Re: oops in __delayacct_blkio_ticks with 2.6.18-rc4

[Shailabh Nagar <nagar@watson.ibm.com>]

Olaf Hering wrote:
> On Tue, Aug 22, Shailabh Nagar wrote:
> 
> 
>>Olaf Hering wrote:
>>
>>>https://bugzilla.novell.com/show_bug.cgi?id=200526
>>>
>>
>>Thanks for detecting this.
>>
>>I suspect the oops is caused by a reading of /proc/<tgid>/stat for some task
>>that is late in exit. Currently tsk->delays is being freed up too early (before
>>the tsk is removed from the tasklist).
>>
>>Could you try the patch below ? It was unclear from the bug what userspace
>>actions were being done to reproduce the oops - I suspect some kind of
>>reading of /proc/.../stat for all processes ?
> 
> 
> I dont have a way to trigger it. The commands were 'w' and 'pstree'.

Ok. Using the following two commands allowed the original oops to be
triggered on an 8-way pretty quickly:

while : ; do usleep 10 > /dev/null ; done

while : ; do cat /proc/[0-9]???*/stat ; done

(where the regex for catching the newly forking/exiting tasks
can be adjusted to the right range of ids being spawned by the
first command)

Applying the patch I sent solves the problem. I'm doing some more
testing and will submit the patch formally shortly.

Thanks,
Shailabh