linux-kernel - Re: [PATCH 1/1] timer: Improve the comment describing schedule

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Date:   Sat, 8 Feb 2020 00:44:17 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     notify@...nel.org
Subject: Re: [PATCH 1/1] timer: Improve the comment describing
 schedule_timeout()

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@...ux.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)
>