get rid of ->mnt_longterm

it's enough to set ->mnt_ns of internal vfsmounts to something
distinct from all struct mnt_namespace out there; then we can
just use the check for ->mnt_ns != NULL in the fast path of
mntput_no_expire()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from commit f7a99c5b7c8bd3d3f533c8b38274e33f3da9096e)

fs/dcache.c

@@ -2558,7 +2558,7 @@ global_root:
 	if (!slash)
 		error = prepend(buffer, buflen, "/", 1);
 	if (!error)
-		error = real_mount(vfsmnt)->mnt_ns ? 1 : 2;
+		error = is_mounted(vfsmnt) ? 1 : 2;
 	goto out;
 }
 

fs/fs_struct.c

@@ -6,18 +6,6 @@
 #include <linux/fs_struct.h>
 #include "internal.h"
 
-static inline void path_get_longterm(struct path *path)
-{
-	path_get(path);
-	mnt_make_longterm(path->mnt);
-}
-
-static inline void path_put_longterm(struct path *path)
-{
-	mnt_make_shortterm(path->mnt);
-	path_put(path);
-}
-
 /*
  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
  * It can block.
@@ -26,7 +14,7 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
 {
 	struct path old_root;
 
-	path_get_longterm(path);
+	path_get(path);
 	spin_lock(&fs->lock);
 	write_seqcount_begin(&fs->seq);
 	old_root = fs->root;
@@ -34,7 +22,7 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
 	write_seqcount_end(&fs->seq);
 	spin_unlock(&fs->lock);
 	if (old_root.dentry)
-		path_put_longterm(&old_root);
+		path_put(&old_root);
 }
 
 /*
@@ -45,7 +33,7 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path)
 {
 	struct path old_pwd;
 
-	path_get_longterm(path);
+	path_get(path);
 	spin_lock(&fs->lock);
 	write_seqcount_begin(&fs->seq);
 	old_pwd = fs->pwd;
@@ -54,7 +42,7 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path)
 	spin_unlock(&fs->lock);
 
 	if (old_pwd.dentry)
-		path_put_longterm(&old_pwd);
+		path_put(&old_pwd);
 }
 
 static inline int replace_path(struct path *p, const struct path *old, const struct path *new)
@@ -84,7 +72,7 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
 			write_seqcount_end(&fs->seq);
 			while (hits--) {
 				count++;
-				path_get_longterm(new_root);
+				path_get(new_root);
 			}
 			spin_unlock(&fs->lock);
 		}
@@ -92,13 +80,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
 	} while_each_thread(g, p);
 	read_unlock(&tasklist_lock);
 	while (count--)
-		path_put_longterm(old_root);
+		path_put(old_root);
 }
 
 void free_fs_struct(struct fs_struct *fs)
 {
-	path_put_longterm(&fs->root);
-	path_put_longterm(&fs->pwd);
+	path_put(&fs->root);
+	path_put(&fs->pwd);
 	kmem_cache_free(fs_cachep, fs);
 }
 
@@ -132,9 +120,9 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
 
 		spin_lock(&old->lock);
 		fs->root = old->root;
-		path_get_longterm(&fs->root);
+		path_get(&fs->root);
 		fs->pwd = old->pwd;
-		path_get_longterm(&fs->pwd);
+		path_get(&fs->pwd);
 		spin_unlock(&old->lock);
 	}
 	return fs;

fs/internal.h

@@ -50,8 +50,6 @@ extern int copy_mount_string(const void __user *, char **);
 extern struct vfsmount *lookup_mnt(struct path *);
 extern int finish_automount(struct vfsmount *, struct path *);
 
-extern void mnt_make_longterm(struct vfsmount *);
-extern void mnt_make_shortterm(struct vfsmount *);
 extern int sb_prepare_remount_readonly(struct super_block *);
 
 extern void __init mnt_init(void);

fs/mount.h

@@ -22,7 +22,6 @@ struct mount {
 	struct vfsmount mnt;
 #ifdef CONFIG_SMP
 	struct mnt_pcp __percpu *mnt_pcp;
-	atomic_t mnt_longterm;		/* how many of the refs are longterm */
 #else
 	int mnt_count;
 	int mnt_writers;
@@ -49,6 +48,8 @@ struct mount {
 	int mnt_ghosts;
 };
 
+#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
+
 static inline struct mount *real_mount(struct vfsmount *mnt)
 {
 	return container_of(mnt, struct mount, mnt);
@@ -59,6 +60,12 @@ static inline int mnt_has_parent(struct mount *mnt)
 	return mnt != mnt->mnt_parent;
 }
 
+static inline int is_mounted(struct vfsmount *mnt)
+{
+	/* neither detached nor internal? */
+	return !IS_ERR_OR_NULL(real_mount(mnt));
+}
+
 extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
 
 static inline void get_mnt_ns(struct mnt_namespace *ns)

fs/namespace.c

@@ -621,21 +621,6 @@ static void attach_mnt(struct mount *mnt, struct path *path)
 	list_add_tail(&mnt->mnt_child, &real_mount(path->mnt)->mnt_mounts);
 }
 
-static inline void __mnt_make_longterm(struct mount *mnt)
-{
-#ifdef CONFIG_SMP
-	atomic_inc(&mnt->mnt_longterm);
-#endif
-}
-
-/* needs vfsmount lock for write */
-static inline void __mnt_make_shortterm(struct mount *mnt)
-{
-#ifdef CONFIG_SMP
-	atomic_dec(&mnt->mnt_longterm);
-#endif
-}
-
 /*
  * vfsmount lock must be held for write
  */
@@ -649,10 +634,8 @@ static void commit_tree(struct mount *mnt)
 	BUG_ON(parent == mnt);
 
 	list_add_tail(&head, &mnt->mnt_list);
-	list_for_each_entry(m, &head, mnt_list) {
+	list_for_each_entry(m, &head, mnt_list)
 		m->mnt_ns = n;
-		__mnt_make_longterm(m);
-	}
 
 	list_splice(&head, n->list.prev);
 
@@ -804,7 +787,8 @@ static void mntput_no_expire(struct mount *mnt)
 put_again:
 #ifdef CONFIG_SMP
 	br_read_lock(&vfsmount_lock);
-	if (likely(atomic_read(&mnt->mnt_longterm))) {
+	if (likely(mnt->mnt_ns)) {
+		/* shouldn't be the last one */
 		mnt_add_count(mnt, -1);
 		br_read_unlock(&vfsmount_lock);
 		return;
@@ -1074,8 +1058,6 @@ void umount_tree(struct mount *mnt, int propagate, struct list_head *kill)
 		list_del_init(&p->mnt_expire);
 		list_del_init(&p->mnt_list);
 		__touch_mnt_namespace(p->mnt_ns);
-		if (p->mnt_ns)
-			__mnt_make_shortterm(p);
 		p->mnt_ns = NULL;
 		list_del_init(&p->mnt_child);
 		if (mnt_has_parent(p)) {
@@ -2209,23 +2191,6 @@ static struct mnt_namespace *alloc_mnt_ns(void)
 	return new_ns;
 }
 
-void mnt_make_longterm(struct vfsmount *mnt)
-{
-	__mnt_make_longterm(real_mount(mnt));
-}
-
-void mnt_make_shortterm(struct vfsmount *m)
-{
-#ifdef CONFIG_SMP
-	struct mount *mnt = real_mount(m);
-	if (atomic_add_unless(&mnt->mnt_longterm, -1, 1))
-		return;
-	br_write_lock(&vfsmount_lock);
-	atomic_dec(&mnt->mnt_longterm);
-	br_write_unlock(&vfsmount_lock);
-#endif
-}
-
 /*
  * Allocate a new namespace structure and populate it with contents
  * copied from the namespace of the passed in task structure.
@@ -2265,18 +2230,13 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
 	q = new;
 	while (p) {
 		q->mnt_ns = new_ns;
-		__mnt_make_longterm(q);
 		if (fs) {
 			if (&p->mnt == fs->root.mnt) {
 				fs->root.mnt = mntget(&q->mnt);
-				__mnt_make_longterm(q);
-				mnt_make_shortterm(&p->mnt);
 				rootmnt = &p->mnt;
 			}
 			if (&p->mnt == fs->pwd.mnt) {
 				fs->pwd.mnt = mntget(&q->mnt);
-				__mnt_make_longterm(q);
-				mnt_make_shortterm(&p->mnt);
 				pwdmnt = &p->mnt;
 			}
 		}
@@ -2320,7 +2280,6 @@ static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
 	if (!IS_ERR(new_ns)) {
 		struct mount *mnt = real_mount(m);
 		mnt->mnt_ns = new_ns;
-		__mnt_make_longterm(mnt);
 		new_ns->root = mnt;
 		list_add(&new_ns->list, &mnt->mnt_list);
 	} else {
@@ -2615,7 +2574,7 @@ struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
 		 * it is a longterm mount, don't release mnt until
 		 * we unmount before file sys is unregistered
 		*/
-		mnt_make_longterm(mnt);
+		real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
 	}
 	return mnt;
 }
@@ -2625,7 +2584,9 @@ void kern_unmount(struct vfsmount *mnt)
 {
 	/* release long term mount so mount point can be released */
 	if (!IS_ERR_OR_NULL(mnt)) {
-		mnt_make_shortterm(mnt);
+		br_write_lock(&vfsmount_lock);
+		real_mount(mnt)->mnt_ns = NULL;
+		br_write_unlock(&vfsmount_lock);
 		mntput(mnt);
 	}
 }