linux-kernel - Re: [RT PATCH 1/2] timers: wakeup all timer waiters

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Date:	Thu, 14 Jul 2016 12:13:41 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [RT PATCH 1/2] timers: wakeup all timer waiters

On Thu, 14 Jul 2016 18:05:03 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> The base lock is dropped during the invocation if the timer. That means
> it is possible that we have one waiter while timer1 is running and once
> this one finished, we get another waiter while timer2 is running. Since
> we wake up only one waiter it is possible that we miss the other one.
> This will probably heal itself over time because most of the time we
> complete timers without an active wake up.
> To avoid the scenario where we don't wake up all waiters at once,
> wake_up_all() is used.
> 
> Cc: stable-rt@...r.kernel.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/time/timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 5f9d3599ef0a..b3c3d3a6216f 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1051,7 +1051,7 @@ static void wait_for_running_timer(struct timer_list *timer)
>  		   base->running_timer != timer);
>  }
>  
> -# define wakeup_timer_waiters(b)	wake_up(&(b)->wait_for_running_timer)
> +# define wakeup_timer_waiters(b)	wake_up_all(&(b)->wait_for_running_timer)

OK, I just received this patch (way after patch 2)

I'm assuming that patch two was done such that you don't do a
"wake_up_all" under a spinlock.

-- Steve

>  #else
>  static inline void wait_for_running_timer(struct timer_list *timer)
>  {