When we were preparing the patch 6dcd5d7a7a29c1e, we made a mistake noticed
by Linus: schedule_timeout() was called without setting the task state to
anything particular. It calls the scheduler, but doesn't delay anything,
because the task stays runnable. That happens because sched_submit_work()
does nothing for tasks in TASK_RUNNING state.
That turned out to be the intended behavior. Adding a WARN() is not useful.
Let's improve the comment about schedule_timeout() and describe that
more explicitly.
Signed-off-by: Alexander Popov <[email protected]>
---
kernel/time/timer.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4820823515e9..cb34fac9d9f7 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1828,21 +1828,23 @@ static void process_timeout(struct timer_list *t)
* schedule_timeout - sleep until timeout
* @timeout: timeout value in jiffies
*
- * Make the current task sleep until @timeout jiffies have
- * elapsed. The routine will return immediately unless
- * the current task state has been set (see set_current_state()).
+ * Make the current task sleep until @timeout jiffies have elapsed.
+ * The function behavior depends on the current task state
+ * (see also set_current_state() description):
*
- * You can set the task state as follows -
+ * %TASK_RUNNING - the scheduler is called, but the task does not sleep
+ * at all. That happens because sched_submit_work() does nothing for
+ * tasks in %TASK_RUNNING state.
*
* %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
* pass before the routine returns unless the current task is explicitly
- * woken up, (e.g. by wake_up_process())".
+ * woken up, (e.g. by wake_up_process()).
*
* %TASK_INTERRUPTIBLE - the routine may return early if a signal is
* delivered to the current task or the current task is explicitly woken
* up.
*
- * The current task state is guaranteed to be TASK_RUNNING when this
+ * The current task state is guaranteed to be %TASK_RUNNING when this
* routine returns.
*
* Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
@@ -1850,7 +1852,7 @@ static void process_timeout(struct timer_list *t)
* value will be %MAX_SCHEDULE_TIMEOUT.
*
* Returns 0 when the timer has expired otherwise the remaining time in
- * jiffies will be returned. In all cases the return value is guaranteed
+ * jiffies will be returned. In all cases the return value is guaranteed
* to be non-negative.
*/
signed long __sched schedule_timeout(signed long timeout)
--
2.24.1
Hello everyone!
Could I have any feedback for this patch?
Thanks!
On 18.01.2020 01:59, Alexander Popov wrote:
> When we were preparing the patch 6dcd5d7a7a29c1e, we made a mistake noticed
> by Linus: schedule_timeout() was called without setting the task state to
> anything particular. It calls the scheduler, but doesn't delay anything,
> because the task stays runnable. That happens because sched_submit_work()
> does nothing for tasks in TASK_RUNNING state.
>
> That turned out to be the intended behavior. Adding a WARN() is not useful.
> Let's improve the comment about schedule_timeout() and describe that
> more explicitly.
>
> Signed-off-by: Alexander Popov <[email protected]>
> ---
> kernel/time/timer.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 4820823515e9..cb34fac9d9f7 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1828,21 +1828,23 @@ static void process_timeout(struct timer_list *t)
> * schedule_timeout - sleep until timeout
> * @timeout: timeout value in jiffies
> *
> - * Make the current task sleep until @timeout jiffies have
> - * elapsed. The routine will return immediately unless
> - * the current task state has been set (see set_current_state()).
> + * Make the current task sleep until @timeout jiffies have elapsed.
> + * The function behavior depends on the current task state
> + * (see also set_current_state() description):
> *
> - * You can set the task state as follows -
> + * %TASK_RUNNING - the scheduler is called, but the task does not sleep
> + * at all. That happens because sched_submit_work() does nothing for
> + * tasks in %TASK_RUNNING state.
> *
> * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
> * pass before the routine returns unless the current task is explicitly
> - * woken up, (e.g. by wake_up_process())".
> + * woken up, (e.g. by wake_up_process()).
> *
> * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
> * delivered to the current task or the current task is explicitly woken
> * up.
> *
> - * The current task state is guaranteed to be TASK_RUNNING when this
> + * The current task state is guaranteed to be %TASK_RUNNING when this
> * routine returns.
> *
> * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
> @@ -1850,7 +1852,7 @@ static void process_timeout(struct timer_list *t)
> * value will be %MAX_SCHEDULE_TIMEOUT.
> *
> * Returns 0 when the timer has expired otherwise the remaining time in
> - * jiffies will be returned. In all cases the return value is guaranteed
> + * jiffies will be returned. In all cases the return value is guaranteed
> * to be non-negative.
> */
> signed long __sched schedule_timeout(signed long timeout)
>
The following commit has been merged into the timers/core branch of tip:
Commit-ID: 1b8020618b8922b9128b3015224221d0f869b471
Gitweb: https://git.kernel.org/tip/1b8020618b8922b9128b3015224221d0f869b471
Author: Alexander Popov <[email protected]>
AuthorDate: Sat, 18 Jan 2020 01:59:00 +03:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Mon, 17 Feb 2020 16:36:05 +01:00
timer: Improve the comment describing schedule_timeout()
When working commit 6dcd5d7a7a29c1e, a mistake was noticed by Linus:
schedule_timeout() was called without setting the task state to anything
particular.
It calls the scheduler, but doesn't delay anything, because the task stays
runnable. That happens because sched_submit_work() does nothing for tasks
in TASK_RUNNING state.
That turned out to be the intended behavior. Adding a WARN() is not useful
as the task could be woken up right after setting the state and before
reaching schedule_timeout().
Improve the comment about schedule_timeout() and describe that more
explicitly.
Signed-off-by: Alexander Popov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/time/timer.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4820823..cb34fac 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1828,21 +1828,23 @@ static void process_timeout(struct timer_list *t)
* schedule_timeout - sleep until timeout
* @timeout: timeout value in jiffies
*
- * Make the current task sleep until @timeout jiffies have
- * elapsed. The routine will return immediately unless
- * the current task state has been set (see set_current_state()).
+ * Make the current task sleep until @timeout jiffies have elapsed.
+ * The function behavior depends on the current task state
+ * (see also set_current_state() description):
*
- * You can set the task state as follows -
+ * %TASK_RUNNING - the scheduler is called, but the task does not sleep
+ * at all. That happens because sched_submit_work() does nothing for
+ * tasks in %TASK_RUNNING state.
*
* %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
* pass before the routine returns unless the current task is explicitly
- * woken up, (e.g. by wake_up_process())".
+ * woken up, (e.g. by wake_up_process()).
*
* %TASK_INTERRUPTIBLE - the routine may return early if a signal is
* delivered to the current task or the current task is explicitly woken
* up.
*
- * The current task state is guaranteed to be TASK_RUNNING when this
+ * The current task state is guaranteed to be %TASK_RUNNING when this
* routine returns.
*
* Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
@@ -1850,7 +1852,7 @@ static void process_timeout(struct timer_list *t)
* value will be %MAX_SCHEDULE_TIMEOUT.
*
* Returns 0 when the timer has expired otherwise the remaining time in
- * jiffies will be returned. In all cases the return value is guaranteed
+ * jiffies will be returned. In all cases the return value is guaranteed
* to be non-negative.
*/
signed long __sched schedule_timeout(signed long timeout)
The following commit has been merged into the timers/core branch of tip:
Commit-ID: 6e317c32fd39a13e4854a27958d5e35d15d196be
Gitweb: https://git.kernel.org/tip/6e317c32fd39a13e4854a27958d5e35d15d196be
Author: Alexander Popov <[email protected]>
AuthorDate: Sat, 18 Jan 2020 01:59:00 +03:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Mon, 17 Feb 2020 20:12:19 +01:00
timer: Improve the comment describing schedule_timeout()
When working commit 6dcd5d7a7a29c1e, a mistake was noticed by Linus:
schedule_timeout() was called without setting the task state to anything
particular.
It calls the scheduler, but doesn't delay anything, because the task stays
runnable. That happens because sched_submit_work() does nothing for tasks
in TASK_RUNNING state.
That turned out to be the intended behavior. Adding a WARN() is not useful
as the task could be woken up right after setting the state and before
reaching schedule_timeout().
Improve the comment about schedule_timeout() and describe that more
explicitly.
Signed-off-by: Alexander Popov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/time/timer.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4820823..cb34fac 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1828,21 +1828,23 @@ static void process_timeout(struct timer_list *t)
* schedule_timeout - sleep until timeout
* @timeout: timeout value in jiffies
*
- * Make the current task sleep until @timeout jiffies have
- * elapsed. The routine will return immediately unless
- * the current task state has been set (see set_current_state()).
+ * Make the current task sleep until @timeout jiffies have elapsed.
+ * The function behavior depends on the current task state
+ * (see also set_current_state() description):
*
- * You can set the task state as follows -
+ * %TASK_RUNNING - the scheduler is called, but the task does not sleep
+ * at all. That happens because sched_submit_work() does nothing for
+ * tasks in %TASK_RUNNING state.
*
* %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
* pass before the routine returns unless the current task is explicitly
- * woken up, (e.g. by wake_up_process())".
+ * woken up, (e.g. by wake_up_process()).
*
* %TASK_INTERRUPTIBLE - the routine may return early if a signal is
* delivered to the current task or the current task is explicitly woken
* up.
*
- * The current task state is guaranteed to be TASK_RUNNING when this
+ * The current task state is guaranteed to be %TASK_RUNNING when this
* routine returns.
*
* Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
@@ -1850,7 +1852,7 @@ static void process_timeout(struct timer_list *t)
* value will be %MAX_SCHEDULE_TIMEOUT.
*
* Returns 0 when the timer has expired otherwise the remaining time in
- * jiffies will be returned. In all cases the return value is guaranteed
+ * jiffies will be returned. In all cases the return value is guaranteed
* to be non-negative.
*/
signed long __sched schedule_timeout(signed long timeout)