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Peter Zijlstra 1cef1150ef kthread, sched/core: Fix kthread_parkme() (again...) 
Gaurav reports that commit:

  85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() completion issue")

isn't working for him. Because of the following race:

> 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

Furthermore, Oleg noticed that the whole scheduler TASK_PARKED
handling is buggered because the TASK_DEAD thing is done with
preemption disabled, the current code can still complete early on
preemption :/

So basically revert that earlier fix and go with a variant of the
alternative mentioned in the commit. Promote TASK_PARKED to special
state to avoid the store-store issue on task->state leading to the
WARN in kthread_unpark() -> __kthread_bind().

But in addition, add wait_task_inactive() to kthread_park() to ensure
the task really is PARKED when we return from kthread_park(). This
avoids the whole kthread still gets migrated nonsense -- although it
would be really good to get this done differently.

Reported-by: Gaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() completion issue")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 		2018-07-03 09:17:30 +02:00
..
Makefile
…
autogroup.c sched/autogroup: Fix possible Spectre-v1 indexing for sched_prio_to_weight[] 2018-05-05 08:34:42 +02:00
autogroup.h
…
clock.c
…
completion.c
…
core.c kthread, sched/core: Fix kthread_parkme() (again...) 2018-07-03 09:17:30 +02:00
cpuacct.c
…
cpudeadline.c
…
cpudeadline.h
…
cpufreq.c
…
cpufreq_schedutil.c sched/rt: Fix call to cpufreq_update_util() 2018-07-03 09:17:28 +02:00
cpupri.c
…
cpupri.h
…
cputime.c
…
deadline.c sched/deadline: Fix missing clock update 2018-05-31 12:27:13 +02:00
debug.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
fair.c sched/util_est: Fix util_est_dequeue() for throttled cfs_rq 2018-07-03 09:17:30 +02:00
features.h sched/fair: Update util_est only on util_avg updates 2018-03-20 08:11:09 +01:00
idle.c sched: idle: Select idle state before stopping the tick 2018-04-09 11:54:07 +02:00
isolation.c
…
loadavg.c
…
membarrier.c
…
rt.c sched/rt: Fix call to cpufreq_update_util() 2018-07-03 09:17:28 +02:00
sched-pelt.h
…
sched.h sched/fair: Fix bandwidth timer clock drift condition 2018-07-03 09:17:29 +02:00
stats.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
stats.h
…
stop_task.c
…
swait.c
…
topology.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
wait.c
…
wait_bit.c sched/wait: Improve __var_waitqueue() code generation 2018-03-20 08:23:25 +01:00