Messages in this thread Patch in this message | | | From | Junaid Shahid <> | Subject | [PATCH] kthread: Fix race condition between kthread_parkme() and kthread_unpark() | Date | Fri, 28 Apr 2017 19:32:36 -0700 |
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In general, if kthread_unpark() and kthread_parkme() execute together, the kthread is supposed to be in an unparked state. This is because kthread_unpark() either wakes up the thread if it already got parked, or it cancels a prior kthread_park() call and hence renders the kthread_parkme() moot.
However, if kthread_unpark() happens to execute between the time that kthread_parkme() checks the KTHREAD_SHOULD_STOP flag and sets the KTHREAD_IS_PARKED flag, then kthread_unpark() will not wake up the thread and it will remain in a parked state.
This is fixed by making the checking of KTHREAD_SHOULD_STOP and the setting of KTHREAD_IS_PARKED atomic via a cmpxchg inside kthread_parkme.
Signed-off-by: Junaid Shahid <junaids@google.com> --- kernel/kthread.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c index 26db528c1d88..651f03baf62f 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -169,12 +169,20 @@ void *kthread_probe_data(struct task_struct *task) static void __kthread_parkme(struct kthread *self) { + ulong flags; + __set_current_state(TASK_PARKED); - while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) { - if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags)) - complete(&self->parked); - schedule(); + flags = self->flags; + + while (test_bit(KTHREAD_SHOULD_PARK, &flags)) { + if (cmpxchg(&self->flags, flags, + flags | (1 << KTHREAD_IS_PARKED)) == flags) { + if (!test_bit(KTHREAD_IS_PARKED, &flags)) + complete(&self->parked); + schedule(); + } __set_current_state(TASK_PARKED); + flags = self->flags; } clear_bit(KTHREAD_IS_PARKED, &self->flags); __set_current_state(TASK_RUNNING); -- 2.13.0.rc0.306.g87b477812d-goog
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