FYI: various 11.0-CURRENT -r293227 (and older) hangs on arm (rpi2): a description of sorts

[Hans Petter Selasky]

On 01/07/16 22:26, Hans Petter Selasky wrote:
> On 01/07/16 21:20, Mark Millard wrote:
>>
>> On 2016-Jan-7, at 12:04 PM, Hans Petter Selasky <hps at selasky.org>
>> wrote:
>>>
>>> On 01/07/16 20:48, Ian Lepore wrote:
>>>> If the filesystems and swap space are on a usb drive, then maybe it's
>>>> the usb subsystem that's hanging.  The wait states you showed for those
>>>> processes are consistant with what I've seen when all buffers get
>>>> backed up in a queue on one non-responsive or slow device.  It may be
>>>> that there's a way to get the system deadlocked when it's low on
>>>> buffers and there is memory pressure causing the swap to be used (I
>>>> generally run arms systems without any swap configured).
>>>>
>>>> Running gstat in another window while this is going on may give you
>>>> some insight into the situation.  Beyond that I don't know what to look
>>>> at, especially since you generally can't launch any new tools once the
>>>> system gets into this kind of state.
>>>>
>>>> -- Ian
>>>
>>> Hi,
>>>
>>> All USB transfers towards disk devices have timeouts, so if something
>>> is hanging at USB level, you'll get a printout eventually.
>>
>> What sort of timescale after deadlock/live-lock is observed to
>> apparently have started does one have to wait in order to conclude
>> that the timeouts would have happened and so they do not apply to the
>> deadlock/live-lock?
>>
>>> The USB kernel processes needed for doing I/O transfers are not
>>> pinned to RAM. Can it happen if a USB process is swapped to disk,
>>> that the system cannot wakeup a swapped out process to get more swap?
>>>
>>> --HPS
>>
>
> Hi,
>
>> Wow. Could I use ddb to somehow check on the "USB kernel processes"
>> swap status when the overall context is deadlocked/live-locked?
>
> Are you able to run something like:
>
> ps auxwwH | grep usb
>
>  > If yes, how? Otherwise something in top or some such display that I'd
> left running over the serial console would have to present useful
> information on the subject. Is there anything that would?
>

Are you able to SSH into the box or ping it?

--HPS