linux-kernel - Re: [PATCH] timer: Fix mod_timer_pinned() header commen (was: [PATCH RFC tip/core/rcu 4/4] rcu: Ensure that RCU_FAST_NO

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Date:	Thu, 26 Apr 2012 14:10:19 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH] timer: Fix mod_timer_pinned() header commen (was:
 [PATCH RFC tip/core/rcu 4/4] rcu: Ensure that RCU_FAST_NO_HZ timers expire
 on correct CPU)


> ------------------------------------------------------------------------
> 
> timer: Fix mod_timer_pinned() header comment
> 
> The mod_timer_pinned() header comment states that it prevents timers
> from being migrated to a different CPU.  This is not the case, instead,
> it ensures that the timer is posted to the current CPU, but does nothing
> to prevent CPU-hotplug operations from migrating the timer.
> 
> This commit therefore brings the comment header into alignment with
> reality.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

I'm seeing double :-)

> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index a297ffc..7114336 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -861,7 +861,12 @@ EXPORT_SYMBOL(mod_timer);
>   *
>   * mod_timer_pinned() is a way to update the expire field of an
>   * active timer (if the timer is inactive it will be activated)
> - * and not allow the timer to be migrated to a different CPU.
> + * and to ensure that the timer is scheduled on the current CPU.

Add space here.

  + *

> + * Note that this does not prevent the timer from being migrated
> + * when the current CPU goes offline.  If this is a problem for
> + * you, use CPU-hotplug notifiers to handle it correctly, for
> + * example, cancelling the timer when the corresponding CPU goes
> + * offline.
>   *
>   * mod_timer_pinned(timer, expires) is equivalent to:
>   *

Adding a space will make the "Note" stand out more, and more likely seen
by people who use this function.

Other than that:

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve


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