Re: [Xen-devel] xenstored crashes with SIGSEGV

[Philipp Hahn <hahn@xxxxxxxxxxxxx>]

Hello,

happy new year to everyone.

On 19.12.2014 13:36, Philipp Hahn wrote:
> On 18.12.2014 11:17, Ian Campbell wrote:
>> On Tue, 2014-12-16 at 16:13 +0000, Frediano Ziglio wrote:
>>> Do we have a bug in Xen that affect SSE instructions (possibly already
>>> fixed after Philipp version) ?
>>
>> I've had a niggling feeling of Deja Vu over this which I'd been putting
>> down to an old Xen on ARM bug in the area of FPU register switching.
>>
>> But it seems at some point (possibly even still) there was a similar
>> issue with pvops kernels on x86, see:
>>         http://bugs.xenproject.org/xen/bug/40
> 
> That definitely looks interesting.
> 
>> Philipp, what kernel are you guys using?
> 
> The crash "2014-12-06 01:26:21 xenstored[4337]" happened on linux-3.10.46.

I looked through the changes of v3.10.46..v3.10.63 and found the
following patches:
| fb5b6e7 x86, fpu: shift drop_init_fpu() from save_xstate_sig() to
handle_signal()
| b888e3d x86, fpu: __restore_xstate_sig()->math_state_restore() needs
preempt_disable()

They look interesting enough to may have fixed the bug, which could
explain the strange bit pattern caused by not restoring the FPU state
correctly. Because of that and because of the missing

>> commit d1cc001905146d58c17ac8452eb96f226767819d
>> Author: Silesh C V <svellattu@xxxxxxxxxx>
>> Date:   Wed Jul 23 13:59:59 2014 -0700
>>
>>     coredump: fix the setting of PF_DUMPCORE
>>     commit aed8adb7688d5744cb484226820163af31d2499a upstream.

we're now working on upgrading the dom0 kernel which should give use
usable core dumps again and may also fix the underlying problem. It that
bug ever happens again I'll keep you informed.

Thanks so far to everybody for the excellent support.

Sincerely
Philipp Hahn

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