1 files changed, 34 insertions, 26 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 5c372c954f3b..be8aa5b98666 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -606,6 +606,11 @@ static void __mmdrop(struct mm_struct *mm)
 
 void mmdrop(struct mm_struct *mm)
 {
+	/*
+	 * The implicit full barrier implied by atomic_dec_and_test() is
+	 * required by the membarrier system call before returning to
+	 * user-space, after storing to rq->curr.
+	 */
 	if (unlikely(atomic_dec_and_test(&mm->mm_count)))
 		__mmdrop(mm);
 }
@@ -1587,6 +1592,10 @@ static __latent_entropy struct task_struct *copy_process(
 	int retval;
 	struct task_struct *p;
 
+	/*
+	 * Don't allow sharing the root directory with processes in a different
+	 * namespace
+	 */
 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
 		return ERR_PTR(-EINVAL);
 
@@ -2062,6 +2071,8 @@ long _do_fork(unsigned long clone_flags,
 	      int __user *child_tidptr,
 	      unsigned long tls)
 {
+	struct completion vfork;
+	struct pid *pid;
 	struct task_struct *p;
 	int trace = 0;
 	long nr;
@@ -2087,43 +2098,40 @@ long _do_fork(unsigned long clone_flags,
 	p = copy_process(clone_flags, stack_start, stack_size,
 			 child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
 	add_latent_entropy();
+
+	if (IS_ERR(p))
+		return PTR_ERR(p);
+
 	/*
 	 * Do this prior waking up the new thread - the thread pointer
 	 * might get invalid after that point, if the thread exits quickly.
 	 */
-	if (!IS_ERR(p)) {
-		struct completion vfork;
-		struct pid *pid;
-
-		trace_sched_process_fork(current, p);
+	trace_sched_process_fork(current, p);
 
-		pid = get_task_pid(p, PIDTYPE_PID);
-		nr = pid_vnr(pid);
+	pid = get_task_pid(p, PIDTYPE_PID);
+	nr = pid_vnr(pid);
 
-		if (clone_flags & CLONE_PARENT_SETTID)
-			put_user(nr, parent_tidptr);
+	if (clone_flags & CLONE_PARENT_SETTID)
+		put_user(nr, parent_tidptr);
 
-		if (clone_flags & CLONE_VFORK) {
-			p->vfork_done = &vfork;
-			init_completion(&vfork);
-			get_task_struct(p);
-		}
-
-		wake_up_new_task(p);
+	if (clone_flags & CLONE_VFORK) {
+		p->vfork_done = &vfork;
+		init_completion(&vfork);
+		get_task_struct(p);
+	}
 
-		/* forking complete and child started to run, tell ptracer */
-		if (unlikely(trace))
-			ptrace_event_pid(trace, pid);
+	wake_up_new_task(p);
 
-		if (clone_flags & CLONE_VFORK) {
-			if (!wait_for_vfork_done(p, &vfork))
-				ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
-		}
+	/* forking complete and child started to run, tell ptracer */
+	if (unlikely(trace))
+		ptrace_event_pid(trace, pid);
 
-		put_pid(pid);
-	} else {
-		nr = PTR_ERR(p);
+	if (clone_flags & CLONE_VFORK) {
+		if (!wait_for_vfork_done(p, &vfork))
+			ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
 	}
+
+	put_pid(pid);
 	return nr;
 }