Messages in this thread Patch in this message | | | Date | Fri, 12 May 2023 00:31:24 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/wait: Fix a kthread_park race with wait_woken() |
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On Thu, May 11, 2023 at 09:41:30PM +0000, John Stultz wrote: > From: Arve Hjønnevåg <arve@android.com> > > kthread_park and wait_woken have a similar race that kthread_stop and > wait_woken used to have before it was fixed in > cb6538e740d7543cd989128625cf8cac4b471e0a. Extend that fix to also cover
cb6538e740d7 ("sched/wait: Fix a kthread race with wait_woken()")
> kthread_park. > > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Juri Lelli <juri.lelli@redhat.com> > Cc: Vincent Guittot <vincent.guittot@linaro.org> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Ben Segall <bsegall@google.com> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Cc: Valentin Schneider <vschneid@redhat.com> > Signed-off-by: Arve Hjønnevåg <arve@android.com> > Signed-off-by: John Stultz <jstultz@google.com> > --- > This seemingly slipped by, so I wanted to resend it > for review. > --- > kernel/sched/wait.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c > index 133b74730738..a9cf49da884b 100644 > --- a/kernel/sched/wait.c > +++ b/kernel/sched/wait.c > @@ -425,9 +425,9 @@ int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, i > } > EXPORT_SYMBOL(autoremove_wake_function); > > -static inline bool is_kthread_should_stop(void) > +static inline bool is_kthread_should_stop_or_park(void) > { > - return (current->flags & PF_KTHREAD) && kthread_should_stop(); > + return (current->flags & PF_KTHREAD) && (kthread_should_stop() || kthread_should_park()); > } > > /*
That's a bit sad; that two function calls for checking two consecutive bits in the same word :-(
If we move this to kthread.c and write it like:
kthread = __to_kthread(current); if (!kthread) return false;
return test_bit(KTHREAD_SHOULD_STOP, &kthread->flags) || test_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
Then the compiler should be able to merge the two bits in a single load and test due to constant_test_bit() -- do check though.
> @@ -459,7 +459,7 @@ long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) > * or woken_wake_function() sees our store to current->state. > */ > set_current_state(mode); /* A */ > - if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) > + if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop_or_park()) > timeout = schedule_timeout(timeout); > __set_current_state(TASK_RUNNING); > > -- > 2.40.1.606.ga4b1b128d6-goog >
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