[tip: timers/core] timer: Improve the comment describing schedule_timeout()
From: tip-bot2 for Alexander Popov
Date: Mon Feb 17 2020 - 10:40:55 EST
The following commit has been merged into the timers/core branch of tip:
Author: Alexander Popov <alex.popov@xxxxxxxxx>
AuthorDate: Sat, 18 Jan 2020 01:59:00 +03:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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
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
Improve the comment about schedule_timeout() and describe that more
Signed-off-by: Alexander Popov <alex.popov@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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
@@ -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
- * 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)