[patch 23/26] NTP: remove clock_was_set() call to prevent deadlock

[Greg KH]

-stable review patch.  If anyone has any objections, please let us know.

------------------

The clock_was_set() call in seconds_overflow() which happens only when
leap seconds are inserted / deleted is wrong in two aspects:

1. it results in a call to on_each_cpu() with interrupts disabled
2. it is potential deadlock source vs. call_lock in smp_call_function()

The only possible side effect of the removal might be, that an absolute
CLOCK_REALTIME timer fires 1 second too late, in the rare case of leap
second deletion and an absolute CLOCK_REALTIME timer which expires in
the affected time frame. It will never fire too early.

This was probably observed by the reporter of a June 30th -> July 1st
hang: http://lkml.org/lkml/2007/7/3/

A similar problem was observed by Dave Jones, who provided a screen shot
with a lockdep back trace, which allowed to analyse the problem.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Vincent Fortier <Vincent.Fortier1@xxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/time/ntp.c |    2 --
 1 file changed, 2 deletions(-)

--- linux-2.6.21.6.orig/kernel/time/ntp.c
+++ linux-2.6.21.6/kernel/time/ntp.c
@@ -120,7 +120,6 @@ void second_overflow(void)
 			 */
 			time_interpolator_update(-NSEC_PER_SEC);
 			time_state = TIME_OOP;
-			clock_was_set();
 			printk(KERN_NOTICE "Clock: inserting leap second "
 					"23:59:60 UTC\n");
 		}
@@ -135,7 +134,6 @@ void second_overflow(void)
 			 */
 			time_interpolator_update(NSEC_PER_SEC);
 			time_state = TIME_WAIT;
-			clock_was_set();
 			printk(KERN_NOTICE "Clock: deleting leap second "
 					"23:59:59 UTC\n");
 		}

-- 
-
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