Commit b1f5b378 authored May 04, 2018 by Peter Zijlstra Committed by Ingo Molnar May 25, 2018

kthread: Allow kthread_park() on a parked kthread



The following commit:

  85f1abe0 ("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 <lkp@01.org>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel test robot <lkp@intel.com>
Cc: wfg@linux.intel.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 85f1abe0 ("kthread, sched/wait: Fix kthread_parkme() completion issue")
Link: http://lkml.kernel.org/r/20180504091142.GI12235@hirez.programming.kicks-ass.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent bf5015a5

kernel/kthread.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -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);

Admin message