fork: call complete_vfork_done() after clearing child_tid and flushing rss-counters

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

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 017fb23d5983..2254fbf23567 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -787,9 +787,6 @@ 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
@@ -810,6 +807,13 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
                 }
                 tsk->clear_child_tid = NULL;
         }
+
+        /*
+         * 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);
 }
 
 /*