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

[Kohli, Gaurav]

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 ThreadÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ CPUHP Thread
> > takedown_cpu
> > kthread_park
> > kthread_parkme
> > Set KTHREAD_SHOULD_PARK
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ smpboot_thread_fn
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ set Task interruptible
> >
> >
> > wake_up_process
> >
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Kthread_parkme
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ SET TASK_PARKED
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ schedule
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ raw_spin_lock(&rq->lock)
> >
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ context_switch
> >
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ finish_lock_switch
> >
> >
> >
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Case TASK_PARKED
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ kthread_park_complete
> >
> >
> > SET TASK_INTERRUPTIBLE
> >
> >
> > And also seeing the same warning during unpark of cpuhp from controller:
> > ÂÂif (!wait_task_inactive(p, state)) {
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ WARN_ON(1);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ return;
> > ÂÂÂÂÂÂÂÂ }
> > 325.065893] [<ffffff8920ed0200>] kthread_unpark+0x80/0xd8
> > [Â 325.065902] [<ffffff8920eab754>] bringup_cpu+0xa0/0x12c
> > [Â 325.065910] [<ffffff8920eaae90>] cpuhp_invoke_callback+0xb4/0x5c8
> > [Â 325.065917] [<ffffff8920eabd98>] cpuhp_up_callbacks+0x3c/0x154
> > [Â 325.065924] [<ffffff8920ead220>] _cpu_up+0x134/0x208
> > [Â 325.065931] [<ffffff8920ead45c>] do_cpu_up+0x168/0x1a0
> > [Â 325.065938] [<ffffff8920ead4b8>] cpu_up+0x24/0x30
> > [Â 325.065948] [<ffffff89215b1408>] cpu_subsys_online+0x20/0x2c
> > [Â 325.065956] [<ffffff89215aac64>] device_online+0x70/0xb4
> > [Â 325.065962] [<ffffff89215aad78>] online_store+0xd0/0xdc
> > [Â 325.065971] [<ffffff89215a7424>] dev_attr_store+0x40/0x54
> > [Â 325.065982] [<ffffff89210d8a98>] sysfs_kf_write+0x5c/0x74
> > [Â 325.065988] [<ffffff89210d7b9c>] kernfs_fop_write+0xcc/0x1ec
> > [Â 325.065999] [<ffffff8921049288>] vfs_write+0xb4/0x1d0
> > [Â 325.066006] [<ffffff892104a858>] SyS_write+0x60/0xc0
> > [Â 325.066014] [<ffffff8920e83770>] el0_svc_naked+0x24/0x28
> >
> >
> > And after this same crash occured:
> > [Â 325.521307] [<ffffff8920ed4aac>] smpboot_thread_fn+0x26c/0x2c8
> > [Â 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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