linux-kernel - Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup

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Date:   Tue, 5 Jun 2018 16:43:45 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, mpe@...erman.id.au, mingo@...nel.org,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against
 wakeup

Hi Peter,

As last mentioned on mail, we are still seeing issue with the latest 
approach and below is the susceptible race as mentioned earlier..
controller Thread                               CPUHP Thread
takedown_cpu
kthread_park
kthread_parkme
Set KTHREAD_SHOULD_PARK
                                                 smpboot_thread_fn
                                                 set Task interruptible


wake_up_process
  if (!(p->state & state))
                 goto out;

                                                 Kthread_parkme
                                                 SET TASK_PARKED
                                                 schedule
                                                 raw_spin_lock(&rq->lock)
ttwu_remote
waiting for __task_rq_lock
                                                 context_switch

                                                 finish_lock_switch



                                                 Case TASK_PARKED
                                                 kthread_park_complete


SET Running


So it seems issue is still their with the latest mentioned fix
kthread, sched/wait: Fix kthread_parkme() completion issue.

Regards
Gaurav

On 5/7/2018 4:53 PM, Kohli, Gaurav wrote:
> Corrected the formatting, Sorry for spam.
> 
> 
>>
>> HI Peter,
>>
>> We have tested with new patch and still seeing same issue, in this 
>> dumps we don't have debug traces, but seems there still exist race 
>> from code review , Can you please check it once:
>>
>> Controller Thread                               CPUHP Thread
>> takedown_cpu
>> kthread_park
>> kthread_parkme
>> Set KTHREAD_SHOULD_PARK
>>                                                 smpboot_thread_fn
>>                                                 set Task interruptible
>>
>>
>> wake_up_process
>>
>>                                                 Kthread_parkme
>>                                                 SET TASK_PARKED
>>                                                 schedule
>>                                                 raw_spin_lock(&rq->lock)
>>
>>                                                 context_switch
>>
>>                                                 finish_lock_switch
>>
>>
>>
>>                                                 Case TASK_PARKED
>>                                                 kthread_park_complete
>>
>>
>> SET TASK_INTERRUPTIBLE
>>
>>
>> And also seeing the same warning during unpark of cpuhp from controller:
>>   if (!wait_task_inactive(p, state)) {
>>                  WARN_ON(1);
>>                  return;
>>          }
>> 325.065893] [<ffffff8920ed0200>] kthread_unpark+0x80/0xd8
>> [  325.065902] [<ffffff8920eab754>] bringup_cpu+0xa0/0x12c
>> [  325.065910] [<ffffff8920eaae90>] cpuhp_invoke_callback+0xb4/0x5c8
>> [  325.065917] [<ffffff8920eabd98>] cpuhp_up_callbacks+0x3c/0x154
>> [  325.065924] [<ffffff8920ead220>] _cpu_up+0x134/0x208
>> [  325.065931] [<ffffff8920ead45c>] do_cpu_up+0x168/0x1a0
>> [  325.065938] [<ffffff8920ead4b8>] cpu_up+0x24/0x30
>> [  325.065948] [<ffffff89215b1408>] cpu_subsys_online+0x20/0x2c
>> [  325.065956] [<ffffff89215aac64>] device_online+0x70/0xb4
>> [  325.065962] [<ffffff89215aad78>] online_store+0xd0/0xdc
>> [  325.065971] [<ffffff89215a7424>] dev_attr_store+0x40/0x54
>> [  325.065982] [<ffffff89210d8a98>] sysfs_kf_write+0x5c/0x74
>> [  325.065988] [<ffffff89210d7b9c>] kernfs_fop_write+0xcc/0x1ec
>> [  325.065999] [<ffffff8921049288>] vfs_write+0xb4/0x1d0
>> [  325.066006] [<ffffff892104a858>] SyS_write+0x60/0xc0
>> [  325.066014] [<ffffff8920e83770>] el0_svc_naked+0x24/0x28
>>
>>
>> And after this same crash occured:
>> [  325.521307] [<ffffff8920ed4aac>] smpboot_thread_fn+0x26c/0x2c8
>> [  325.527295] [<ffffff8920ecfb24>] kthread+0xf4/0x108
>>
>> I will put more debug ftraces to check what is going on exactly.
>>
>> Regards
>> Gaurav
>>
>>
>>
>>
> 

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