On Fri, Jun 26, 2020 at 7:35 PM sven falempin <sven.falem...@gmail.com>
wrote:

>
>
> On Fri, Jun 26, 2020 at 5:22 PM Stuart Henderson <s...@spacehopper.org>
> wrote:
>
>> On 2020/06/26 15:30, sven falempin wrote:
>> > behavior confirmed on current.
>> >
>> > Once the process stalls,  ( could be anything writing to the vnconfig
>> disk,
>> > cp , umount )
>> > a few other calls like df , or ps, etc may hang, never the same
>> > sp or mp kernel, reproduced on today's snapshots.
>>
>> vnconfig is used as part of "make release", many builds are done every
>> week using this so it's not a general problem with vnconfig.
>>
>> Can you show some commands or a script to trigger the behaviour?
>>
>
> the perl script use the system to call :
>
> vnconfig.
> mount.
> umount. <- saw hanged
> cp.<- saw hanged
> tar.<- saw hanged
> svn up.<- saw hanged
> and dd.
> newfs.
>
> really nothing fancy, only stuff writing to disk got stuck.
>
> At one point it does a chroot but it never hangs near that , most of the
> time it hangs before.
>
> The script has been used like 1000 times on 6.0 and maybe twice more on
> 6.4.
>
> I have absolutely no idea what the 'needbuf' of top is .
>
> the script hangs at random position , always writing into vnconfig.
>
> I have no idea how to reproduce outside the perl script , so maybe it is
> related
> to some devious perl stdin/stdout buffer .
>
> Nevertheless there's like a 5% chance that's the script will work( slowly )
>
> Most of the system call are inside a routine to log
>
> sub debug_system {
>   $logger->debug('running: '.join(' ', @_));
>   return system(@_);
> }
>
> so i can easily put things inside to try to understand the issue.
>
> It is really a strange behavior, and the device must be shut down
> electrically.
> Something really odd, i run syslogd on a buffer, and syslogc buffer is
> stuck too
> when the device stuck (but it supposed to be mostly already allocated
> memory ).
>
> It's really like the vm does not want to give anymore bucket (<- i
> don't know what i m talking about here,
> but i looks like that anything that doesn't malloc is ok , computer reply
> to ping , can do a few things for a while , and then complete
> hang )
>
> I ran the 6.7 release on a VM somewhere and another device with many perl
> script and they work.
>
> Only this fails 95% of the time and is VERY VERY slow when ok.
> compared to what i saw in /usr/src the vnconfig is big ,  ( forgot to copy
> df -h  ),
> like 2GB
>


i put ktrace in front of the perl system call

An di was able to recover a 800MB trace

$ kdump -f ./trace.out | tail -20
kdump: realloc: Cannot allocate memory
 25955         UNKNOWN(1634890859)
 72466 ▒▒▒     CALL  syscall()


could that be of some use ?


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