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kthread: Allow kthread_park() on a parked kthread

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The following commit:

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

added a WARN() in the case where we call kthread_park() on an already
parked thread, because the old code wasn't doing the right thing there
and it wasn't at all clear that would happen.

It turns out, this does in fact happen, so we have to deal with it.

Instead of potentially returning early, also wait for the completion.
This does however mean we have to use complete_all() and re-initialize
the completion on re-use.

Reported-by: LKP <[email protected]>
Tested-by: Meelis Roos <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: kernel test robot <[email protected]>
Cc: [email protected]
Cc: Thomas Gleixner <[email protected]>
Fixes: 85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() completion issue")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra authored and Ingo Molnar committed 2018-05-25 08:03:51 +02:00
1 parent bf5015a50f
commit b1f5b378e1
1 file changed
+2 -4
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kernel/kthread.c
+2 -4
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@@ -193,7 +193,7 @@ EXPORT_SYMBOL_GPL(kthread_parkme);
void kthread_park_complete(struct task_struct *k)
{
complete(&to_kthread(k)->parked);
complete_all(&to_kthread(k)->parked);
}
static int kthread(void *_create)
@@ -459,6 +459,7 @@ void kthread_unpark(struct task_struct *k)
if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
__kthread_bind(k, kthread->cpu, TASK_PARKED);
reinit_completion(&kthread->parked);
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
wake_up_state(k, TASK_PARKED);
}
@@ -483,9 +484,6 @@ int kthread_park(struct task_struct *k)
if (WARN_ON(k->flags & PF_EXITING))
return -ENOSYS;
if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
return -EBUSY;
set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
if (k != current) {
wake_up_process(k);