linux-kernel - Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer

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Date:   Fri, 28 Oct 2022 16:40:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Bhuvanesh Surachari <Bhuvanesh_Surachari@...tor.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-usb@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        John Stultz <jstultz@...gle.com>
Subject: Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer_shutdown()
 before freeing timer

On Fri, 28 Oct 2022 12:59:59 -0700
Guenter Roeck <linux@...ck-us.net> wrote:
> 
> I'll test again with the following changes on top of your published
> patch series. I hope this is the current status, but I may have lost
> something.
> 
> Looking into it ... deactivate_timer() doesn't do anything 
> and seems wrong. Did I miss something ?

You mean debug_deactivate_timer() or debug_deactivate?


> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c


>  
> -static inline void debug_timer_deactivate(struct timer_list *timer)
> +static inline void debug_timer_deactivate(struct timer_list *timer, bool free)
>  {
> -	if (timer->enabled)
> -		debug_object_deactivate(timer, &timer_debug_descr);
> +	switch (timer->enabled) {
> +	case TIMER_DEBUG_DISABLED:

DISABLE is set before an activate happens (before it is ever armed).

> +		return;
> +	case TIMER_DEBUG_ENABLED:
> +		if (!free)
> +			return;

This is called by del_timer{,_sync}() where free is false, or
del_timer_shutdown() where free is true.

We only want to deactivate when free is true.

> +		timer->enabled = TIMER_DEBUG_DISABLED;

And we allow for initialization of a "freed" timer again.

> +		break;
> +	case TIMER_DEBUG_WORK:

This is part of the delayed_work timers, were we keep the old behavior
(del_timer() and del_timer_sync() both deactivate the timer.

> +		break;
> +	}
> +	debug_object_deactivate(timer, &timer_debug_descr);

Here we call the debug object code to deactivate it.

>  }
>  
>  static inline void debug_timer_assert_init(struct timer_list *timer)
> @@ -833,6 +854,7 @@ static inline void debug_init(struct timer_list *timer)
>  
>  static inline void debug_deactivate(struct timer_list *timer)
>  {
> +	debug_timer_deactivate(timer, false);

This calls the above code.

>  	trace_timer_cancel(timer);
>  }


Or am I confused and you meant something else?

-- Steve