sched: fix /proc/<PID>/stat stime/utime monotonicity, part 2

Extend Peter's patch to fix accounting issues, by keeping stime
monotonic too.
Signed-off-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Tested-by: NFrans Pop <elendil@planet.nl>

fs/proc/array.c

@@ -374,7 +374,8 @@ 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));
 
-	return clock_t_to_cputime(stime);
+	p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+	return p->prev_stime;
 }
 #endif
 

include/linux/sched.h

@@ -1009,7 +1009,7 @@ struct task_struct {
 	unsigned int rt_priority;
 	cputime_t utime, stime, utimescaled, stimescaled;
 	cputime_t gtime;
-	cputime_t prev_utime;
+	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 */

kernel/fork.c

@@ -1057,6 +1057,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	p->utimescaled = cputime_zero;
 	p->stimescaled = cputime_zero;
 	p->prev_utime = cputime_zero;
+	p->prev_stime = cputime_zero;
 
 #ifdef CONFIG_TASK_XACCT
 	p->rchar = 0;		/* I/O counter: bytes read */