coredump_wait: don't call complete_vfork_done()

Now that CLONE_VFORK is killable, coredump_wait() no longer needs
complete_vfork_done().  zap_threads() should find and kill all tasks with
the same ->mm, this includes our parent if ->vfork_done is set.

mm_release() becomes the only caller, unexport complete_vfork_done().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1926,19 +1926,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 		core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 	up_write(&mm->mmap_sem);
 
-	if (unlikely(core_waiters < 0))
+	if (core_waiters > 0)
-		goto fail;
-
-	/*
-	 * Make sure nobody is waiting for us to release the VM,
-	 * otherwise we can deadlock when we wait on each other
-	 */
-	if (tsk->vfork_done)
-		complete_vfork_done(tsk);
-
-	if (core_waiters)
 		wait_for_completion(&core_state->startup);
-fail:
+
 	return core_waiters;
 }
 

include/linux/sched.h

@@ -2291,7 +2291,6 @@ extern int do_execve(const char *,
 		     const char __user * const __user *,
 		     const char __user * const __user *, struct pt_regs *);
 extern long do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int __user *, int __user *);
-extern void complete_vfork_done(struct task_struct *tsk);
 struct task_struct *fork_idle(int);
 
 extern void set_task_comm(struct task_struct *tsk, char *from);

kernel/fork.c

@@ -668,7 +668,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 	return mm;
 }
 
-void complete_vfork_done(struct task_struct *tsk)
+static void complete_vfork_done(struct task_struct *tsk)
 {
 	struct completion *vfork;