1 files changed, 34 insertions, 5 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index e6c234b1a645..f7e28f8ea04d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -678,7 +678,7 @@ out:
  *
  * lookup_mnt takes a reference to the found vfsmount.
  */
-struct vfsmount *lookup_mnt(struct path *path)
+struct vfsmount *lookup_mnt(const struct path *path)
 {
 	struct mount *child_mnt;
 	struct vfsmount *m;
@@ -1159,7 +1159,36 @@ struct vfsmount *mntget(struct vfsmount *mnt)
 }
 EXPORT_SYMBOL(mntget);
 
-struct vfsmount *mnt_clone_internal(struct path *path)
+/* path_is_mountpoint() - Check if path is a mount in the current
+ *                          namespace.
+ *
+ *  d_mountpoint() can only be used reliably to establish if a dentry is
+ *  not mounted in any namespace and that common case is handled inline.
+ *  d_mountpoint() isn't aware of the possibility there may be multiple
+ *  mounts using a given dentry in a different namespace. This function
+ *  checks if the passed in path is a mountpoint rather than the dentry
+ *  alone.
+ */
+bool path_is_mountpoint(const struct path *path)
+{
+	unsigned seq;
+	bool res;
+
+	if (!d_mountpoint(path->dentry))
+		return false;
+
+	rcu_read_lock();
+	do {
+		seq = read_seqbegin(&mount_lock);
+		res = __path_is_mountpoint(path);
+	} while (read_seqretry(&mount_lock, seq));
+	rcu_read_unlock();
+
+	return res;
+}
+EXPORT_SYMBOL(path_is_mountpoint);
+
+struct vfsmount *mnt_clone_internal(const struct path *path)
 {
 	struct mount *p;
 	p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
@@ -1758,7 +1787,7 @@ out:
 
 /* Caller should check returned pointer for errors */
 
-struct vfsmount *collect_mounts(struct path *path)
+struct vfsmount *collect_mounts(const struct path *path)
 {
 	struct mount *tree;
 	namespace_lock();
@@ -1791,7 +1820,7 @@ void drop_collected_mounts(struct vfsmount *mnt)
  *
  * Release with mntput().
  */
-struct vfsmount *clone_private_mount(struct path *path)
+struct vfsmount *clone_private_mount(const struct path *path)
 {
 	struct mount *old_mnt = real_mount(path->mnt);
 	struct mount *new_mnt;
@@ -2997,7 +3026,7 @@ bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
 	return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
 }
 
-bool path_is_under(struct path *path1, struct path *path2)
+bool path_is_under(const struct path *path1, const struct path *path2)
 {
 	bool res;
 	read_seqlock_excl(&mount_lock);