Re: [Xen-devel] [PATCH 1/2] common/kexec: Prevent deadlock on reentry to the crash path.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/11/13 13:28, Jan Beulich wrote:
>>>> On 15.11.13 at 21:32, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 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@xxxxxxxxxx>
>> CC: Keir Fraser <keir@xxxxxxx>
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Tim Deegan <tim@xxxxxxx>
>> CC: David Vrabel <david.vrabel@xxxxxxxxxx>
>> ---
>>  xen/common/kexec.c |   51 
>> ++++++++++++++++++++++++++++++++++++++++++++-------
>>  1 file changed, 44 insertions(+), 7 deletions(-)
> David, you being the maintainer of this code now, I don't think I've
> seen a response from you on this patch, despite - iirc - Andrew
> having pinged you on it already too.
>
> Jan
>

David is out of the office for a week on vacation at the moment.

I did get code-review from him before submitting it upstream, but I
guess that doesn't count for much as a formal ack.

~Andrew

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