linux-kernel - [PATCH v3 1/3] posix_timers: do not account group_exec

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Date:	Mon, 29 Apr 2013 14:04:09 -0400
From:	Olivier Langlois <olivier@...vierlanglois.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, schwidefsky@...ibm.com,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 1/3] posix_timers: do not account group_exec_runtime for
 dying autoreaped tasks



Forbids the cputimer to drift ahead of its process clock by
blocking its update when a tick occurs while a autoreaping task
is currently in do_exit() between the call to release_task() and
its final call to schedule().

Any task stats update after having called release_task() will
be lost because they are added to the global process stats located
in the signal struct from release_task().

Signed-off-by: Olivier Langlois <olivier@...llion01.com>
---
 kernel/sched/fair.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7a33e59..52d7b10 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -708,7 +708,15 @@ static void update_curr(struct cfs_rq *cfs_rq)
 
                trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
                cpuacct_charge(curtask, delta_exec);
-               account_group_exec_runtime(curtask, delta_exec);
+               /*
+                * Do not update the cputimer if the task is already released by
+                * release_task().
+                *
+                * it would preferable to defer the autoreap release_task
+                * after the last context switch but harder to do.
+                */
+               if (likely(curtask->sighand))
+                       account_group_exec_runtime(curtask, delta_exec);
        }
 
        account_cfs_rq_runtime(cfs_rq, delta_exec);
-- 
1.8.2.1


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