linux-kernel - [PATCH RT 2/3] initialize the clock source to jiffies clock.

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Date:	Fri, 24 Aug 2007 13:57:14 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>
Subject: [PATCH RT 2/3] initialize the clock source to jiffies clock.

The latency tracer can call clocksource_read very early in bootup and
before the clock source variable has been initialized. This results in a
crash at boot up (even before earlyprintk is initialized). Since the
clock->read variable is points to NULL.

This patch simply initializes the clock to use clocksource_jiffies, so
that any early user of clocksource_read will not crash.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Index: linux-2.6-rt/kernel/time/timekeeping.c
===================================================================
--- linux-2.6-rt.orig/kernel/time/timekeeping.c	2007-08-24 11:38:11.000000000 -0400
+++ linux-2.6-rt/kernel/time/timekeeping.c	2007-08-24 13:41:03.000000000 -0400
@@ -43,7 +43,15 @@ struct timespec wall_to_monotonic __attr
 EXPORT_SYMBOL(xtime);
 
 
-static struct clocksource *clock; /* pointer to current clocksource */
+extern struct clocksource clocksource_jiffies;
+
+/*
+ * pointer to current clocksource
+ *  Just in case we use clocksource_read before we initialize
+ *  the actual clock source. Instead of calling a NULL read pointer
+ *  we return jiffies.
+ */
+static struct clocksource *clock = &clocksource_jiffies;
 
 
 #ifdef CONFIG_GENERIC_TIME


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