linux-kernel - [tip: timers/core] timer: Improve the comment describing schedule

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Date:   Mon, 17 Feb 2020 19:18:45 -0000
From:   "tip-bot2 for Alexander Popov" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Alexander Popov <alex.popov@...ux.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: timers/core] timer: Improve the comment describing schedule_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 <alex.popov@...ux.com>
AuthorDate:    Sat, 18 Jan 2020 01:59:00 +03:00
Committer:     Thomas Gleixner <tglx@...utronix.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@...ux.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.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)