Re: [uml-devel] [PATCH v3] um: Switch clocksource to hrtimers

[Richard Weinberger <richard@nod.at>]

Am 31.10.2015 um 16:44 schrieb Thomas Meyer:
> Am Samstag, den 31.10.2015, 16:30 +0100 schrieb Richard Weinberger:
>> Am 31.10.2015 um 16:24 schrieb Thomas Meyer:
>>> Am Samstag, den 31.10.2015, 16:21 +0100 schrieb Richard Weinberger:
>>>> Am 31.10.2015 um 16:16 schrieb Thomas Meyer:
>>>>> mhh. strange. I didn't see this behaviour on my machine, but my
>>>>> machine
>>>>> is a rare single core system so, likely a race condition while
>>>>> relaying
>>>>> the timer interrupt to the userspace process.
>>>>
>>>> Here I can trigger it by starting UML, logging in and waiting
>>>> ~5min.
>>>> Then i try to run "top" --> top hangs forever.
>>>>
>>>>> But I'm out of ideas how this could happen!
>>>>
>>>> Maybe some stupid timeslice over/underflow.
>>>>
>>>>> what happens when you send the hanging process a SIGVTALRM
>>>>> signal?
>>>>> does
>>>>> it proceed correctly?
>>>>
>>>> You mean sending SIGVTALRM to the UML host process?
>>>
>>> No, to the hanging userspace process, maybe the uml host process
>>> did
>>> receive a timer interrupt, but failed to relay this signal to the
>>> correct userspace process.
>>
>> Well, this is not what top expects and dies.
>>         signal 26 (VTALRM) was caught by top, please
>>         see http://www.debian.org/Bugs/Reporting
>>

This happens when i send the signal _within_ UML.
Of course, top terminates.

> So you did send a VTALARM in the UML system to the top process?
> When yes then this was a misunderstanding! I wanted you to send a
> SIGVTALRM on the uml host system to the hanging pid. does this resolve
> the hang?

I also sent SIGVTALRM to the hanging pid on the host side.
It did not help. :(

Thanks,
//richard

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