From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 1 Mar 2007 04:12:19 +0000 (-0800)
Subject: [PATCH] Fix posix-cpu-timer breakage caused by stale p->last_ran value
X-Git-Tag: v2.6.21-rc3~181
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c1e16aa2792a129d8920e22210ef21eb62a0f80a;p=linux-2.6

[PATCH] Fix posix-cpu-timer breakage caused by stale p->last_ran value

Problem description at:
http://bugzilla.kernel.org/show_bug.cgi?id=8048

Commit b18ec80396834497933d77b81ec0918519f4e2a7
    [PATCH] sched: improve migration accuracy
optimized the scheduler time calculations, but broke posix-cpu-timers.

The problem is that the p->last_ran value is not updated after a context
switch.  So a subsequent call to current_sched_time() calculates with a
stale p->last_ran value, i.e.  accounts the full time, which the task was
scheduled away.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/kernel/sched.c b/kernel/sched.c
index 0dc757246d..0c5ebf59b8 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3566,7 +3566,7 @@ switch_tasks:
 
 	sched_info_switch(prev, next);
 	if (likely(prev != next)) {
-		next->timestamp = now;
+		next->timestamp = next->last_ran = now;
 		rq->nr_switches++;
 		rq->curr = next;
 		++*switch_count;