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timer: Improve the comment describing schedule_timeout()

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When working commit 6dcd5d7a7a, 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
This commit is contained in:
Alexander Popov 2020-01-18 01:59:00 +03:00 committed by Thomas Gleixner
parent e876f0b69d
commit 6e317c32fd
1 changed files with 9 additions and 7 deletions
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16
kernel/time/timer.c
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@ -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)