linux-kernel - [PATCH 4/5] exit: release_task: fix the comment about group leader accounting

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Message-ID: <20141114013823.GA5129@redhat.com>
Date:	Fri, 14 Nov 2014 02:38:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Aaron Tomlin <atomlin@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rik van Riel <riel@...hat.com>,
	Sterling Alexander <stalexan@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/5] exit: release_task: fix the comment about group leader
	accounting

Contrary to what the comment in __exit_signal() says we do account the
group leader. Fix this and explain why.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/exit.c |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index e0914eb..f773863 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -118,13 +118,10 @@ static void __exit_signal(struct task_struct *tsk)
 	}
 
 	/*
-	 * Accumulate here the counters for all threads but the group leader
-	 * as they die, so they can be added into the process-wide totals
-	 * when those are taken.  The group leader stays around as a zombie as
-	 * long as there are other threads.  When it gets reaped, the exit.c
-	 * code will add its counts into these totals.  We won't ever get here
-	 * for the group leader, since it will have been the last reference on
-	 * the signal_struct.
+	 * Accumulate here the counters for all threads as they die. We could
+	 * skip the group leader because it is the last user of signal_struct,
+	 * but we want to avoid the race with thread_group_cputime() which can
+	 * see the empty ->thread_head list.
 	 */
 	task_cputime(tsk, &utime, &stime);
 	write_seqlock(&sig->stats_lock);
-- 
1.5.5.1

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