The following commit has been merged into the timers/core branch of tip: Commit-ID: 07ca14d623d8b0e6c4a0d3de4ca8a8ea35a85470 Gitweb: https://git.kernel.org/tip/07ca14d623d8b0e6c4a0d3de4ca8a8ea35a85470 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Tue, 25 Apr 2023 20:49:00 +02:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Mon, 05 Jun 2023 17:03:37 +02:00 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@xxxxxxxxxxxxx> Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230425183312.985681995@xxxxxxxxxxxxx --- kernel/time/posix-timers.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 2c5daeb..4017533 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)
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