[PATCH] kernel/timer.c: xtime lock missing

[Benjamin LaHaise <bcrl@kvack.org>]

Hello all,

While looking at the time keeping code for related work, I came across 
the following bug.  During 2.5 development, the smptimers patch removed 
a lock from update_times() that is actually needed over the xtime 
update, since the second overflow is not an atomic operation.  This 
patch fixes that by doing a write_seqlock() over the course of the 
update.

		-ben
-- 
"Time is what keeps everything from happening all at once." -- John Wheeler

===== timer.c 1.93 vs edited =====
--- 1.93/kernel/timer.c	2004-09-17 03:07:06 -04:00
+++ edited/timer.c	2004-10-21 14:51:53 -04:00
@@ -940,11 +940,14 @@
 {
 	unsigned long ticks;
 
+	/* interrupts are disabled */
+	write_seqlock(&xtime_lock);
 	ticks = jiffies - wall_jiffies;
 	if (ticks) {
 		wall_jiffies += ticks;
 		update_wall_time(ticks);
 	}
+	write_sequnlock(&xtime_lock);
 	calc_load(ticks);
 }