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sched: fix process time monotonicity

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Spencer reported a problem where utime and stime were going negative despite
the fixes in commit b27f03d4bd. The suspected
reason for the problem is that signal_struct maintains it's own utime and
stime (of exited tasks), these are not updated using the new task_utime()
routine, hence sig->utime can go backwards and cause the same problem
to occur (sig->utime, adds tsk->utime and not task_utime()). This patch
fixes the problem

TODO: using max(task->prev_utime, derived utime) works for now, but a more
generic solution is to implement cputime_max() and use the cputime_gt()
function for comparison.

Reported-by: spencer@bluehost.com
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Balbir Singh
2008-09-05 18:12:23 +02:00
committed by Ingo Molnar
parent 56c7426b39
commit 49048622ea
4 changed files with 66 additions and 62 deletions
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59
fs/proc/array.c
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@@ -337,65 +337,6 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
return 0;
}
/*
* 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);
u64 temp;
/*
* Use CFS's precise accounting:
*/
temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
if (total) {
temp *= utime;
do_div(temp, total);
}
utime = (clock_t)temp;
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)
{
clock_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));
if (stime >= 0)
p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
return p->prev_stime;
}
#endif
static cputime_t task_gtime(struct task_struct *p)
{
return p->gtime;
}
static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task, int whole)
{