Andrew Morton wrote:
On Thu, 12 Apr 2012 12:09:53 +0400
Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx> wrote:
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.
...
--- 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);
}
That does look a bit racy.
But are we really sure that the patch really does fix something?
Because it does increase vfork() latency a tiny bit.
I'm going to call this a patch against the fork subsystem, not the mm
subsystem.
I believe that this patch is unrelated to "mm: set task exit code
before complete_vfork_done()", yes?
Yes, unrelated.
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