xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

kthread, sched/core: Fix kthread_parkme() (again...)

Browse Source 
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>
This commit is contained in:
Peter Zijlstra
2018-06-07 11:45:49 +02:00
committed by Ingo Molnar
parent 3482d98bbc
commit 1cef1150ef
4 changed files with 36 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
kernel/sched/core.c
View File

@@ -7,7 +7,6 @@
*/
#include "sched.h"
#include <linux/kthread.h>
#include <linux/nospec.h>
#include <linux/kcov.h>
@@ -2724,28 +2723,20 @@ static struct rq *finish_task_switch(struct task_struct *prev)
membarrier_mm_sync_core_before_usermode(mm);
mmdrop(mm);
}
if (unlikely(prev_state & (TASK_DEAD|TASK_PARKED))) {
switch (prev_state) {
case TASK_DEAD:
if (prev->sched_class->task_dead)
prev->sched_class->task_dead(prev);
if (unlikely(prev_state == TASK_DEAD)) {
if (prev->sched_class->task_dead)
prev->sched_class->task_dead(prev);
/*
* Remove function-return probe instances associated with this
* task and put them back on the free list.
*/
kprobe_flush_task(prev);
/*
* Remove function-return probe instances associated with this
* task and put them back on the free list.
*/
kprobe_flush_task(prev);
/* Task is done with its stack. */
put_task_stack(prev);
/* Task is done with its stack. */
put_task_stack(prev);
put_task_struct(prev);
break;
case TASK_PARKED:
kthread_park_complete(prev);
break;
}
put_task_struct(prev);
}
tick_nohz_task_switch();