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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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4
include/linux/sched.h
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@@ -1475,6 +1475,10 @@ static inline void put_task_struct(struct task_struct *t)
__put_task_struct(t);
}
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);
/*
* Per process flags
*/