linux-kernel - Re: Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer

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Message-ID: <1403410224.5115.26.camel@marge.simpson.net>
Date:	Sun, 22 Jun 2014 06:10:24 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Carsten Emde <C.Emde@...dl.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Latency histogram broken after "hrtimer: Set expiry time before
 switch_hrtimer_base()"

On Sun, 2014-06-22 at 02:04 +0100, Ben Hutchings wrote: 
> In an rt-kernel with CONFIG_MISSED_TIMER_OFFSETS_HIST enabled,
> __hrtimer_start_range_ns() now crashes, as new_base is not assigned
> before it is used.

Oh yeah, forgot about this.

> I'm not sure how this should be fixed; is it:

My (3.12-ish tree) merge resolution was the later, but it shouldn't
matter which you choose, what's stored where is unchanged pre/post.

> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1108,7 +1108,7 @@ int __hrtimer_start_range_ns(struct hrti
>  
>  #ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
>  	{
> -		ktime_t now = new_base->get_time();
> +		ktime_t now = base->get_time();
>  
>  		if (ktime_to_ns(tim) < ktime_to_ns(now))
>  			timer->praecox = now;
> --- END ---
> 
> or:
> 
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1106,6 +1106,11 @@ int __hrtimer_start_range_ns(struct hrti
>  #endif
>  	}
>  
> +	hrtimer_set_expires_range_ns(timer, tim, delta_ns);
> +
> +	/* Switch the timer base, if necessary: */
> +	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
> +
>  #ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
>  	{
>  		ktime_t now = new_base->get_time();
> @@ -1117,11 +1122,6 @@ int __hrtimer_start_range_ns(struct hrti
>  	}
>  #endif
>  
> -	hrtimer_set_expires_range_ns(timer, tim, delta_ns);
> -
> -	/* Switch the timer base, if necessary: */
> -	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
> -
>  	timer_stats_hrtimer_set_start_info(timer);
>  
>  	leftmost = enqueue_hrtimer(timer, new_base);
> --- END ---
> 
> or something else?
> 
> Ben.
> 


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