linux-kernel - [PATCH 2/2] mm: call complete_vfork_done() after clearing child

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Date:	Thu, 12 Apr 2012 12:09:53 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: [PATCH 2/2] mm: call complete_vfork_done() after clearing child_tid
 and flushing rss-counters

Child should wake ups parent from vfork() only after finishing all operations with
shared mm. There is no sense to use CLONE_CHILD_CLEARTID together with CLONE_VFORK,
but it looks more accurate now.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc: Oleg Nesterov <oleg@...hat.com>
---
 kernel/fork.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 326bb5b..f10ac1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -728,9 +728,6 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 	/* Get rid of any cached register state */
 	deactivate_mm(tsk, mm);
 
-	if (tsk->vfork_done)
-		complete_vfork_done(tsk);
-
 	/*
 	 * If we're exiting normally, clear a user-space tid field if
 	 * requested.  We leave this alone when dying by signal, to leave
@@ -759,6 +756,13 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 	 */
 	if (mm)
 		sync_mm_rss(mm);
+
+	/*
+	 * All done, finally we can wake up parent and return this mm to him.
+	 * Also kthread_stop() uses this completion for synchronization.
+	 */
+	if (tsk->vfork_done)
+		complete_vfork_done(tsk);
 }
 
 /*

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