From ec8f954a40da8cd3d159713b608e901f0cd909a9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 2 Aug 2019 07:35:59 +0200 Subject: [PATCH] posix-timers: Use a callback for cancel synchronization on PREEMPT_RT 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 Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/20190819143801.656864506@linutronix.de --- kernel/time/alarmtimer.c | 14 ++++++++++++++ kernel/time/posix-timers.c | 18 +++++++++++++++++- kernel/time/posix-timers.h | 1 + 3 files changed, 32 insertions(+), 1 deletion(-) diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c index 36947449dba2..ec32876e284d 100644 --- a/kernel/time/alarmtimer.c +++ b/kernel/time/alarmtimer.c @@ -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 */ diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 3e663f982c82..9e377830cc10 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -805,13 +805,25 @@ static int common_hrtimer_try_to_cancel(struct k_itimer *timr) return hrtimer_try_to_cancel(&timr->it.real.timer); } +static void common_timer_wait_running(struct k_itimer *timer) +{ + hrtimer_cancel_wait_running(&timer->it.real.timer); +} + static struct k_itimer *timer_wait_running(struct k_itimer *timer, unsigned long *flags) { + const struct k_clock *kc = READ_ONCE(timer->kclock); timer_t timer_id = READ_ONCE(timer->it_id); + /* Prevent kfree(timer) after dropping the lock */ + rcu_read_lock(); unlock_timer(timer, *flags); - cpu_relax(); + + if (!WARN_ON_ONCE(!kc->timer_wait_running)) + kc->timer_wait_running(timer); + + rcu_read_unlock(); /* Relock the timer. It might be not longer hashed. */ return lock_timer(timer_id, flags); } @@ -1255,6 +1267,7 @@ static const struct k_clock clock_realtime = { .timer_forward = common_hrtimer_forward, .timer_remaining = common_hrtimer_remaining, .timer_try_to_cancel = common_hrtimer_try_to_cancel, + .timer_wait_running = common_timer_wait_running, .timer_arm = common_hrtimer_arm, }; @@ -1270,6 +1283,7 @@ static const struct k_clock clock_monotonic = { .timer_forward = common_hrtimer_forward, .timer_remaining = common_hrtimer_remaining, .timer_try_to_cancel = common_hrtimer_try_to_cancel, + .timer_wait_running = common_timer_wait_running, .timer_arm = common_hrtimer_arm, }; @@ -1300,6 +1314,7 @@ static const struct k_clock clock_tai = { .timer_forward = common_hrtimer_forward, .timer_remaining = common_hrtimer_remaining, .timer_try_to_cancel = common_hrtimer_try_to_cancel, + .timer_wait_running = common_timer_wait_running, .timer_arm = common_hrtimer_arm, }; @@ -1315,6 +1330,7 @@ static const struct k_clock clock_boottime = { .timer_forward = common_hrtimer_forward, .timer_remaining = common_hrtimer_remaining, .timer_try_to_cancel = common_hrtimer_try_to_cancel, + .timer_wait_running = common_timer_wait_running, .timer_arm = common_hrtimer_arm, }; diff --git a/kernel/time/posix-timers.h b/kernel/time/posix-timers.h index de5daa6d975a..897c29e162b9 100644 --- a/kernel/time/posix-timers.h +++ b/kernel/time/posix-timers.h @@ -24,6 +24,7 @@ struct k_clock { int (*timer_try_to_cancel)(struct k_itimer *timr); void (*timer_arm)(struct k_itimer *timr, ktime_t expires, bool absolute, bool sigev_none); + void (*timer_wait_running)(struct k_itimer *timr); }; extern const struct k_clock clock_posix_cpu;