get rid of full-hash scan on detaching vfsmounts

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/mount.h b/fs/mount.h
index cd50079804003ece9325c5338089952f9fa0166b..64a858143ff923ab80499d5a865bde9de2257314 100644 (file)
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -18,6 +18,12 @@ struct mnt_pcp {
        int mnt_writers;
 };
 
+struct mountpoint {
+       struct list_head m_hash;
+       struct dentry *m_dentry;
+       int m_count;
+};
+
 struct mount {
        struct list_head mnt_hash;
        struct mount *mnt_parent;
@@ -40,6 +46,7 @@ struct mount {
        struct list_head mnt_slave;     /* slave list entry */
        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 */
 #ifdef CONFIG_FSNOTIFY
        struct hlist_head mnt_fsnotify_marks;
        __u32 mnt_fsnotify_mask;

diff --git a/fs/namespace.c b/fs/namespace.c
index 6c7d31eebba44c63f5dcf567f6b8a9e0b66e0047..d7bb5a55cf364a371c5e91846fa419f5ec15e803 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -36,6 +36,7 @@ static int mnt_id_start = 0;
 static int mnt_group_start = 1;
 
 static struct list_head *mount_hashtable __read_mostly;
+static struct list_head *mountpoint_hashtable __read_mostly;
 static struct kmem_cache *mnt_cache __read_mostly;
 static struct rw_semaphore namespace_sem;
 
@@ -605,6 +606,51 @@ struct vfsmount *lookup_mnt(struct path *path)
        }
 }
 
+static struct mountpoint *new_mountpoint(struct dentry *dentry)
+{
+       struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
+       struct mountpoint *mp;
+
+       list_for_each_entry(mp, chain, m_hash) {
+               if (mp->m_dentry == dentry) {
+                       /* might be worth a WARN_ON() */
+                       if (d_unlinked(dentry))
+                               return ERR_PTR(-ENOENT);
+                       mp->m_count++;
+                       return mp;
+               }
+       }
+
+       mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
+       if (!mp)
+               return ERR_PTR(-ENOMEM);
+
+       spin_lock(&dentry->d_lock);
+       if (d_unlinked(dentry)) {
+               spin_unlock(&dentry->d_lock);
+               kfree(mp);
+               return ERR_PTR(-ENOENT);
+       }
+       dentry->d_flags |= DCACHE_MOUNTED;
+       spin_unlock(&dentry->d_lock);
+       mp->m_dentry = dentry;
+       mp->m_count = 1;
+       list_add(&mp->m_hash, chain);
+       return mp;
+}
+
+static void put_mountpoint(struct mountpoint *mp)
+{
+       if (!--mp->m_count) {
+               struct dentry *dentry = mp->m_dentry;
+               spin_lock(&dentry->d_lock);
+               dentry->d_flags &= ~DCACHE_MOUNTED;
+               spin_unlock(&dentry->d_lock);
+               list_del(&mp->m_hash);
+               kfree(mp);
+       }
+}
+
 static inline int check_mnt(struct mount *mnt)
 {
        return mnt->mnt_ns == current->nsproxy->mnt_ns;
@@ -632,27 +678,6 @@ static void __touch_mnt_namespace(struct mnt_namespace *ns)
        }
 }
 
-/*
- * Clear dentry's mounted state if it has no remaining mounts.
- * vfsmount_lock must be held for write.
- */
-static void dentry_reset_mounted(struct dentry *dentry)
-{
-       unsigned u;
-
-       for (u = 0; u < HASH_SIZE; u++) {
-               struct mount *p;
-
-               list_for_each_entry(p, &mount_hashtable[u], mnt_hash) {
-                       if (p->mnt_mountpoint == dentry)
-                               return;
-               }
-       }
-       spin_lock(&dentry->d_lock);
-       dentry->d_flags &= ~DCACHE_MOUNTED;
-       spin_unlock(&dentry->d_lock);
-}
-
 /*
  * vfsmount lock must be held for write
  */
@@ -664,32 +689,35 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
        list_del_init(&mnt->mnt_child);
        list_del_init(&mnt->mnt_hash);
-       dentry_reset_mounted(old_path->dentry);
+       put_mountpoint(mnt->mnt_mp);
+       mnt->mnt_mp = NULL;
 }
 
 /*
  * vfsmount lock must be held for write
  */
-void mnt_set_mountpoint(struct mount *mnt, struct dentry *dentry,
+void mnt_set_mountpoint(struct mount *mnt,
+                       struct mountpoint *mp,
                        struct mount *child_mnt)
 {
+       mp->m_count++;
        mnt_add_count(mnt, 1);  /* essentially, that's mntget */
-       child_mnt->mnt_mountpoint = dget(dentry);
+       child_mnt->mnt_mountpoint = dget(mp->m_dentry);
        child_mnt->mnt_parent = mnt;
-       spin_lock(&dentry->d_lock);
-       dentry->d_flags |= DCACHE_MOUNTED;
-       spin_unlock(&dentry->d_lock);
+       child_mnt->mnt_mp = mp;
 }
 
 /*
  * vfsmount lock must be held for write
  */
-static void attach_mnt(struct mount *mnt, struct path *path)
+static void attach_mnt(struct mount *mnt,
+                       struct mount *parent,
+                       struct mountpoint *mp)
 {
-       mnt_set_mountpoint(real_mount(path->mnt), path->dentry, mnt);
+       mnt_set_mountpoint(parent, mp, mnt);
        list_add_tail(&mnt->mnt_hash, mount_hashtable +
-                       hash(path->mnt, path->dentry));
-       list_add_tail(&mnt->mnt_child, &real_mount(path->mnt)->mnt_mounts);
+                       hash(&parent->mnt, mp->m_dentry));
+       list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 }
 
 /*
@@ -1138,7 +1166,8 @@ void umount_tree(struct mount *mnt, int propagate, struct list_head *kill)
                list_del_init(&p->mnt_child);
                if (mnt_has_parent(p)) {
                        p->mnt_parent->mnt_ghosts++;
-                       dentry_reset_mounted(p->mnt_mountpoint);
+                       put_mountpoint(p->mnt_mp);
+                       p->mnt_mp = NULL;
                }
                change_mnt_propagation(p, MS_PRIVATE);
        }
@@ -1323,8 +1352,7 @@ static bool mnt_ns_loop(struct path *path)
 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
                                        int flag)
 {
-       struct mount *res, *p, *q, *r;
-       struct path path;
+       struct mount *res, *p, *q, *r, *parent;
 
        if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
                return ERR_PTR(-EINVAL);
@@ -1351,14 +1379,13 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
                                q = q->mnt_parent;
                        }
                        p = s;
-                       path.mnt = &q->mnt;
-                       path.dentry = p->mnt_mountpoint;
+                       parent = q;
                        q = clone_mnt(p, p->mnt.mnt_root, flag);
                        if (IS_ERR(q))
                                goto out;
                        br_write_lock(&vfsmount_lock);
                        list_add_tail(&q->mnt_list, &res->mnt_list);
-                       attach_mnt(q, &path);
+                       attach_mnt(q, parent, p->mnt_mp);
                        br_write_unlock(&vfsmount_lock);
                }
        }
@@ -1505,11 +1532,11 @@ static int invent_group_ids(struct mount *mnt, bool recurse)
  * in allocations.
  */
 static int attach_recursive_mnt(struct mount *source_mnt,
-                       struct path *path, struct path *parent_path)
+                       struct mount *dest_mnt,
+                       struct mountpoint *dest_mp,
+                       struct path *parent_path)
 {
        LIST_HEAD(tree_list);
-       struct mount *dest_mnt = real_mount(path->mnt);
-       struct dentry *dest_dentry = path->dentry;
        struct mount *child, *p;
        int err;
 
@@ -1518,7 +1545,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
                if (err)
                        goto out;
        }
-       err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list);
+       err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
        if (err)
                goto out_cleanup_ids;
 
@@ -1530,10 +1557,10 @@ static int attach_recursive_mnt(struct mount *source_mnt,
        }
        if (parent_path) {
                detach_mnt(source_mnt, parent_path);
-               attach_mnt(source_mnt, path);
+               attach_mnt(source_mnt, dest_mnt, dest_mp);
                touch_mnt_namespace(source_mnt->mnt_ns);
        } else {
-               mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
+               mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
                commit_tree(source_mnt);
        }
 
@@ -1552,46 +1579,53 @@ static int attach_recursive_mnt(struct mount *source_mnt,
        return err;
 }
 
-static int lock_mount(struct path *path)
+static struct mountpoint *lock_mount(struct path *path)
 {
        struct vfsmount *mnt;
+       struct dentry *dentry = path->dentry;
 retry:
-       mutex_lock(&path->dentry->d_inode->i_mutex);
-       if (unlikely(cant_mount(path->dentry))) {
-               mutex_unlock(&path->dentry->d_inode->i_mutex);
-               return -ENOENT;
+       mutex_lock(&dentry->d_inode->i_mutex);
+       if (unlikely(cant_mount(dentry))) {
+               mutex_unlock(&dentry->d_inode->i_mutex);
+               return ERR_PTR(-ENOENT);
        }
        down_write(&namespace_sem);
        mnt = lookup_mnt(path);
-       if (likely(!mnt))
-               return 0;
+       if (likely(!mnt)) {
+               struct mountpoint *mp = new_mountpoint(dentry);
+               if (IS_ERR(mp)) {
+                       up_write(&namespace_sem);
+                       mutex_unlock(&dentry->d_inode->i_mutex);
+                       return mp;
+               }
+               return mp;
+       }
        up_write(&namespace_sem);
        mutex_unlock(&path->dentry->d_inode->i_mutex);
        path_put(path);
        path->mnt = mnt;
-       path->dentry = dget(mnt->mnt_root);
+       dentry = path->dentry = dget(mnt->mnt_root);
        goto retry;
 }
 
-static void unlock_mount(struct path *path)
+static void unlock_mount(struct mountpoint *where)
 {
+       struct dentry *dentry = where->m_dentry;
+       put_mountpoint(where);
        up_write(&namespace_sem);
-       mutex_unlock(&path->dentry->d_inode->i_mutex);
+       mutex_unlock(&dentry->d_inode->i_mutex);
 }
 
-static int graft_tree(struct mount *mnt, struct path *path)
+static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
 {
        if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
                return -EINVAL;
 
-       if (S_ISDIR(path->dentry->d_inode->i_mode) !=
+       if (S_ISDIR(mp->m_dentry->d_inode->i_mode) !=
              S_ISDIR(mnt->mnt.mnt_root->d_inode->i_mode))
                return -ENOTDIR;
 
-       if (d_unlinked(path->dentry))
-               return -ENOENT;
-
-       return attach_recursive_mnt(mnt, path, NULL);
+       return attach_recursive_mnt(mnt, p, mp, NULL);
 }
 
 /*
@@ -1654,7 +1688,8 @@ static int do_loopback(struct path *path, const char *old_name,
 {
        LIST_HEAD(umount_list);
        struct path old_path;
-       struct mount *mnt = NULL, *old;
+       struct mount *mnt = NULL, *old, *parent;
+       struct mountpoint *mp;
        int err;
        if (!old_name || !*old_name)
                return -EINVAL;
@@ -1666,17 +1701,19 @@ static int do_loopback(struct path *path, const char *old_name,
        if (mnt_ns_loop(&old_path))
                goto out; 
 
-       err = lock_mount(path);
-       if (err)
+       mp = lock_mount(path);
+       err = PTR_ERR(mp);
+       if (IS_ERR(mp))
                goto out;
 
        old = real_mount(old_path.mnt);
+       parent = real_mount(path->mnt);
 
        err = -EINVAL;
        if (IS_MNT_UNBINDABLE(old))
                goto out2;
 
-       if (!check_mnt(real_mount(path->mnt)) || !check_mnt(old))
+       if (!check_mnt(parent) || !check_mnt(old))
                goto out2;
 
        if (recurse)
@@ -1689,14 +1726,14 @@ static int do_loopback(struct path *path, const char *old_name,
                goto out2;
        }
 
-       err = graft_tree(mnt, path);
+       err = graft_tree(mnt, parent, mp);
        if (err) {
                br_write_lock(&vfsmount_lock);
                umount_tree(mnt, 0, &umount_list);
                br_write_unlock(&vfsmount_lock);
        }
 out2:
-       unlock_mount(path);
+       unlock_mount(mp);
        release_mounts(&umount_list);
 out:
        path_put(&old_path);
@@ -1779,6 +1816,7 @@ static int do_move_mount(struct path *path, const char *old_name)
        struct path old_path, parent_path;
        struct mount *p;
        struct mount *old;
+       struct mountpoint *mp;
        int err;
        if (!old_name || !*old_name)
                return -EINVAL;
@@ -1786,8 +1824,9 @@ static int do_move_mount(struct path *path, const char *old_name)
        if (err)
                return err;
 
-       err = lock_mount(path);
-       if (err < 0)
+       mp = lock_mount(path);
+       err = PTR_ERR(mp);
+       if (IS_ERR(mp))
                goto out;
 
        old = real_mount(old_path.mnt);
@@ -1797,9 +1836,6 @@ static int do_move_mount(struct path *path, const char *old_name)
        if (!check_mnt(p) || !check_mnt(old))
                goto out1;
 
-       if (d_unlinked(path->dentry))
-               goto out1;
-
        err = -EINVAL;
        if (old_path.dentry != old_path.mnt->mnt_root)
                goto out1;
@@ -1826,7 +1862,7 @@ static int do_move_mount(struct path *path, const char *old_name)
                if (p == old)
                        goto out1;
 
-       err = attach_recursive_mnt(old, path, &parent_path);
+       err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
        if (err)
                goto out1;
 
@@ -1834,7 +1870,7 @@ static int do_move_mount(struct path *path, const char *old_name)
         * automatically */
        list_del_init(&old->mnt_expire);
 out1:
-       unlock_mount(path);
+       unlock_mount(mp);
 out:
        if (!err)
                path_put(&parent_path);
@@ -1870,21 +1906,24 @@ static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
  */
 static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
 {
+       struct mountpoint *mp;
+       struct mount *parent;
        int err;
 
        mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
 
-       err = lock_mount(path);
-       if (err)
-               return err;
+       mp = lock_mount(path);
+       if (IS_ERR(mp))
+               return PTR_ERR(mp);
 
+       parent = real_mount(path->mnt);
        err = -EINVAL;
-       if (unlikely(!check_mnt(real_mount(path->mnt)))) {
+       if (unlikely(!check_mnt(parent))) {
                /* that's acceptable only for automounts done in private ns */
                if (!(mnt_flags & MNT_SHRINKABLE))
                        goto unlock;
                /* ... and for those we'd better have mountpoint still alive */
-               if (!real_mount(path->mnt)->mnt_ns)
+               if (!parent->mnt_ns)
                        goto unlock;
        }
 
@@ -1899,10 +1938,10 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
                goto unlock;
 
        newmnt->mnt.mnt_flags = mnt_flags;
-       err = graft_tree(newmnt, path);
+       err = graft_tree(newmnt, parent, mp);
 
 unlock:
-       unlock_mount(path);
+       unlock_mount(mp);
        return err;
 }
 
@@ -2543,7 +2582,8 @@ 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;
+       struct mount *new_mnt, *root_mnt, *old_mnt;
+       struct mountpoint *old_mp, *root_mp;
        int error;
 
        if (!may_mount())
@@ -2562,14 +2602,16 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                goto out2;
 
        get_fs_root(current->fs, &root);
-       error = lock_mount(&old);
-       if (error)
+       old_mp = lock_mount(&old);
+       error = PTR_ERR(old_mp);
+       if (IS_ERR(old_mp))
                goto out3;
 
        error = -EINVAL;
        new_mnt = real_mount(new.mnt);
        root_mnt = real_mount(root.mnt);
-       if (IS_MNT_SHARED(real_mount(old.mnt)) ||
+       old_mnt = real_mount(old.mnt);
+       if (IS_MNT_SHARED(old_mnt) ||
                IS_MNT_SHARED(new_mnt->mnt_parent) ||
                IS_MNT_SHARED(root_mnt->mnt_parent))
                goto out4;
@@ -2578,37 +2620,37 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
        error = -ENOENT;
        if (d_unlinked(new.dentry))
                goto out4;
-       if (d_unlinked(old.dentry))
-               goto out4;
        error = -EBUSY;
-       if (new.mnt == root.mnt ||
-           old.mnt == root.mnt)
+       if (new_mnt == root_mnt || old_mnt == root_mnt)
                goto out4; /* loop, on the same file system  */
        error = -EINVAL;
        if (root.mnt->mnt_root != root.dentry)
                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))
                goto out4; /* not attached */
        /* make sure we can reach put_old from new_root */
-       if (!is_path_reachable(real_mount(old.mnt), old.dentry, &new))
+       if (!is_path_reachable(old_mnt, old.dentry, &new))
                goto out4;
+       root_mp->m_count++; /* pin it so it won't go away */
        br_write_lock(&vfsmount_lock);
        detach_mnt(new_mnt, &parent_path);
        detach_mnt(root_mnt, &root_parent);
        /* mount old root on put_old */
-       attach_mnt(root_mnt, &old);
+       attach_mnt(root_mnt, old_mnt, old_mp);
        /* mount new_root on / */
-       attach_mnt(new_mnt, &root_parent);
+       attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
        touch_mnt_namespace(current->nsproxy->mnt_ns);
        br_write_unlock(&vfsmount_lock);
        chroot_fs_refs(&root, &new);
+       put_mountpoint(root_mp);
        error = 0;
 out4:
-       unlock_mount(&old);
+       unlock_mount(old_mp);
        if (!error) {
                path_put(&root_parent);
                path_put(&parent_path);
@@ -2663,14 +2705,17 @@ void __init mnt_init(void)
                        0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 
        mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
+       mountpoint_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
 
-       if (!mount_hashtable)
+       if (!mount_hashtable || !mountpoint_hashtable)
                panic("Failed to allocate mount hash table\n");
 
        printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
 
        for (u = 0; u < HASH_SIZE; u++)
                INIT_LIST_HEAD(&mount_hashtable[u]);
+       for (u = 0; u < HASH_SIZE; u++)
+               INIT_LIST_HEAD(&mountpoint_hashtable[u]);
 
        br_lock_init(&vfsmount_lock);
 

diff --git a/fs/pnode.c b/fs/pnode.c
index 3e000a51ac0d09556d184d26422a91d0bc4c0ff9..98e0d3a23fac725f31fb807842a42ac148289f67 100644 (file)
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -217,7 +217,7 @@ static struct mount *get_source(struct mount *dest,
  * @source_mnt: source mount.
  * @tree_list : list of heads of trees to be attached.
  */
-int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
+int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
                    struct mount *source_mnt, struct list_head *tree_list)
 {
        struct mount *m, *child;
@@ -244,8 +244,8 @@ int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
                        goto out;
                }
 
-               if (is_subdir(dest_dentry, m->mnt.mnt_root)) {
-                       mnt_set_mountpoint(m, dest_dentry, child);
+               if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) {
+                       mnt_set_mountpoint(m, dest_mp, child);
                        list_add_tail(&child->mnt_hash, tree_list);
                } else {
                        /*

diff --git a/fs/pnode.h b/fs/pnode.h
index 19b853a3445cb907665b4403484984a0c525af68..f4357d3a0a4490da48e7024c0ca265e7b66c21a5 100644 (file)
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -31,14 +31,14 @@ static inline void set_mnt_shared(struct mount *mnt)
 }
 
 void change_mnt_propagation(struct mount *, int);
-int propagate_mnt(struct mount *, struct dentry *, struct mount *,
+int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
                struct list_head *);
 int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct mount *, int);
 void mnt_release_group_id(struct mount *);
 int get_dominating_id(struct mount *mnt, const struct path *root);
 unsigned int mnt_get_count(struct mount *mnt);
-void mnt_set_mountpoint(struct mount *, struct dentry *,
+void mnt_set_mountpoint(struct mount *, struct mountpoint *,
                        struct mount *);
 void release_mounts(struct list_head *);
 void umount_tree(struct mount *, int, struct list_head *);