Commit 7d990902 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

posix-timers: Clarify timer_wait_running() comment 



Explain it better and add the CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y aspect
for completeness.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183312.985681995@linutronix.de
parent 8ce8849d

kernel/time/posix-timers.c

+12 −4
Original line number Diff line number Diff line
@@ -836,10 +836,18 @@ static void common_timer_wait_running(struct k_itimer *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().

 * On PREEMPT_RT this prevents priority inversion and a potential livelock

 * against the ksoftirqd thread in case that ksoftirqd gets preempted while

 * executing a hrtimer callback.

 *

 * See the comments in hrtimer_cancel_wait_running(). For PREEMPT_RT=n this

 * just results in a cpu_relax().

 *

 * For POSIX CPU timers with CONFIG_POSIX_CPU_TIMERS_TASK_WORK=n this is

 * just a cpu_relax(). With CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y this

 * prevents spinning on an eventually scheduled out task and a livelock

 * when the task which tries to delete or disarm the timer has preempted

 * the task which runs the expiry in task work context.

 */

static struct k_itimer *timer_wait_running(struct k_itimer *timer,

					   unsigned long *flags)