Re: [3.0-rc3] tree RCU boost vs hang notifier...

[Daniel J Blueman]

On 14 June 2011 12:51, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Jun 14, 2011 at 12:02:24PM +0800, Daniel J Blueman wrote:
>> With 3.0-rc3 configured with CONFIG_TREE_PREEMPT_RCU, CONFIG_RCU_BOOST
>> and CONFIG_DETECT_HUNG_TASK, we see frequent task hung reports [1],
>> possibly as the tree RCU boost kthreads sleep uninterruptably.
>>
>> It looks like tinyRCU sleeps interruptably, so won't trigger the hangcheck.
>>
>> Thanks,
>>   Daniel
>>
>> --- [1]
>>
>> INFO: task rcub0:9 blocked for more than 120 seconds.
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> rcub0           D ffffffff81c29c80  6768     9      2 0x00000000
>>  ffff880221713ea0 0000000000000046 ffff880221713db0 ffffffff8171b825
>>  ffff880221712000 0000000000004000 ffff8802214d0000 ffff88022170c060
>>  ffff88022ec00000 0000000000010ac0 0000000000000001 ffff88022ec10ac0
>> Call Trace:
>>  [<ffffffff8171b825>] ? _raw_spin_unlock_irqrestore+0x75/0x80
>>  [<ffffffff8171822a>] ? preempt_schedule+0x3a/0x50
>>  [<ffffffff8171b825>] ? _raw_spin_unlock_irqrestore+0x75/0x80
>>  [<ffffffff810cec90>] ? rcu_boost+0x120/0x120
>>  [<ffffffff8107e1a3>] kthread+0x93/0xc0
>>  [<ffffffff81098bad>] ? trace_hardirqs_on_caller+0x13d/0x180
>>  [<ffffffff8171d4d4>] kernel_thread_helper+0x4/0x10
>>  [<ffffffff81048ad7>] ? finish_task_switch+0x77/0x100
>>  [<ffffffff8171bc04>] ? retint_restore_args+0xe/0xe
>>  [<ffffffff8107e110>] ? __init_kthread_worker+0x70/0x70
>>  [<ffffffff8171d4d0>] ? gs_change+0xb/0xb
>> no locks held by rcub0/9.
>
> Hello, Daniel,
>
> Does the following patch help?
>
>                                                        Thanx, Paul
>
> ------------------------------------------------------------------------
>
> rcu: Simplify curing of load woes
>
> Make the functions creating the kthreads wake them up.  Leverage the
> fact that the per-node and boost kthreads can run anywhere, thus
> dispensing with the need to wake them up once the incoming CPU has
> gone fully online.
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
[]

Superb - this addresses the hangcheck warnings.

Tested-by: Daniel J Blueman <daniel.blueman@xxxxxxxxx>

Thanks,
  Daniel
-- 
Daniel J Blueman
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