On 2013/3/3 3:23, Tommi Rantala wrote:
> Hello,
>
> I'm seeing the following hung task warnings when fuzzing the kernel
> with trinity (in a qemu virtual machine, as the root user), that I
> have not seen before with 3.8 or earlier. The kernel is
> b0af9cd9aab60ceb17d3ebabb9fdf4ff0a99cf50 (Merge tag
> 'lzo-update-signature-20130226' of
> git://github.com/markus-oberhumer/linux).
>
This doesn't look like a cgroup bug.
...
> [ 120.594088] INFO: task kworker/0:2:1079 blocked for more than 60 seconds.
> [ 120.595877] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 120.598100] kworker/0:2 D ffff88007c518618 0 1079 2 0x00000000
> [ 120.599958] ffff88007adc9a38 0000000000000046 ffff88007b0b0000
> ffff88007adc9fd8
> [ 120.601982] ffff88007adc9fd8 ffff88007adc9fd8 ffff88007c518000
> ffff88007b0b0000
> [ 120.603994] ffff88007adc9a18 ffff88007adc9b88 ffff88007adc9b90
> 7fffffffffffffff
> [ 120.606003] Call Trace:
> [ 120.606684] [<ffffffff81cd9d95>] schedule+0x55/0x60
> [ 120.607973] [<ffffffff81cd7786>] schedule_timeout+0x36/0x240
> [ 120.609460] [<ffffffff810f3303>] ? mark_held_locks+0x123/0x140
> [ 120.610932] [<ffffffff81cdb99b>] ? _raw_spin_unlock_irq+0x2b/0x40
> [ 120.612521] [<ffffffff810f3475>] ? trace_hardirqs_on_caller+0x155/0x1f0
> [ 120.614471] [<ffffffff810f351d>] ? trace_hardirqs_on+0xd/0x10
> [ 120.615957] [<ffffffff81cda037>] wait_for_completion+0x97/0x100
> [ 120.617495] [<ffffffff810d2310>] ? try_to_wake_up+0x340/0x340
> [ 120.619013] [<ffffffff810b615c>] call_usermodehelper_exec+0x14c/0x210
> [ 120.620613] [<ffffffff81cd9fcc>] ? wait_for_completion+0x2c/0x100
> [ 120.622187] [<ffffffff810b6948>] call_usermodehelper_fns+0xe8/0x100
> [ 120.623821] [<ffffffff8110921a>] cgroup_release_agent+0x15a/0x180
> [ 120.625374] [<ffffffff810b85cb>] process_one_work+0x29b/0x4c0
> [ 120.626861] [<ffffffff810b8560>] ? process_one_work+0x230/0x4c0
> [ 120.628407] [<ffffffff810b8da8>] worker_thread+0x248/0x380
> [ 120.630183] [<ffffffff810b8b60>] ? busy_worker_rebind_fn+0xb0/0xb0
> [ 120.631761] [<ffffffff810bfd71>] kthread+0xd1/0xe0
> [ 120.633019] [<ffffffff810f351d>] ? trace_hardirqs_on+0xd/0x10
> [ 120.634479] [<ffffffff810bfca0>] ? __kthread_bind+0x40/0x40
> [ 120.635898] [<ffffffff81cdcdfc>] ret_from_fork+0x7c/0xb0
> [ 120.637254] [<ffffffff810bfca0>] ? __kthread_bind+0x40/0x40
The completion was never done:
static
int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
{
DECLARE_COMPLETION_ONSTACK(done);
...
sub_info->complete = &done;
sub_info->wait = wait;
queue_work(khelper_wq, &sub_info->work);
...
wait_for_completion(&done);
...
return retval;
}
It should be done here:
static void __call_usermodehelper(struct work_struct *work)
{
...
pid = kernel_thread(call_helper, sub_info,
CLONE_VFORK | SIGCHLD);
...
switch (wait) {
...
case UMH_WAIT_EXEC:
if (pid < 0)
sub_info->retval = pid;
umh_complete(sub_info);
}
}
You may need to add some printks to see why completion can't be done.
Maybe khelper_wq was blocked and couldn't schedule any work?
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