sched: accounting regression since rc1

Fix the accounting regression for CONFIG_VIRT_CPU_ACCOUNTING.  It
reverts parts of commit b27f03d4bdc145a09fb7b0c0e004b29f1ee555fa by
converting fs/proc/array.c back to cputime_t.  The new functions
task_utime and task_stime now return cputime_t instead of clock_t.  If
CONFIG_VIRT_CPU_ACCOUTING is set, task->utime and task->stime are
returned directly instead of using sum_exec_runtime.

Patch is tested on s390x with and without VIRT_CPU_ACCOUTING as well as
on i386.

[ mingo@elte.hu: cleanups, comments. ]

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

fs/proc/array.c

@@ -320,7 +320,21 @@ int proc_pid_status(struct task_struct *task, char *buffer)
 	return buffer - orig;
 }
 
-static clock_t task_utime(struct task_struct *p)
+/*
+ * Use precise platform statistics if available:
+ */
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+static cputime_t task_utime(struct task_struct *p)
+{
+	return p->utime;
+}
+
+static cputime_t task_stime(struct task_struct *p)
+{
+	return p->stime;
+}
+#else
+static cputime_t task_utime(struct task_struct *p)
 {
 	clock_t utime = cputime_to_clock_t(p->utime),
 		total = utime + cputime_to_clock_t(p->stime);
@@ -337,10 +351,10 @@ static clock_t task_utime(struct task_struct *p)
 	}
 	utime = (clock_t)temp;
 
-	return utime;
+	return clock_t_to_cputime(utime);
 }
 
-static clock_t task_stime(struct task_struct *p)
+static cputime_t task_stime(struct task_struct *p)
 {
 	clock_t stime;
 
@@ -349,10 +363,12 @@ static clock_t task_stime(struct task_struct *p)
 	 * the total, to make sure the total observed by userspace
 	 * grows monotonically - apps rely on that):
 	 */
-	stime = nsec_to_clock_t(p->se.sum_exec_runtime) - task_utime(p);
+	stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
+			cputime_to_clock_t(task_utime(p));
 
-	return stime;
+	return clock_t_to_cputime(stime);
 }
+#endif
 
 static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 {
@@ -368,8 +384,7 @@ static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 	unsigned long long start_time;
 	unsigned long cmin_flt = 0, cmaj_flt = 0;
 	unsigned long  min_flt = 0,  maj_flt = 0;
-	cputime_t cutime, cstime;
-	clock_t utime, stime;
+	cputime_t cutime, cstime, utime, stime;
 	unsigned long rsslim = 0;
 	char tcomm[sizeof(task->comm)];
 	unsigned long flags;
@@ -387,8 +402,7 @@ static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 
 	sigemptyset(&sigign);
 	sigemptyset(&sigcatch);
-	cutime = cstime = cputime_zero;
-	utime = stime = 0;
+	cutime = cstime = utime = stime = cputime_zero;
 
 	rcu_read_lock();
 	if (lock_task_sighand(task, &flags)) {
@@ -414,15 +428,15 @@ static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 			do {
 				min_flt += t->min_flt;
 				maj_flt += t->maj_flt;
-				utime += task_utime(t);
-				stime += task_stime(t);
+				utime = cputime_add(utime, task_utime(t));
+				stime = cputime_add(stime, task_stime(t));
 				t = next_thread(t);
 			} while (t != task);
 
 			min_flt += sig->min_flt;
 			maj_flt += sig->maj_flt;
-			utime += cputime_to_clock_t(sig->utime);
-			stime += cputime_to_clock_t(sig->stime);
+			utime = cputime_add(utime, sig->utime);
+			stime = cputime_add(stime, sig->stime);
 		}
 
 		sid = signal_session(sig);
@@ -471,8 +485,8 @@ static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 		cmin_flt,
 		maj_flt,
 		cmaj_flt,
-		utime,
-		stime,
+		cputime_to_clock_t(utime),
+		cputime_to_clock_t(stime),
 		cputime_to_clock_t(cutime),
 		cputime_to_clock_t(cstime),
 		priority,