[PATCH] xen/mce: add .poll method for mcelog device driver

[Liu, Jinsong]

 >> 
>> So another bug which is that mcelog is spinning at 100% CPU (and
>> only under Xen). 
>> 
>> It seems to be doing:
>> 
>> ppoll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}], 2, NULL, [], 8)
>> = 1 ([{fd=3, revents=POLLIN}]) read(3, "", 2816)
>> = 0
>> ppoll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}], 2, NULL, [], 8)
>> = 1 ([{fd=3, revents=POLLIN}]) read(3, "", 2816)
>> 
>> constantly.
> 
> I will debug it. I have try at my platform, but fail to reproduce it.
> (You still use the config you send me last time, right?) Would you
> tell me your step? 
> 
> Thanks,
> Jinsong

Have a look at it, it caused by NULL .poll method.
Attached is the patch to fix this bug, but I cannot reproduce the bug at my platform, so would you please help me to test it at your side?

Thanks,
Jinsong

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