Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

[Ben Hutchings]

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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.

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

--- 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.

-- 
Ben Hutchings
73.46% of all statistics are made up.

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Re: Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

[Mike Galbraith]

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.
> 

Re: Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

[Mike Galbraith]

(CCs stable -rt maintainer)

On Sun, 2014-06-22 at 06:10 +0200, Mike Galbraith wrote: 
> 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.
> > 
> 
> 

Re: Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

[Carsten Emde]

On 06/22/2014 06:24 AM, Mike Galbraith wrote:
> [..]
> On Sun, 2014-06-22 at 06:10 +0200, Mike Galbraith wrote:
>> 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.
I can confirm that 3.12.22-rt34 systems with 
CONFIG_MISSED_TIMER_OFFSETS_HIST enabled crash at an early boot stage. 
After applying Ben's second patch proposal, all is back to normal.

>>
>>> --- 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:
Didn't use this one.

>>> --- 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?
Tested-by: Carsten Emde <C.Emde@osadl.org>

Thanks,
	-Carsten.