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

[Richard Weinberger <richard@nod.at>]

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

The problem is within UML's scheduler it does not wake top
after the nanosleep() expires.
Maybe the new clock is too imprecise, dunno.

Thanks,
//richard

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