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

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Date:	Sun, 22 Jun 2014 02:04:25 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Carsten Emde <C.Emde@...dl.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Latency histogram broken after "hrtimer: Set expiry time before
 switch_hrtimer_base()"

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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