Don't 'printk()' while holding xtime lock for writing

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

Reported-by: Marcin Slusarz <[e-mail]>
Debugged-by: Peter Zijlstra <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/time/timekeeping.c

···
 
 	tick_clock_notify();
 
+	/*
+	 * We're holding xtime lock and waking up klogd would deadlock
+	 * us on enqueue.  So no printing!
 	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
 	       clock->name);
+	 */
 }
 #else
 static inline void change_clocksource(void) { }