Hi,
Has anyone been able to take a look at this?
Thanks,
Junaid
On Tuesday, May 30, 2017 03:40:02 PM Andrew Morton wrote:
> (cc tglx & tj)
>
> On Tue, 30 May 2017 15:37:23 -0700 Junaid Shahid <juna...@google.com> 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 <juna...@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);
> > >
