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From: Greg KH on 11 Aug 2010 20:40
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 0cf55e1ec08bb5a22e068309e2d8ba1180ab4239 upstream.

This is a real fix for problem of utime/stime values decreasing
described in the thread:

http://lkml.org/lkml/2009/11/3/522

Now cputime is accounted in the following way:

- {u,s}time in task_struct are increased every time when the thread
is interrupted by a tick (timer interrupt).

- When a thread exits, its {u,s}time are added to signal->{u,s}time,
after adjusted by task_times().

- When all threads in a thread_group exits, accumulated {u,s}time
(and also c{u,s}time) in signal struct are added to c{u,s}time
in signal struct of the group's parent.

So {u,s}time in task struct are "raw" tick count, while
{u,s}time and c{u,s}time in signal struct are "adjusted" values.

And accounted values are used by:

- task_times(), to get cputime of a thread:
This function returns adjusted values that originates from raw
{u,s}time and scaled by sum_exec_runtime that accounted by CFS.

- thread_group_cputime(), to get cputime of a thread group:
This function returns sum of all {u,s}time of living threads in
the group, plus {u,s}time in the signal struct that is sum of
adjusted cputimes of all exited threads belonged to the group.

The problem is the return value of thread_group_cputime(),
because it is mixed sum of "raw" value and "adjusted" value:

group's {u,s}time = foreach(thread){{u,s}time} + exited({u,s}time)

This misbehavior can break {u,s}time monotonicity.
Assume that if there is a thread that have raw values greater
than adjusted values (e.g. interrupted by 1000Hz ticks 50 times
but only runs 45ms) and if it exits, cputime will decrease (e.g.
-5ms).

To fix this, we could do:

group's {u,s}time = foreach(t){task_times(t)} + exited({u,s}time)

But task_times() contains hard divisions, so applying it for
every thread should be avoided.

This patch fixes the above problem in the following way:

- Modify thread's exit (= __exit_signal()) not to use task_times().
It means {u,s}time in signal struct accumulates raw values instead
of adjusted values. As the result it makes thread_group_cputime()
to return pure sum of "raw" values.

- Introduce a new function thread_group_times(*task, *utime, *stime)
that converts "raw" values of thread_group_cputime() to "adjusted"
values, in same calculation procedure as task_times().

- Modify group's exit (= wait_task_zombie()) to use this introduced
thread_group_times(). It make c{u,s}time in signal struct to
have adjusted values like before this patch.

- Replace some thread_group_cputime() by thread_group_times().
This replacements are only applied where conveys the "adjusted"
cputime to users, and where already uses task_times() near by it.
(i.e. sys_times(), getrusage(), and /proc/<PID>/stat.)

This patch have a positive side effect:

- Before this patch, if a group contains many short-life threads
(e.g. runs 0.9ms and not interrupted by ticks), the group's
cputime could be invisible since thread's cputime was accumulated
after adjusted: imagine adjustment function as adj(ticks, runtime),
{adj(0, 0.9) + adj(0, 0.9) + ....} = {0 + 0 + ....} = 0.
After this patch it will not happen because the adjustment is
applied after accumulated.

v2:
- remove if()s, put new variables into signal_struct.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi(a)jp.fujitsu.com>
Acked-by: Peter Zijlstra <peterz(a)infradead.org>
Cc: Spencer Candland <spencer(a)bluehost.com>
Cc: Americo Wang <xiyou.wangcong(a)gmail.com>
Cc: Oleg Nesterov <oleg(a)redhat.com>
Cc: Balbir Singh <balbir(a)in.ibm.com>
Cc: Stanislaw Gruszka <sgruszka(a)redhat.com>
LKML-Reference: <4B162517.8040909(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>


---
fs/proc/array.c | 5 +----
include/linux/sched.h | 4 ++++
kernel/exit.c | 20 ++++++++++++--------
kernel/fork.c | 3 +++
kernel/sched.c | 41 +++++++++++++++++++++++++++++++++++++++++
kernel/sys.c | 18 ++++++++----------
6 files changed, 69 insertions(+), 22 deletions(-)

--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -405,7 +405,6 @@ static int do_task_stat(struct seq_file

/* add up live thread stats at the group level */
if (whole) {
- struct task_cputime cputime;
struct task_struct *t = task;
do {
min_flt += t->min_flt;
@@ -416,9 +415,7 @@ static int do_task_stat(struct seq_file

min_flt += sig->min_flt;
maj_flt += sig->maj_flt;
- thread_group_cputime(task, &cputime);
- utime = cputime.utime;
- stime = cputime.stime;
+ thread_group_times(task, &utime, &stime);
gtime = cputime_add(gtime, sig->gtime);
}

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -628,6 +628,9 @@ struct signal_struct {
cputime_t utime, stime, cutime, cstime;
cputime_t gtime;
cputime_t cgtime;
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING
+ cputime_t prev_utime, prev_stime;
+#endif
unsigned long nvcsw, nivcsw, cnvcsw, cnivcsw;
unsigned long min_flt, maj_flt, cmin_flt, cmaj_flt;
unsigned long inblock, oublock, cinblock, coublock;
@@ -1725,6 +1728,7 @@ static inline void put_task_struct(struc
extern cputime_t task_utime(struct task_struct *p);
extern cputime_t task_stime(struct task_struct *p);
extern cputime_t task_gtime(struct task_struct *p);
+extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st);

/*
* Per process flags
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -110,8 +110,8 @@ static void __exit_signal(struct task_st
* We won't ever get here for the group leader, since it
* will have been the last reference on the signal_struct.
*/
- sig->utime = cputime_add(sig->utime, task_utime(tsk));
- sig->stime = cputime_add(sig->stime, task_stime(tsk));
+ sig->utime = cputime_add(sig->utime, tsk->utime);
+ sig->stime = cputime_add(sig->stime, tsk->stime);
sig->gtime = cputime_add(sig->gtime, task_gtime(tsk));
sig->min_flt += tsk->min_flt;
sig->maj_flt += tsk->maj_flt;
@@ -1205,6 +1205,7 @@ static int wait_task_zombie(struct wait_
struct signal_struct *psig;
struct signal_struct *sig;
unsigned long maxrss;
+ cputime_t tgutime, tgstime;

/*
* The resource counters for the group leader are in its
@@ -1220,20 +1221,23 @@ static int wait_task_zombie(struct wait_
* need to protect the access to parent->signal fields,
* as other threads in the parent group can be right
* here reaping other children at the same time.
+ *
+ * We use thread_group_times() to get times for the thread
+ * group, which consolidates times for all threads in the
+ * group including the group leader.
*/
+ thread_group_times(p, &tgutime, &tgstime);
spin_lock_irq(&p->real_parent->sighand->siglock);
psig = p->real_parent->signal;
sig = p->signal;
psig->cutime =
cputime_add(psig->cutime,
- cputime_add(p->utime,
- cputime_add(sig->utime,
- sig->cutime)));
+ cputime_add(tgutime,
+ sig->cutime));
psig->cstime =
cputime_add(psig->cstime,
- cputime_add(p->stime,
- cputime_add(sig->stime,
- sig->cstime)));
+ cputime_add(tgstime,
+ sig->cstime));
psig->cgtime =
cputime_add(psig->cgtime,
cputime_add(p->gtime,
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -884,6 +884,9 @@ static int copy_signal(unsigned long clo
sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
sig->gtime = cputime_zero;
sig->cgtime = cputime_zero;
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING
+ sig->prev_utime = sig->prev_stime = cputime_zero;
+#endif
sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5215,6 +5215,16 @@ cputime_t task_stime(struct task_struct
{
return p->stime;
}
+
+void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
+{
+ struct task_cputime cputime;
+
+ thread_group_cputime(p, &cputime);
+
+ *ut = cputime.utime;
+ *st = cputime.stime;
+}
#else

#ifndef nsecs_to_cputime
@@ -5258,6 +5268,37 @@ cputime_t task_stime(struct task_struct

return p->prev_stime;
}
+
+/*
+ * Must be called with siglock held.
+ */
+void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
+{
+ struct signal_struct *sig = p->signal;
+ struct task_cputime cputime;
+ cputime_t rtime, utime, total;
+
+ thread_group_cputime(p, &cputime);
+
+ total = cputime_add(cputime.utime, cputime.stime);
+ rtime = nsecs_to_cputime(cputime.sum_exec_runtime);
+
+ if (total) {
+ u64 temp;
+
+ temp = (u64)(rtime * cputime.utime);
+ do_div(temp, total);
+ utime = (cputime_t)temp;
+ } else
+ utime = rtime;
+
+ sig->prev_utime = max(sig->prev_utime, utime);
+ sig->prev_stime = max(sig->prev_stime,
+ cputime_sub(rtime, sig->prev_utime));
+
+ *ut = sig->prev_utime;
+ *st = sig->prev_stime;
+}
#endif

inline cputime_t task_gtime(struct task_struct *p)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -911,16 +911,15 @@ change_okay:

void do_sys_times(struct tms *tms)
{
- struct task_cputime cputime;
- cputime_t cutime, cstime;
+ cputime_t tgutime, tgstime, cutime, cstime;

- thread_group_cputime(current, &cputime);
spin_lock_irq(&current->sighand->siglock);
+ thread_group_times(current, &tgutime, &tgstime);
cutime = current->signal->cutime;
cstime = current->signal->cstime;
spin_unlock_irq(&current->sighand->siglock);
- tms->tms_utime = cputime_to_clock_t(cputime.utime);
- tms->tms_stime = cputime_to_clock_t(cputime.stime);
+ tms->tms_utime = cputime_to_clock_t(tgutime);
+ tms->tms_stime = cputime_to_clock_t(tgstime);
tms->tms_cutime = cputime_to_clock_t(cutime);
tms->tms_cstime = cputime_to_clock_t(cstime);
}
@@ -1338,8 +1337,7 @@ static void k_getrusage(struct task_stru
{
struct task_struct *t;
unsigned long flags;
- cputime_t utime, stime;
- struct task_cputime cputime;
+ cputime_t tgutime, tgstime, utime, stime;
unsigned long maxrss = 0;

memset((char *) r, 0, sizeof *r);
@@ -1373,9 +1371,9 @@ static void k_getrusage(struct task_stru
break;

case RUSAGE_SELF:
- thread_group_cputime(p, &cputime);
- utime = cputime_add(utime, cputime.utime);
- stime = cputime_add(stime, cputime.stime);
+ thread_group_times(p, &tgutime, &tgstime);
+ utime = cputime_add(utime, tgutime);
+ stime = cputime_add(stime, tgstime);
r->ru_nvcsw += p->signal->nvcsw;
r->ru_nivcsw += p->signal->nivcsw;
r->ru_minflt += p->signal->min_flt;


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Next: [067/111] Btrfs: fix possible panic on unmount