[PATCH 2/2] time: xtime lock vs printk

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: time-printk-vs-xtime.patch --]
[-- Type: text/plain, Size: 926 bytes --]

This printk() can deadlock because it can wake up klogd(), and
task enqueueing will try to read the time in order to set a hrtimer.

Use the new printk_nowakeup() which will avoid waking klogd.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 kernel/time/timekeeping.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6-2/kernel/time/timekeeping.c
===================================================================
--- linux-2.6-2.orig/kernel/time/timekeeping.c
+++ linux-2.6-2/kernel/time/timekeeping.c
@@ -191,7 +191,11 @@ static void change_clocksource(void)
 
 	tick_clock_notify();
 
-	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
+	/*
+	 * We're holding xtime lock and waking up klogd would deadlock
+	 * us on enqueue. Print without waking.
+	 */
+	printk_nowakeup(KERN_INFO "Time: %s clocksource has been installed.\n",
 	       clock->name);
 }
 #else

--