netdev - Re: [patch V3 14/17] timers: Add shutdown mechanism to the internal functions

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Message-ID: <d68c67a2-6488-89e9-4e56-e6efdb1260f@linutronix.de>
Date:   Thu, 24 Nov 2022 14:48:01 +0100 (CET)
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Arnd Bergmann <arnd@...db.de>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-bluetooth@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [patch V3 14/17] timers: Add shutdown mechanism to the internal
 functions

On Wed, 23 Nov 2022, Thomas Gleixner wrote:

> Tearing down timers which have circular dependencies to other
> functionality, e.g. workqueues, where the timer can schedule work and work
> can arm timers, is not trivial.
> 
> In those cases it is desired to shutdown the timer in a way which prevents
> rearming of the timer. The mechanism to do so is to set timer->function to
> NULL and use this as an indicator for the timer arming functions to ignore
> the (re)arm request.
> 
> Add a shutdown argument to the relevant internal functions which makes the
> actual deactivation code set timer->function to NULL which in turn prevents
> rearming of the timer.
> 
> Co-developed-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Guenter Roeck <linux@...ck-us.net>
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home
> Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org
> ---
> V2: Add missing commata (Steven)
> V3: Changelog updates (Anna-Maria)
> ---
>  kernel/time/timer.c |   64 ++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 55 insertions(+), 9 deletions(-)
> 
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1297,14 +1297,21 @@ void add_timer_on(struct timer_list *tim
>  EXPORT_SYMBOL_GPL(add_timer_on);
>  
>  /**
> - * __timer_delete - Internal function: Deactivate a timer.
> + * __timer_delete - Internal function: Deactivate a timer

Some more NIT: You already updated the line a patch before. Maybe remove
the dot in the patch before and you get rid of this unneccessary
delete/insert of the above line in this hunk.

>   * @timer:	The timer to be deactivated
> + * @shutdown:	If true, this indicates that the timer is about to be
> + *		shutdown permanently.
> + *
> + * If @shutdown is true then @timer->function is set to NULL under the
> + * timer base lock which prevents further rearming of the time. In that
> + * case any attempt to rearm @timer after this function returns will be
> + * silently ignored.
>   *
>   * Return:
>   * * %0 - The timer was not pending
>   * * %1 - The timer was pending and deactivated
>   */
> -static int __timer_delete(struct timer_list *timer)
> +static int __timer_delete(struct timer_list *timer, bool shutdown)
>  {
>  	struct timer_base *base;
>  	unsigned long flags;

Thanks,

	Anna-Maria