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From: Greg KH on 11 Aug 2010 20:10
2.6.32-stable review patch. If anyone has any objections, please let us know.

------------------

From: Hidetoshi Seto <seto.hidetoshi(a)jp.fujitsu.com>

commit 761b1d26df542fd5eb348837351e4d2f3bc7bffe upstream.

Originally task_s/utime() were designed to return clock_t but
later changed to return cputime_t by following commit:

commit efe567fc8281661524ffa75477a7c4ca9b466c63
Author: Christian Borntraeger <borntraeger(a)de.ibm.com>
Date: Thu Aug 23 15:18:02 2007 +0200

It only changed the type of return value, but not the
implementation. As the result the granularity of task_s/utime()
is still that of clock_t, not that of cputime_t.

So using task_s/utime() in __exit_signal() makes values
accumulated to the signal struct to be rounded and coarse
grained.

This patch removes casts to clock_t in task_u/stime(), to keep
granularity of cputime_t over the calculation.

v2:
Use div_u64() to avoid error "undefined reference to `__udivdi3`"
on some 32bit systems.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi(a)jp.fujitsu.com>
Acked-by: Peter Zijlstra <peterz(a)infradead.org>
Cc: xiyou.wangcong(a)gmail.com
Cc: Spencer Candland <spencer(a)bluehost.com>
Cc: Oleg Nesterov <oleg(a)redhat.com>
Cc: Stanislaw Gruszka <sgruszka(a)redhat.com>
LKML-Reference: <4AFB9029.9000208(a)jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo(a)elte.hu>
Signed-off-by: Jiri Slaby <jslaby(a)suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
kernel/sched.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5216,41 +5216,45 @@ cputime_t task_stime(struct task_struct
return p->stime;
}
#else
+
+#ifndef nsecs_to_cputime
+# define nsecs_to_cputime(__nsecs) \
+ msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))
+#endif
+
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);
+ cputime_t utime = p->utime, total = utime + p->stime;
u64 temp;

/*
* Use CFS's precise accounting:
*/
- temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
+ temp = (u64)nsecs_to_cputime(p->se.sum_exec_runtime);

if (total) {
temp *= utime;
do_div(temp, total);
}
- utime = (clock_t)temp;
+ utime = (cputime_t)temp;

- p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
+ p->prev_utime = max(p->prev_utime, utime);
return p->prev_utime;
}

cputime_t task_stime(struct task_struct *p)
{
- clock_t stime;
+ cputime_t stime;

/*
* Use CFS's precise accounting. (we subtract utime from
* 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) -
- cputime_to_clock_t(task_utime(p));
+ stime = nsecs_to_cputime(p->se.sum_exec_runtime) - task_utime(p);

if (stime >= 0)
- p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+ p->prev_stime = max(p->prev_stime, stime);

return p->prev_stime;
}


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