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SubjectRe: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup
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Date
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
>>
>>
>>
>>
>

--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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