linux-kernel - [sched next] overflowed cpu time for kernel threads in /proc/PID/stat

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Date:	Tue, 20 Aug 2013 14:14:26 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Ingo Molnar <mingo@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: [sched next] overflowed cpu time for kernel threads in /proc/PID/stat

Hello,
3.11.0-rc6-next-20130820

at some point an overflowed cpu time is reported in /proc/PID/stat

cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 0 406 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 0 406 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 0 407 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 0 407 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 1844674407370 477 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
						^^^^^^^^^
cat /proc/10/stat
10 (rcu_preempt) S 2 0 0 0 -1 2129984 0 0 0 0 1844674407370 597 0 0 20 0 1 0 10 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 18446744073709551615 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0

(seems there are several more -1UL in output)


oddly enough, I see this happening only for RCU

 ps aux | grep rcu
 root         8  0.0  0.0      0     0 ?        S    12:42   0:00  [rcuc/0]
 root         9  0.0  0.0      0     0 ?        S    12:42   0:00  [rcub/0]
 root        10 62422329  0.0  0     0 ?        R    12:42 21114581:37  [rcu_preempt]
 root        11  0.1  0.0      0     0 ?        S    12:42   0:02  [rcuop/0]
 root        12 62422329  0.0  0     0 ?        S    12:42 21114581:35  [rcuop/1]

	-ss
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