linux-kernel - Re: [RFC PATCH 1/3] timer: make try_to_del_timer_sync() safe on both hardirq context and UP

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Date:	Wed, 25 Aug 2010 21:21:50 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, mingo@...e.hu, peterz@...radead.org
Subject: Re: [RFC PATCH 1/3] timer: make try_to_del_timer_sync() safe on
 both hardirq context and UP

Oops, web sending break the thread.

Maybe I should show this change in V2.
coming soon.

-Yong

On Wed, Aug 25, 2010 at 02:26:12PM +0800, Yong Zhang wrote:
> From: Yong Zhang <yong.zhang@...driver.com>
> 
> In commit fd450b7318b75343fd76b3d95416853e34e72c95, it was saying
> try_to_del_timer_sync() can be used in interrupt context.
> 
> But because base->running_timer is SMP special, this lead to
> unsymmetry try_to_del_timer_sync() on UP and SMP.
> 
> We can make running_timer live on everywhere, then try_to_del_timer_sync()
> is also UP safe and can be used in hardirq context.
> 
> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Oleg Nesterov <oleg@...hat.com>
> ---
>  include/linux/timer.h |    4 ++--
>  kernel/timer.c        |    6 +-----
>  2 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/timer.h b/include/linux/timer.h
> index 38cf093..225c4ce 100644
> --- a/include/linux/timer.h
> +++ b/include/linux/timer.h
> @@ -248,11 +248,11 @@ static inline void
> timer_stats_timer_clear_start_info(struct timer_list *timer)
> 
>  extern void add_timer(struct timer_list *timer);
> 
> +extern int try_to_del_timer_sync(struct timer_list *timer);
> +
>  #ifdef CONFIG_SMP
> -  extern int try_to_del_timer_sync(struct timer_list *timer);
>    extern int del_timer_sync(struct timer_list *timer);
>  #else
> -# define try_to_del_timer_sync(t)	del_timer(t)
>  # define del_timer_sync(t)		del_timer(t)
>  #endif
> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index 97bf05b..e031eb4 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -347,9 +347,7 @@ EXPORT_SYMBOL_GPL(set_timer_slack);
>  static inline void set_running_timer(struct tvec_base *base,
>  					struct timer_list *timer)
>  {
> -#ifdef CONFIG_SMP
>  	base->running_timer = timer;
> -#endif
>  }
> 
>  static void internal_add_timer(struct tvec_base *base, struct
> timer_list *timer)
> @@ -936,15 +934,12 @@ int del_timer(struct timer_list *timer)
>  }
>  EXPORT_SYMBOL(del_timer);
> 
> -#ifdef CONFIG_SMP
>  /**
>   * try_to_del_timer_sync - Try to deactivate a timer
>   * @timer: timer do del
>   *
>   * This function tries to deactivate a timer. Upon successful (ret >= 0)
>   * exit the timer is not queued and the handler is not running on any CPU.
> - *
> - * It must not be called from interrupt contexts.
>   */
>  int try_to_del_timer_sync(struct timer_list *timer)
>  {
> @@ -973,6 +968,7 @@ out:
>  }
>  EXPORT_SYMBOL(try_to_del_timer_sync);
> 
> +#ifdef CONFIG_SMP
>  /**
>   * del_timer_sync - deactivate a timer and wait for the handler to finish.
>   * @timer: the timer to be deactivated
> -- 
> 1.7.0.4
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