Explain it better and add the CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y aspect
for completeness.
Signed-off-by: Thomas Gleixner <[email protected]>
---
kernel/time/posix-timers.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -835,10 +835,18 @@ static void common_timer_wait_running(st
}
/*
- * 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)
On Tue, Apr 25, 2023 at 08:49:00PM +0200, Thomas Gleixner wrote:
> Explain it better and add the CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y aspect
> for completeness.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
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 <[email protected]>
AuthorDate: Tue, 25 Apr 2023 20:49:00 +02:00
Committer: Thomas Gleixner <[email protected]>
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 <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
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)
The following commit has been merged into the timers/core branch of tip:
Commit-ID: 7d9909026645064cd31b20cee5939a0f72282261
Gitweb: https://git.kernel.org/tip/7d9909026645064cd31b20cee5939a0f72282261
Author: Thomas Gleixner <[email protected]>
AuthorDate: Tue, 25 Apr 2023 20:49:00 +02:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Sun, 18 Jun 2023 22:41:48 +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 <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
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 2d6cf93..0c61f29 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)