(cc tglx & tj) On Tue, 30 May 2017 15:37:23 -0700 Junaid Shahid <[email protected]> wrote:
> (Resending) > > On Friday, April 28, 2017 07:32:36 PM Junaid Shahid wrote: > > 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 <[email protected]> > > --- > > 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); > >
