[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 0dc757246d89b02c96593df44ff8d75acb93e711..0c5ebf59b8bca559f9d15b849dc1944bd257810c 100644 (file)
--- 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;