From: Peter Zijlstra Date: Fri, 4 May 2018 09:11:42 +0000 (+0200) Subject: kthread: Allow kthread_park() on a parked kthread X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=b1f5b378e126133521df668379249fb8265121f1;p=openwrt%2Fstaging%2Fblogic.git kthread: Allow kthread_park() on a parked kthread The following commit: 85f1abe0019f ("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 Tested-by: Meelis Roos Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: kernel test robot Cc: wfg@linux.intel.com Cc: Thomas Gleixner Fixes: 85f1abe0019f ("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 --- diff --git a/kernel/kthread.c b/kernel/kthread.c index 2017a39ab490..481951bf091d 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -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);