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)

3 files changed, 14 insertions, 69 deletions

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 78b519c..251ebe8 100644
--- a/fs/fs_struct.c
+++ b/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.
@@ -30,11 +18,11 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
 	write_seqcount_begin(&fs->seq);
 	old_root = fs->root;
 	fs->root = *path;
-	path_get_longterm(path);
+	path_get(path);
 	write_seqcount_end(&fs->seq);
 	spin_unlock(&fs->lock);
 	if (old_root.dentry)
-		path_put_longterm(&old_root);
+		path_put(&old_root);
 }
 
 /*
@@ -49,12 +37,12 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path)
 	write_seqcount_begin(&fs->seq);
 	old_pwd = fs->pwd;
 	fs->pwd = *path;
-	path_get_longterm(path);
+	path_get(path);
 	write_seqcount_end(&fs->seq);
 	spin_unlock(&fs->lock);
 
 	if (old_pwd.dentry)
-		path_put_longterm(&old_pwd);
+		path_put(&old_pwd);
 }
 
 void chroot_fs_refs(struct path *old_root, struct path *new_root)
@@ -72,13 +60,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
 			write_seqcount_begin(&fs->seq);
 			if (fs->root.dentry == old_root->dentry
 			    && fs->root.mnt == old_root->mnt) {
-				path_get_longterm(new_root);
+				path_get(new_root);
 				fs->root = *new_root;
 				count++;
 			}
 			if (fs->pwd.dentry == old_root->dentry
 			    && fs->pwd.mnt == old_root->mnt) {
-				path_get_longterm(new_root);
+				path_get(new_root);
 				fs->pwd = *new_root;
 				count++;
 			}
@@ -89,13 +77,13 @@ 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);
 }
 
@@ -131,9 +119,9 @@ 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;
diff --git a/fs/internal.h b/fs/internal.h
index 552ca03..4e194bb 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -72,9 +72,6 @@ extern void umount_tree(struct vfsmount *, int, struct list_head *);
 extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
 extern int finish_automount(struct vfsmount *, struct path *);
 
-extern void mnt_make_longterm(struct vfsmount *);
-extern void mnt_make_shortterm(struct vfsmount *);
-
 extern void __init mnt_init(void);
 
 extern struct lglock vfsmount_lock;
diff --git a/fs/namespace.c b/fs/namespace.c
index 33ad187..0fd3f8a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -609,21 +609,6 @@ static void attach_mnt(struct vfsmount *mnt, struct path *path)
 	list_add_tail(&mnt->mnt_child, &path->mnt->mnt_mounts);
 }
 
-static inline void __mnt_make_longterm(struct vfsmount *mnt)
-{
-#ifdef CONFIG_SMP
-	atomic_inc(&mnt->mnt_longterm);
-#endif
-}
-
-/* needs vfsmount lock for write */
-static inline void __mnt_make_shortterm(struct vfsmount *mnt)
-{
-#ifdef CONFIG_SMP
-	atomic_dec(&mnt->mnt_longterm);
-#endif
-}
-
 /*
  * vfsmount lock must be held for write
  */
@@ -637,10 +622,8 @@ static void commit_tree(struct vfsmount *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);
 
@@ -785,7 +768,8 @@ static void mntput_no_expire(struct vfsmount *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_dec_count(mnt);
 		br_read_unlock(&vfsmount_lock);
 		return;
@@ -1250,8 +1234,6 @@ void umount_tree(struct vfsmount *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 (p->mnt_parent != p) {
@@ -2375,22 +2357,6 @@ static struct mnt_namespace *alloc_mnt_ns(void)
 	return new_ns;
 }
 
-void mnt_make_longterm(struct vfsmount *mnt)
-{
-	__mnt_make_longterm(mnt);
-}
-
-void mnt_make_shortterm(struct vfsmount *mnt)
-{
-#ifdef CONFIG_SMP
-	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.
@@ -2428,18 +2394,13 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
 	q = new_ns->root;
 	while (p) {
 		q->mnt_ns = new_ns;
-		__mnt_make_longterm(q);
 		if (fs) {
 			if (p == fs->root.mnt) {
 				fs->root.mnt = mntget(q);
-				__mnt_make_longterm(q);
-				mnt_make_shortterm(p);
 				rootmnt = p;
 			}
 			if (p == fs->pwd.mnt) {
 				fs->pwd.mnt = mntget(q);
-				__mnt_make_longterm(q);
-				mnt_make_shortterm(p);
 				pwdmnt = p;
 			}
 		}
@@ -2484,7 +2445,6 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
 	new_ns = alloc_mnt_ns();
 	if (!IS_ERR(new_ns)) {
 		mnt->mnt_ns = new_ns;
-		__mnt_make_longterm(mnt);
 		new_ns->root = mnt;
 		list_add(&new_ns->list, &new_ns->root->mnt_list);
 	}