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Subject[patch 5/7] posix-timers: Rework cancel retry loops
As a preparatory step for adding the PREEMPT RT specific synchronization
mechanism to wait for a running timer callback, rework the timer cancel
retry loops so they call a common function. This allows trivial
substitution in one place.

Originally-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/posix-timers.c | 29 +++++++++++++++++++++++------
1 file changed, 23 insertions(+), 6 deletions(-)

--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -805,6 +805,17 @@ static int common_hrtimer_try_to_cancel(
return hrtimer_try_to_cancel(&timr->it.real.timer);
}

+static struct k_itimer *timer_wait_running(struct k_itimer *timer,
+ unsigned long *flags)
+{
+ timer_t timer_id = READ_ONCE(timer->it_id);
+
+ unlock_timer(timer, *flags);
+ cpu_relax();
+ /* Relock the timer. It might be not longer hashed. */
+ return lock_timer(timer_id, flags);
+}
+
/* Set a POSIX.1b interval timer. */
int common_timer_set(struct k_itimer *timr, int flags,
struct itimerspec64 *new_setting,
@@ -859,8 +870,9 @@ static int do_timer_settime(timer_t time

if (old_spec64)
memset(old_spec64, 0, sizeof(*old_spec64));
-retry:
+
timr = lock_timer(timer_id, &flags);
+retry:
if (!timr)
return -EINVAL;

@@ -870,11 +882,14 @@ static int do_timer_settime(timer_t time
else
error = kc->timer_set(timr, tmr_flags, new_spec64, old_spec64);

- unlock_timer(timr, flags);
if (error == TIMER_RETRY) {
- old_spec64 = NULL; // We already got the old time...
+ // We already got the old time...
+ old_spec64 = NULL;
+ /* Unlocks and relocks the timer if it still exists */
+ timr = timer_wait_running(timr, &flags);
goto retry;
}
+ unlock_timer(timr, flags);

return error;
}
@@ -951,13 +966,15 @@ SYSCALL_DEFINE1(timer_delete, timer_t, t
struct k_itimer *timer;
unsigned long flags;

-retry_delete:
timer = lock_timer(timer_id, &flags);
+
+retry_delete:
if (!timer)
return -EINVAL;

- if (timer_delete_hook(timer) == TIMER_RETRY) {
- unlock_timer(timer, flags);
+ if (unlikely(timer_delete_hook(timer) == TIMER_RETRY)) {
+ /* Unlocks and relocks the timer if it still exists */
+ timer = timer_wait_running(timer, &flags);
goto retry_delete;
}


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