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posix-timers: Use a callback for cancel synchronization on PREEMPT_RT

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Posix timer delete retry loops are affected by the same priority inversion
and live lock issues as the other timers.
    
Provide a RT specific synchronization function which keeps a reference to
the timer by holding rcu read lock to prevent the timer from being freed,
dropping the timer lock and invoking the timer specific wait function via a
new callback.
    
This does not yet cover posix CPU timers because they need more special
treatment on PREEMPT_RT.

[ This is folded into the original attempt which did not use a callback. ]

Originally-by: Anna-Maria Gleixenr <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190819143801.656864506@linutronix.de
This commit is contained in:
Thomas Gleixner 2019-08-02 07:35:59 +02:00
parent 5d99b32a00
commit ec8f954a40
3 changed files with 32 additions and 1 deletions
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14
kernel/time/alarmtimer.c
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@ -605,6 +605,19 @@ static int alarm_timer_try_to_cancel(struct k_itimer *timr)
return alarm_try_to_cancel(&timr->it.alarm.alarmtimer);
}
/**
* alarm_timer_wait_running - Posix timer callback to wait for a timer
* @timr: Pointer to the posixtimer data struct
*
* Called from the core code when timer cancel detected that the callback
* is running. @timr is unlocked and rcu read lock is held to prevent it
* from being freed.
*/
static void alarm_timer_wait_running(struct k_itimer *timr)
{
hrtimer_cancel_wait_running(&timr->it.alarm.alarmtimer.timer);
}
/**
* alarm_timer_arm - Posix timer callback to arm a timer
* @timr: Pointer to the posixtimer data struct
@ -834,6 +847,7 @@ const struct k_clock alarm_clock = {
.timer_forward = alarm_timer_forward,
.timer_remaining = alarm_timer_remaining,
.timer_try_to_cancel = alarm_timer_try_to_cancel,
.timer_wait_running = alarm_timer_wait_running,
.nsleep = alarm_timer_nsleep,
};
#endif /* CONFIG_POSIX_TIMERS */