net>
Subject: Re: [PATCH 1/2] common/kexec: Prevent deadlock on
 reentry to the crash path.
Date: Wed, 27 Nov 2013 10:27:11 +0000
Message-ID: <5295C8FF.3060204@cantab.net>
References: <1384547567-17059-1-git-send-email-andrew.cooper3@citrix.com>
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To: Andrew Cooper <andrew.cooper3@citrix.com>, Xen-devel <xen-devel@lists.xen.org>
Cc: Tim Deegan <tim@xen.org>, Keir Fraser <keir@xen.org>, David Vrabel <david.vrabel@citrix.com>, Jan Beulich <JBeulich@suse.com>
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On 15/11/2013 20:32, Andrew Cooper wrote:
> In some cases, such as suffering a queued-invalidation timeout while
> performing an iommu_crash_shutdown(), Xen can end up reentering the crash
> path. Previously, this would result in a deadlock in one_cpu_only(), as the
> test_and_set_bit() would fail.
> 
> The crash path is not reentrant, and even if it could be made to be so, it is
> almost certain that we would fall over the same reentry condition again.
> 
> The new code can distinguish a reentry case from multiple cpus racing down the
> crash path.  In the case that a reentry is detected, return back out to the
> nested panic() call, which will maybe_reboot() on our behalf.  This requires a
> bit of return plumbing back up to kexec_crash().
> 
> While fixing this deadlock, also fix up an minor niggle seen recently from a
> XenServer crash report.  The report was from a Bank 8 MCE, which had managed
> to crash on all cpus at once.  The result was a lot of stack traces with cpus
> in kexec_common_shutdown(), which was infact the inlined version of
> one_cpu_only().  The kexec crash path is not a hotpath, so we can easily
> afford to prevent inlining for the sake of clarity in the stack traces.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Keir Fraser <keir@xen.org>
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Tim Deegan <tim@xen.org>
> CC: David Vrabel <david.vrabel@citrix.com>

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

David