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authorThomas Gleixner <tglx@linutronix.de>2023-04-25 20:49:00 +0200
committerThomas Gleixner <tglx@linutronix.de>2023-06-18 22:41:48 +0200
commit7d9909026645064cd31b20cee5939a0f72282261 (patch)
tree9440111cc1638de03565083ff20ad670691dcfc7 /kernel/time
parent8ce8849dd1e78dadcee0ec9acbd259d239b7069f (diff)
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: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20230425183312.985681995@linutronix.de
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/posix-timers.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 2d6cf93ca370..0c61f29ef5d5 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -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)