Merge branch 'work.dcache2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull dcache and mountpoint updates from Al Viro:
 "Saner handling of refcounts to mountpoints.

  Transfer the counting reference from struct mount ->mnt_mountpoint
  over to struct mountpoint ->m_dentry. That allows us to get rid of the
  convoluted games with ordering of mount shutdowns.

  The cost is in teaching shrink_dcache_{parent,for_umount} to cope with
  mixed-filesystem shrink lists, which we'll also need for the Slab
  Movable Objects patchset"

* 'work.dcache2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  switch the remnants of releasing the mountpoint away from fs_pin
  get rid of detach_mnt()
  make struct mountpoint bear the dentry reference to mountpoint, not struct mount
  Teach shrink_dcache_parent() to cope with mixed-filesystem shrink lists
  fs/namespace.c: shift put_mountpoint() to callers of unhash_mnt()
  __detach_mounts(): lookup_mountpoint() can't return ERR_PTR() anymore
  nfs: dget_parent() never returns NULL
  ceph: don't open-code the check for dead lockref

8 files changed, 172 insertions, 116 deletions

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index aab29f48c62d..4ca0b8ff9a72 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -1267,7 +1267,7 @@ __dentry_leases_walk(struct ceph_mds_client *mdsc,
                 if (!spin_trylock(&dentry->d_lock))
                         continue;
 
-                if (dentry->d_lockref.count < 0) {
+                if (__lockref_is_dead(&dentry->d_lockref)) {
                         list_del_init(&di->lease_list);
                         goto next;
                 }
diff --git a/fs/dcache.c b/fs/dcache.c
index f41121e5d1ec..e88cf0554e65 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -861,6 +861,32 @@ void dput(struct dentry *dentry)
 }
 EXPORT_SYMBOL(dput);
 
+static void __dput_to_list(struct dentry *dentry, struct list_head *list)
+__must_hold(&dentry->d_lock)
+{
+        if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+                /* let the owner of the list it's on deal with it */
+                --dentry->d_lockref.count;
+        } else {
+                if (dentry->d_flags & DCACHE_LRU_LIST)
+                        d_lru_del(dentry);
+                if (!--dentry->d_lockref.count)
+                        d_shrink_add(dentry, list);
+        }
+}
+
+void dput_to_list(struct dentry *dentry, struct list_head *list)
+{
+        rcu_read_lock();
+        if (likely(fast_dput(dentry))) {
+                rcu_read_unlock();
+                return;
+        }
+        rcu_read_unlock();
+        if (!retain_dentry(dentry))
+                __dput_to_list(dentry, list);
+        spin_unlock(&dentry->d_lock);
+}
 
 /* This must be called with d_lock held */
 static inline void __dget_dlock(struct dentry *dentry)
@@ -1067,7 +1093,7 @@ out:
         return false;
 }
 
-static void shrink_dentry_list(struct list_head *list)
+void shrink_dentry_list(struct list_head *list)
 {
         while (!list_empty(list)) {
                 struct dentry *dentry, *parent;
@@ -1089,18 +1115,9 @@ static void shrink_dentry_list(struct list_head *list)
                 rcu_read_unlock();
                 d_shrink_del(dentry);
                 parent = dentry->d_parent;
+                if (parent != dentry)
+                        __dput_to_list(parent, list);
                 __dentry_kill(dentry);
-                if (parent == dentry)
-                        continue;
-                /*
-                 * We need to prune ancestors too. This is necessary to prevent
-                 * quadratic behavior of shrink_dcache_parent(), but is also
-                 * expected to be beneficial in reducing dentry cache
-                 * fragmentation.
-                 */
-                dentry = parent;
-                while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
-                        dentry = dentry_kill(dentry);
         }
 }
 
@@ -1445,8 +1462,11 @@ out:
 
 struct select_data {
         struct dentry *start;
+        union {
+                long found;
+                struct dentry *victim;
+        };
         struct list_head dispose;
-        int found;
 };
 
 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
@@ -1478,6 +1498,37 @@ out:
         return ret;
 }
 
+static enum d_walk_ret select_collect2(void *_data, struct dentry *dentry)
+{
+        struct select_data *data = _data;
+        enum d_walk_ret ret = D_WALK_CONTINUE;
+
+        if (data->start == dentry)
+                goto out;
+
+        if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+                if (!dentry->d_lockref.count) {
+                        rcu_read_lock();
+                        data->victim = dentry;
+                        return D_WALK_QUIT;
+                }
+        } else {
+                if (dentry->d_flags & DCACHE_LRU_LIST)
+                        d_lru_del(dentry);
+                if (!dentry->d_lockref.count)
+                        d_shrink_add(dentry, &data->dispose);
+        }
+        /*
+         * We can return to the caller if we have found some (this
+         * ensures forward progress). We'll be coming back to find
+         * the rest.
+         */
+        if (!list_empty(&data->dispose))
+                ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
+out:
+        return ret;
+}
+
 /**
  * shrink_dcache_parent - prune dcache
  * @parent: parent of entries to prune
@@ -1487,12 +1538,9 @@ out:
 void shrink_dcache_parent(struct dentry *parent)
 {
         for (;;) {
-                struct select_data data;
+                struct select_data data = {.start = parent};
 
                 INIT_LIST_HEAD(&data.dispose);
-                data.start = parent;
-                data.found = 0;
-
                 d_walk(parent, &data, select_collect);
 
                 if (!list_empty(&data.dispose)) {
@@ -1503,6 +1551,24 @@ void shrink_dcache_parent(struct dentry *parent)
                 cond_resched();
                 if (!data.found)
                         break;
+                data.victim = NULL;
+                d_walk(parent, &data, select_collect2);
+                if (data.victim) {
+                        struct dentry *parent;
+                        spin_lock(&data.victim->d_lock);
+                        if (!shrink_lock_dentry(data.victim)) {
+                                spin_unlock(&data.victim->d_lock);
+                                rcu_read_unlock();
+                        } else {
+                                rcu_read_unlock();
+                                parent = data.victim->d_parent;
+                                if (parent != data.victim)
+                                        __dput_to_list(parent, &data.dispose);
+                                __dentry_kill(data.victim);
+                        }
+                }
+                if (!list_empty(&data.dispose))
+                        shrink_dentry_list(&data.dispose);
         }
 }
 EXPORT_SYMBOL(shrink_dcache_parent);
diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index a6497cf8ae53..47ef3c71ce90 100644
--- a/fs/fs_pin.c
+++ b/fs/fs_pin.c
@@ -19,20 +19,14 @@ void pin_remove(struct fs_pin *pin)
         spin_unlock_irq(&pin->wait.lock);
 }
 
-void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
+void pin_insert(struct fs_pin *pin, struct vfsmount *m)
 {
         spin_lock(&pin_lock);
-        if (p)
-                hlist_add_head(&pin->s_list, p);
+        hlist_add_head(&pin->s_list, &m->mnt_sb->s_pins);
         hlist_add_head(&pin->m_list, &real_mount(m)->mnt_pins);
         spin_unlock(&pin_lock);
 }
 
-void pin_insert(struct fs_pin *pin, struct vfsmount *m)
-{
-        pin_insert_group(pin, m, &m->mnt_sb->s_pins);
-}
-
 void pin_kill(struct fs_pin *p)
 {
         wait_queue_entry_t wait;
diff --git a/fs/internal.h b/fs/internal.h
index ff5173212803..315fcd8d237c 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -157,6 +157,8 @@ extern long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc);
 extern struct dentry *d_alloc_cursor(struct dentry *);
 extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
 extern char *simple_dname(struct dentry *, char *, int);
+extern void dput_to_list(struct dentry *, struct list_head *);
+extern void shrink_dentry_list(struct list_head *);
 
 /*
  * read_write.c
diff --git a/fs/mount.h b/fs/mount.h
index 6250de544760..711a4093e475 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -58,7 +58,10 @@ struct mount {
         struct mount *mnt_master;       /* slave is on master->mnt_slave_list */
         struct mnt_namespace *mnt_ns;   /* containing namespace */
         struct mountpoint *mnt_mp;      /* where is it mounted */
-        struct hlist_node mnt_mp_list;  /* list mounts with the same mountpoint */
+        union {
+                struct hlist_node mnt_mp_list;  /* list mounts with the same mountpoint */
+                struct hlist_node mnt_umount;
+        };
         struct list_head mnt_umounting; /* list entry for umount propagation */
 #ifdef CONFIG_FSNOTIFY
         struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks;
@@ -68,8 +71,7 @@ struct mount {
         int mnt_group_id;               /* peer group identifier */
         int mnt_expiry_mark;            /* true if marked for expiry */
         struct hlist_head mnt_pins;
-        struct fs_pin mnt_umount;
-        struct dentry *mnt_ex_mountpoint;
+        struct hlist_head mnt_stuck_children;
 } __randomize_layout;
 
 #define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
diff --git a/fs/namespace.c b/fs/namespace.c
index f0d664adb9ba..6464ea4acba9 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -70,6 +70,8 @@ static struct hlist_head *mount_hashtable __read_mostly;
 static struct hlist_head *mountpoint_hashtable __read_mostly;
 static struct kmem_cache *mnt_cache __read_mostly;
 static DECLARE_RWSEM(namespace_sem);
+static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
+static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
 
 /* /sys/fs */
 struct kobject *fs_kobj;
@@ -170,14 +172,6 @@ unsigned int mnt_get_count(struct mount *mnt)
 #endif
 }
 
-static void drop_mountpoint(struct fs_pin *p)
-{
-        struct mount *m = container_of(p, struct mount, mnt_umount);
-        dput(m->mnt_ex_mountpoint);
-        pin_remove(p);
-        mntput(&m->mnt);
-}
-
 static struct mount *alloc_vfsmnt(const char *name)
 {
         struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -215,7 +209,7 @@ static struct mount *alloc_vfsmnt(const char *name)
                 INIT_LIST_HEAD(&mnt->mnt_slave);
                 INIT_HLIST_NODE(&mnt->mnt_mp_list);
                 INIT_LIST_HEAD(&mnt->mnt_umounting);
-                init_fs_pin(&mnt->mnt_umount, drop_mountpoint);
+                INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
         }
         return mnt;
 
@@ -740,7 +734,7 @@ mountpoint:
 
         /* Add the new mountpoint to the hash table */
         read_seqlock_excl(&mount_lock);
-        new->m_dentry = dentry;
+        new->m_dentry = dget(dentry);
         new->m_count = 1;
         hlist_add_head(&new->m_hash, mp_hash(dentry));
         INIT_HLIST_HEAD(&new->m_list);
@@ -753,7 +747,11 @@ done:
         return mp;
 }
 
-static void put_mountpoint(struct mountpoint *mp)
+/*
+ * vfsmount lock must be held.  Additionally, the caller is responsible
+ * for serializing calls for given disposal list.
+ */
+static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
 {
         if (!--mp->m_count) {
                 struct dentry *dentry = mp->m_dentry;
@@ -761,11 +759,18 @@ static void put_mountpoint(struct mountpoint *mp)
                 spin_lock(&dentry->d_lock);
                 dentry->d_flags &= ~DCACHE_MOUNTED;
                 spin_unlock(&dentry->d_lock);
+                dput_to_list(dentry, list);
                 hlist_del(&mp->m_hash);
                 kfree(mp);
         }
 }
 
+/* called with namespace_lock and vfsmount lock */
+static void put_mountpoint(struct mountpoint *mp)
+{
+        __put_mountpoint(mp, &ex_mountpoints);
+}
+
 static inline int check_mnt(struct mount *mnt)
 {
         return mnt->mnt_ns == current->nsproxy->mnt_ns;
@@ -796,25 +801,17 @@ static void __touch_mnt_namespace(struct mnt_namespace *ns)
 /*
  * vfsmount lock must be held for write
  */
-static void unhash_mnt(struct mount *mnt)
+static struct mountpoint *unhash_mnt(struct mount *mnt)
 {
+        struct mountpoint *mp;
         mnt->mnt_parent = mnt;
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         list_del_init(&mnt->mnt_child);
         hlist_del_init_rcu(&mnt->mnt_hash);
         hlist_del_init(&mnt->mnt_mp_list);
-        put_mountpoint(mnt->mnt_mp);
+        mp = mnt->mnt_mp;
         mnt->mnt_mp = NULL;
-}
-
-/*
- * vfsmount lock must be held for write
- */
-static void detach_mnt(struct mount *mnt, struct path *old_path)
-{
-        old_path->dentry = mnt->mnt_mountpoint;
-        old_path->mnt = &mnt->mnt_parent->mnt;
-        unhash_mnt(mnt);
+        return mp;
 }
 
 /*
@@ -822,9 +819,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
  */
 static void umount_mnt(struct mount *mnt)
 {
-        /* old mountpoint will be dropped when we can do that */
-        mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
-        unhash_mnt(mnt);
+        put_mountpoint(unhash_mnt(mnt));
 }
 
 /*
@@ -836,7 +831,7 @@ void mnt_set_mountpoint(struct mount *mnt,
 {
         mp->m_count++;
         mnt_add_count(mnt, 1);  /* essentially, that's mntget */
-        child_mnt->mnt_mountpoint = dget(mp->m_dentry);
+        child_mnt->mnt_mountpoint = mp->m_dentry;
         child_mnt->mnt_parent = mnt;
         child_mnt->mnt_mp = mp;
         hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
@@ -863,7 +858,6 @@ static void attach_mnt(struct mount *mnt,
 void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
 {
         struct mountpoint *old_mp = mnt->mnt_mp;
-        struct dentry *old_mountpoint = mnt->mnt_mountpoint;
         struct mount *old_parent = mnt->mnt_parent;
 
         list_del_init(&mnt->mnt_child);
@@ -873,22 +867,6 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m
         attach_mnt(mnt, parent, mp);
 
         put_mountpoint(old_mp);
-
-        /*
-         * Safely avoid even the suggestion this code might sleep or
-         * lock the mount hash by taking advantage of the knowledge that
-         * mnt_change_mountpoint will not release the final reference
-         * to a mountpoint.
-         *
-         * During mounting, the mount passed in as the parent mount will
-         * continue to use the old mountpoint and during unmounting, the
-         * old mountpoint will continue to exist until namespace_unlock,
-         * which happens well after mnt_change_mountpoint.
-         */
-        spin_lock(&old_mountpoint->d_lock);
-        old_mountpoint->d_lockref.count--;
-        spin_unlock(&old_mountpoint->d_lock);
-
         mnt_add_count(old_parent, -1);
 }
 
@@ -1103,19 +1081,22 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 
 static void cleanup_mnt(struct mount *mnt)
 {
+        struct hlist_node *p;
+        struct mount *m;
         /*
-         * This probably indicates that somebody messed
-         * up a mnt_want/drop_write() pair.  If this
-         * happens, the filesystem was probably unable
-         * to make r/w->r/o transitions.
-         */
-        /*
+         * The warning here probably indicates that somebody messed
+         * up a mnt_want/drop_write() pair.  If this happens, the
+         * filesystem was probably unable to make r/w->r/o transitions.
          * The locking used to deal with mnt_count decrement provides barriers,
          * so mnt_get_writers() below is safe.
          */
         WARN_ON(mnt_get_writers(mnt));
         if (unlikely(mnt->mnt_pins.first))
                 mnt_pin_kill(mnt);
+        hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
+                hlist_del(&m->mnt_umount);
+                mntput(&m->mnt);
+        }
         fsnotify_vfsmount_delete(&mnt->mnt);
         dput(mnt->mnt.mnt_root);
         deactivate_super(mnt->mnt.mnt_sb);
@@ -1141,6 +1122,8 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
 
 static void mntput_no_expire(struct mount *mnt)
 {
+        LIST_HEAD(list);
+
         rcu_read_lock();
         if (likely(READ_ONCE(mnt->mnt_ns))) {
                 /*
@@ -1181,10 +1164,12 @@ static void mntput_no_expire(struct mount *mnt)
         if (unlikely(!list_empty(&mnt->mnt_mounts))) {
                 struct mount *p, *tmp;
                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
-                        umount_mnt(p);
+                        __put_mountpoint(unhash_mnt(p), &list);
+                        hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
                 }
         }
         unlock_mount_hash();
+        shrink_dentry_list(&list);
 
         if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
                 struct task_struct *task = current;
@@ -1370,22 +1355,29 @@ int may_umount(struct vfsmount *mnt)
 
 EXPORT_SYMBOL(may_umount);
 
-static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
-
 static void namespace_unlock(void)
 {
         struct hlist_head head;
+        struct hlist_node *p;
+        struct mount *m;
+        LIST_HEAD(list);
 
         hlist_move_list(&unmounted, &head);
+        list_splice_init(&ex_mountpoints, &list);
 
         up_write(&namespace_sem);
 
+        shrink_dentry_list(&list);
+
         if (likely(hlist_empty(&head)))
                 return;
 
         synchronize_rcu_expedited();
 
-        group_pin_kill(&head);
+        hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
+                hlist_del(&m->mnt_umount);
+                mntput(&m->mnt);
+        }
 }
 
 static inline void namespace_lock(void)
@@ -1472,8 +1464,6 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 
                 disconnect = disconnect_mount(p, how);
 
-                pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
-                                 disconnect ? &unmounted : NULL);
                 if (mnt_has_parent(p)) {
                         mnt_add_count(p->mnt_parent, -1);
                         if (!disconnect) {
@@ -1481,6 +1471,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
                                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
                         } else {
                                 umount_mnt(p);
+                                hlist_add_head(&p->mnt_umount, &unmounted);
                         }
                 }
                 change_mnt_propagation(p, MS_PRIVATE);
@@ -1626,15 +1617,15 @@ void __detach_mounts(struct dentry *dentry)
         namespace_lock();
         lock_mount_hash();
         mp = lookup_mountpoint(dentry);
-        if (IS_ERR_OR_NULL(mp))
+        if (!mp)
                 goto out_unlock;
 
         event++;
         while (!hlist_empty(&mp->m_list)) {
                 mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
                 if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
-                        hlist_add_head(&mnt->mnt_umount.s_list, &unmounted);
                         umount_mnt(mnt);
+                        hlist_add_head(&mnt->mnt_umount, &unmounted);
                 }
                 else umount_tree(mnt, UMOUNT_CONNECTED);
         }
@@ -2046,7 +2037,7 @@ int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
 static int attach_recursive_mnt(struct mount *source_mnt,
                         struct mount *dest_mnt,
                         struct mountpoint *dest_mp,
-                        struct path *parent_path)
+                        bool moving)
 {
         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
         HLIST_HEAD(tree_list);
@@ -2064,7 +2055,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
                 return PTR_ERR(smp);
 
         /* Is there space to add these mounts to the mount namespace? */
-        if (!parent_path) {
+        if (!moving) {
                 err = count_mounts(ns, source_mnt);
                 if (err)
                         goto out;
@@ -2083,8 +2074,8 @@ static int attach_recursive_mnt(struct mount *source_mnt,
         } else {
                 lock_mount_hash();
         }
-        if (parent_path) {
-                detach_mnt(source_mnt, parent_path);
+        if (moving) {
+                unhash_mnt(source_mnt);
                 attach_mnt(source_mnt, dest_mnt, dest_mp);
                 touch_mnt_namespace(source_mnt->mnt_ns);
         } else {
@@ -2182,7 +2173,7 @@ static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
               d_is_dir(mnt->mnt.mnt_root))
                 return -ENOTDIR;
 
-        return attach_recursive_mnt(mnt, p, mp, NULL);
+        return attach_recursive_mnt(mnt, p, mp, false);
 }
 
 /*
@@ -2575,11 +2566,11 @@ out:
 
 static int do_move_mount(struct path *old_path, struct path *new_path)
 {
-        struct path parent_path = {.mnt = NULL, .dentry = NULL};
         struct mnt_namespace *ns;
         struct mount *p;
         struct mount *old;
-        struct mountpoint *mp;
+        struct mount *parent;
+        struct mountpoint *mp, *old_mp;
         int err;
         bool attached;
 
@@ -2589,7 +2580,9 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
 
         old = real_mount(old_path->mnt);
         p = real_mount(new_path->mnt);
+        parent = old->mnt_parent;
         attached = mnt_has_parent(old);
+        old_mp = old->mnt_mp;
         ns = old->mnt_ns;
 
         err = -EINVAL;
@@ -2617,7 +2610,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
         /*
          * Don't move a mount residing in a shared parent.
          */
-        if (attached && IS_MNT_SHARED(old->mnt_parent))
+        if (attached && IS_MNT_SHARED(parent))
                 goto out;
         /*
          * Don't move a mount tree containing unbindable mounts to a destination
@@ -2633,18 +2626,21 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
                         goto out;
 
         err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,
-                                   attached ? &parent_path : NULL);
+                                   attached);
         if (err)
                 goto out;
 
         /* if the mount is moved, it should no longer be expire
          * automatically */
         list_del_init(&old->mnt_expire);
+        if (attached)
+                put_mountpoint(old_mp);
 out:
         unlock_mount(mp);
         if (!err) {
-                path_put(&parent_path);
-                if (!attached)
+                if (attached)
+                        mntput_no_expire(parent);
+                else
                         free_mnt_ns(ns);
         }
         return err;
@@ -3589,8 +3585,8 @@ EXPORT_SYMBOL(path_is_under);
 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                 const char __user *, put_old)
 {
-        struct path new, old, parent_path, root_parent, root;
-        struct mount *new_mnt, *root_mnt, *old_mnt;
+        struct path new, old, root;
+        struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
         struct mountpoint *old_mp, *root_mp;
         int error;
 
@@ -3619,9 +3615,11 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
         new_mnt = real_mount(new.mnt);
         root_mnt = real_mount(root.mnt);
         old_mnt = real_mount(old.mnt);
+        ex_parent = new_mnt->mnt_parent;
+        root_parent = root_mnt->mnt_parent;
         if (IS_MNT_SHARED(old_mnt) ||
-                IS_MNT_SHARED(new_mnt->mnt_parent) ||
-                IS_MNT_SHARED(root_mnt->mnt_parent))
+                IS_MNT_SHARED(ex_parent) ||
+                IS_MNT_SHARED(root_parent))
                 goto out4;
         if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
                 goto out4;
@@ -3638,7 +3636,6 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(root_mnt))
                 goto out4; /* not attached */
-        root_mp = root_mnt->mnt_mp;
         if (new.mnt->mnt_root != new.dentry)
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(new_mnt))
@@ -3649,10 +3646,9 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
         /* make certain new is below the root */
         if (!is_path_reachable(new_mnt, new.dentry, &root))
                 goto out4;
-        root_mp->m_count++; /* pin it so it won't go away */
         lock_mount_hash();
-        detach_mnt(new_mnt, &parent_path);
-        detach_mnt(root_mnt, &root_parent);
+        umount_mnt(new_mnt);
+        root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */
         if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
                 new_mnt->mnt.mnt_flags |= MNT_LOCKED;
                 root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
@@ -3660,7 +3656,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
         /* mount old root on put_old */
         attach_mnt(root_mnt, old_mnt, old_mp);
         /* mount new_root on / */
-        attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
+        attach_mnt(new_mnt, root_parent, root_mp);
+        mnt_add_count(root_parent, -1);
         touch_mnt_namespace(current->nsproxy->mnt_ns);
         /* A moved mount should not expire automatically */
         list_del_init(&new_mnt->mnt_expire);
@@ -3670,10 +3667,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
         error = 0;
 out4:
         unlock_mount(old_mp);
-        if (!error) {
-                path_put(&root_parent);
-                path_put(&parent_path);
-        }
+        if (!error)
+                mntput_no_expire(ex_parent);
 out3:
         path_put(&root);
 out2:
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 3683d2b1cc8e..628631e2e34f 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -457,10 +457,8 @@ int nfs_statfs(struct dentry *dentry, struct kstatfs *buf)
                 struct dentry *pd_dentry;
 
                 pd_dentry = dget_parent(dentry);
-                if (pd_dentry != NULL) {
-                        nfs_zap_caches(d_inode(pd_dentry));
-                        dput(pd_dentry);
-                }
+                nfs_zap_caches(d_inode(pd_dentry));
+                dput(pd_dentry);
         }
         nfs_free_fattr(res.fattr);
         if (error < 0)
diff --git a/include/linux/fs_pin.h b/include/linux/fs_pin.h
index 7cab74d66f85..bdd09fd2520c 100644
--- a/include/linux/fs_pin.h
+++ b/include/linux/fs_pin.h
@@ -20,6 +20,5 @@ static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *))
 }
 
 void pin_remove(struct fs_pin *);
-void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *);
 void pin_insert(struct fs_pin *, struct vfsmount *);
 void pin_kill(struct fs_pin *);