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* [PATCH 1/1] timer: Improve the comment describing schedule_timeout()
@ 2020-01-17 22:59 Alexander Popov
  2020-02-07 21:44 ` Alexander Popov
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Alexander Popov @ 2020-01-17 22:59 UTC (permalink / raw)
  To: Linus Torvalds, John Stultz, Thomas Gleixner, Stephen Boyd,
	Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Alexander Popov, linux-kernel
  Cc: notify

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 <alex.popov@linux.com>
---
 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


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH 1/1] timer: Improve the comment describing schedule_timeout()
  2020-01-17 22:59 [PATCH 1/1] timer: Improve the comment describing schedule_timeout() Alexander Popov
@ 2020-02-07 21:44 ` Alexander Popov
  2020-02-17 15:40 ` [tip: timers/core] " tip-bot2 for Alexander Popov
  2020-02-17 19:18 ` tip-bot2 for Alexander Popov
  2 siblings, 0 replies; 4+ messages in thread
From: Alexander Popov @ 2020-02-07 21:44 UTC (permalink / raw)
  To: Linus Torvalds, John Stultz, Thomas Gleixner, Stephen Boyd,
	Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	linux-kernel
  Cc: notify

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 <alex.popov@linux.com>
> ---
>  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)
> 


^ permalink raw reply	[flat|nested] 4+ messages in thread

* [tip: timers/core] timer: Improve the comment describing schedule_timeout()
  2020-01-17 22:59 [PATCH 1/1] timer: Improve the comment describing schedule_timeout() Alexander Popov
  2020-02-07 21:44 ` Alexander Popov
@ 2020-02-17 15:40 ` " tip-bot2 for Alexander Popov
  2020-02-17 19:18 ` tip-bot2 for Alexander Popov
  2 siblings, 0 replies; 4+ messages in thread
From: tip-bot2 for Alexander Popov @ 2020-02-17 15:40 UTC (permalink / raw)
  To: linux-tip-commits; +Cc: Alexander Popov, Thomas Gleixner, x86, LKML

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 <alex.popov@linux.com>
AuthorDate:    Sat, 18 Jan 2020 01:59:00 +03:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
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 <alex.popov@linux.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200117225900.16340-1-alex.popov@linux.com

---
 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)

^ permalink raw reply	[flat|nested] 4+ messages in thread

* [tip: timers/core] timer: Improve the comment describing schedule_timeout()
  2020-01-17 22:59 [PATCH 1/1] timer: Improve the comment describing schedule_timeout() Alexander Popov
  2020-02-07 21:44 ` Alexander Popov
  2020-02-17 15:40 ` [tip: timers/core] " tip-bot2 for Alexander Popov
@ 2020-02-17 19:18 ` tip-bot2 for Alexander Popov
  2 siblings, 0 replies; 4+ messages in thread
From: tip-bot2 for Alexander Popov @ 2020-02-17 19:18 UTC (permalink / raw)
  To: linux-tip-commits; +Cc: Alexander Popov, Thomas Gleixner, x86, LKML

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 <alex.popov@linux.com>
AuthorDate:    Sat, 18 Jan 2020 01:59:00 +03:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
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 <alex.popov@linux.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200117225900.16340-1-alex.popov@linux.com


---
 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)

^ permalink raw reply	[flat|nested] 4+ messages in thread

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2020-01-17 22:59 [PATCH 1/1] timer: Improve the comment describing schedule_timeout() Alexander Popov
2020-02-07 21:44 ` Alexander Popov
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2020-02-17 19:18 ` tip-bot2 for Alexander Popov

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