Re: sched/cputime: sig->prev_stime underflow

[Stanislaw Gruszka]

On Tue, Apr 16, 2013 at 02:05:22PM -0700, Dave Hansen wrote:
> > But since this (most likely) is rtime monotonicity problem it
> > is bug by itself and probably that should be fixed. Can you 
> > check second patch attached and see if it trigger the warning.
> 
> Yup, it triggers lots of warnings.  Here's one.
> 
> > [  460.789710] ------------[ cut here ]------------
> > [  460.789730] WARNING: at /home/davehans/linux.git/kernel/sched/cputime.c:563 cputime_adjust+0xe6/0xf0()
> > [  460.789736] Hardware name: PRIMEQUEST 1800E2
> > [  460.789739] Modules linked in:
> > [  460.789745] Pid: 4245, comm: top Tainted: G        W    3.9.0-rc7-00004-gbb33db7-dirty #19
> > [  460.789748] Call Trace:
> > [  460.789777]  [<ffffffff810c6dc7>] warn_slowpath_common+0xb7/0x120
> > [  460.789783]  [<ffffffff810c6e5a>] warn_slowpath_null+0x2a/0x40
> > [  460.789789]  [<ffffffff8111a8d6>] cputime_adjust+0xe6/0xf0
> > [  460.789795]  [<ffffffff8111b755>] ? thread_group_cputime+0x5/0x140
> > [  460.789800]  [<ffffffff8111bbb9>] thread_group_cputime_adjusted+0x59/0x70

Dave, could you test attached patch and check if make warnings gone.
Patch is not right fix, but if it prevent the warnings, this will
give clue where the problem can be.

Stanislaw
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index e93cca9..057faa8 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -313,7 +313,7 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
 		task_cputime(t, &utime, &stime);
 		times->utime += utime;
 		times->stime += stime;
-		times->sum_exec_runtime += task_sched_runtime(t);
+		times->sum_exec_runtime += t->se.sum_exec_runtime;
 	} while_each_thread(tsk, t);
 out:
 	rcu_read_unlock();