From 08e4570a4a393bcc241f78dfc444cb0b07995fc0 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 26 Nov 2007 21:21:49 +0100
Subject: [PATCH] sched: fix prev_stime calculation

Srivatsa Vaddagiri noticed occasionally incorrect CPU usage
values in top and tracked it down to stime going below 0 in
task_stime(). Negative values are possible there due to the
sampled nature of stime/utime.

Fix suggested by Balbir Singh.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
 fs/proc/array.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index eba339ecba27..65c62e1bfd6f 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -374,7 +374,9 @@ static cputime_t task_stime(struct task_struct *p)
 	stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
 			cputime_to_clock_t(task_utime(p));
 
-	p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+	if (stime >= 0)
+		p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+
 	return p->prev_stime;
 }
 #endif
-- 
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