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| author | Frederic Weisbecker <frederic@kernel.org> | 2019-08-20 15:12:23 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-08-20 22:05:46 +0200 |
| commit | 0bee3b601b77dbe7981b5474ae8758d6bf60177a (patch) | |
| tree | bb5c920be193be0a68973d54969868b680e8ab9f /kernel/time/posix-timers.c | |
| parent | posix-timers: Use a callback for cancel synchronization on PREEMPT_RT (diff) | |
| download | linux-0bee3b601b77dbe7981b5474ae8758d6bf60177a.tar.xz linux-0bee3b601b77dbe7981b5474ae8758d6bf60177a.zip | |
hrtimer: Improve comments on handling priority inversion against softirq kthread
The handling of a priority inversion between timer cancelling and a a not
well defined possible preemption of softirq kthread is not very clear.
Especially in the posix timers side it's unclear why there is a specific RT
wait callback.
All the nice explanations can be found in the initial changelog of
f61eff83cec9 (hrtimer: Prepare support for PREEMPT_RT").
Extract the detailed informations from there and put it into comments.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190820132656.GC2093@lenoir
Diffstat (limited to 'kernel/time/posix-timers.c')
| -rw-r--r-- | kernel/time/posix-timers.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 9e377830cc10..0ec5b7a1d769 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -810,6 +810,12 @@ static void common_timer_wait_running(struct k_itimer *timer) hrtimer_cancel_wait_running(&timer->it.real.timer); } +/* + * On PREEMPT_RT this prevent priority inversion against softirq kthread in + * case it gets preempted while executing a timer callback. See comments in + * hrtimer_cancel_wait_running. For PREEMPT_RT=n this just results in a + * cpu_relax(). + */ static struct k_itimer *timer_wait_running(struct k_itimer *timer, unsigned long *flags) { |