[patch 10/13] sched: keep utime/stime monotonic

[Greg KH]

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

------------------
From: Frans Pop <elendil@xxxxxxxxx>

sched: keep utime/stime monotonic

cpustats use utime/stime as a ratio against sum_exec_runtime, as a
consequence it can happen - when the ratio changes faster than time
accumulates - that either can be appear to go backwards.

Combined backport for 2.6.23 of the following patches from mainline:
commit 73a2bcb0edb9ffb0b007b3546b430e2c6e415eee
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
  sched: keep utime/stime monotonic

commit 9301899be75b464ef097f0b5af7af6d9bd8f68a7
Author: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
  sched: fix /proc/<PID>/stat stime/utime monotonicity, part 2

Signed-off-by: Frans Pop <elendil@xxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/proc/array.c       |    6 ++++--
 include/linux/sched.h |    1 +
 kernel/fork.c         |    2 ++
 3 files changed, 7 insertions(+), 2 deletions(-)

--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -351,7 +351,8 @@ static cputime_t task_utime(struct task_
 	}
 	utime = (clock_t)temp;
 
-	return clock_t_to_cputime(utime);
+	p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
+	return p->prev_utime;
 }
 
 static cputime_t task_stime(struct task_struct *p)
@@ -366,7 +367,8 @@ static cputime_t task_stime(struct task_
 	stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
 			cputime_to_clock_t(task_utime(p));
 
-	return clock_t_to_cputime(stime);
+	p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+	return p->prev_stime;
 }
 #endif
 
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1022,6 +1022,7 @@ struct task_struct {
 
 	unsigned int rt_priority;
 	cputime_t utime, stime;
+	cputime_t prev_utime, prev_stime;
 	unsigned long nvcsw, nivcsw; /* context switch counts */
 	struct timespec start_time; 		/* monotonic time */
 	struct timespec real_start_time;	/* boot based time */
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1045,6 +1045,8 @@ static struct task_struct *copy_process(
 
 	p->utime = cputime_zero;
 	p->stime = cputime_zero;
+	p->prev_utime = cputime_zero;
+	p->prev_stime = cputime_zero;
 
 #ifdef CONFIG_TASK_XACCT
 	p->rchar = 0;		/* I/O counter: bytes read */

-- 
-
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