1 files changed, 241 insertions, 41 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 2355bddad8de..fd4a428998ef 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -478,11 +478,12 @@ static void prune_dcache(int count, struct super_block *sb)
                         up_read(s_umount);
                 }
                 spin_unlock(&dentry->d_lock);
-                /* Cannot remove the first dentry, and it isn't appropriate
-                 * to move it to the head of the list, so give up, and try
-                 * later
+                /*
+                 * Insert dentry at the head of the list as inserting at the
+                 * tail leads to a cycle.
                  */
-                break;
+                list_add(&dentry->d_lru, &dentry_unused);
+                dentry_stat.nr_unused++;
         }
         spin_unlock(&dcache_lock);
 }
@@ -549,6 +550,142 @@ repeat:
 }
 
 /*
+ * destroy a single subtree of dentries for unmount
+ * - see the comments on shrink_dcache_for_umount() for a description of the
+ *   locking
+ */
+static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
+{
+        struct dentry *parent;
+        unsigned detached = 0;
+
+        BUG_ON(!IS_ROOT(dentry));
+
+        /* detach this root from the system */
+        spin_lock(&dcache_lock);
+        if (!list_empty(&dentry->d_lru)) {
+                dentry_stat.nr_unused--;
+                list_del_init(&dentry->d_lru);
+        }
+        __d_drop(dentry);
+        spin_unlock(&dcache_lock);
+
+        for (;;) {
+                /* descend to the first leaf in the current subtree */
+                while (!list_empty(&dentry->d_subdirs)) {
+                        struct dentry *loop;
+
+                        /* this is a branch with children - detach all of them
+                         * from the system in one go */
+                        spin_lock(&dcache_lock);
+                        list_for_each_entry(loop, &dentry->d_subdirs,
+                                            d_u.d_child) {
+                                if (!list_empty(&loop->d_lru)) {
+                                        dentry_stat.nr_unused--;
+                                        list_del_init(&loop->d_lru);
+                                }
+
+                                __d_drop(loop);
+                                cond_resched_lock(&dcache_lock);
+                        }
+                        spin_unlock(&dcache_lock);
+
+                        /* move to the first child */
+                        dentry = list_entry(dentry->d_subdirs.next,
+                                            struct dentry, d_u.d_child);
+                }
+
+                /* consume the dentries from this leaf up through its parents
+                 * until we find one with children or run out altogether */
+                do {
+                        struct inode *inode;
+
+                        if (atomic_read(&dentry->d_count) != 0) {
+                                printk(KERN_ERR
+                                       "BUG: Dentry %p{i=%lx,n=%s}"
+                                       " still in use (%d)"
+                                       " [unmount of %s %s]\n",
+                                       dentry,
+                                       dentry->d_inode ?
+                                       dentry->d_inode->i_ino : 0UL,
+                                       dentry->d_name.name,
+                                       atomic_read(&dentry->d_count),
+                                       dentry->d_sb->s_type->name,
+                                       dentry->d_sb->s_id);
+                                BUG();
+                        }
+
+                        parent = dentry->d_parent;
+                        if (parent == dentry)
+                                parent = NULL;
+                        else
+                                atomic_dec(&parent->d_count);
+
+                        list_del(&dentry->d_u.d_child);
+                        detached++;
+
+                        inode = dentry->d_inode;
+                        if (inode) {
+                                dentry->d_inode = NULL;
+                                list_del_init(&dentry->d_alias);
+                                if (dentry->d_op && dentry->d_op->d_iput)
+                                        dentry->d_op->d_iput(dentry, inode);
+                                else
+                                        iput(inode);
+                        }
+
+                        d_free(dentry);
+
+                        /* finished when we fall off the top of the tree,
+                         * otherwise we ascend to the parent and move to the
+                         * next sibling if there is one */
+                        if (!parent)
+                                goto out;
+
+                        dentry = parent;
+
+                } while (list_empty(&dentry->d_subdirs));
+
+                dentry = list_entry(dentry->d_subdirs.next,
+                                    struct dentry, d_u.d_child);
+        }
+out:
+        /* several dentries were freed, need to correct nr_dentry */
+        spin_lock(&dcache_lock);
+        dentry_stat.nr_dentry -= detached;
+        spin_unlock(&dcache_lock);
+}
+
+/*
+ * destroy the dentries attached to a superblock on unmounting
+ * - we don't need to use dentry->d_lock, and only need dcache_lock when
+ *   removing the dentry from the system lists and hashes because:
+ *   - the superblock is detached from all mountings and open files, so the
+ *     dentry trees will not be rearranged by the VFS
+ *   - s_umount is write-locked, so the memory pressure shrinker will ignore
+ *     any dentries belonging to this superblock that it comes across
+ *   - the filesystem itself is no longer permitted to rearrange the dentries
+ *     in this superblock
+ */
+void shrink_dcache_for_umount(struct super_block *sb)
+{
+        struct dentry *dentry;
+
+        if (down_read_trylock(&sb->s_umount))
+                BUG();
+
+        dentry = sb->s_root;
+        sb->s_root = NULL;
+        atomic_dec(&dentry->d_count);
+        shrink_dcache_for_umount_subtree(dentry);
+
+        while (!hlist_empty(&sb->s_anon)) {
+                dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
+                shrink_dcache_for_umount_subtree(dentry);
+        }
+}
+
+/*
  * Search for at least 1 mount point in the dentry's subdirs.
  * We descend to the next level whenever the d_subdirs
  * list is non-empty and continue searching.
@@ -1339,23 +1476,21 @@ static void switch_names(struct dentry *dentry, struct dentry *target)
  * deleted it.
  */
  
-/**
- * d_move - move a dentry
+/*
+ * d_move_locked - move a dentry
  * @dentry: entry to move
  * @target: new dentry
  *
  * Update the dcache to reflect the move of a file name. Negative
  * dcache entries should not be moved in this way.
  */
-
-void d_move(struct dentry * dentry, struct dentry * target)
+static void d_move_locked(struct dentry * dentry, struct dentry * target)
 {
         struct hlist_head *list;
 
         if (!dentry->d_inode)
                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
 
-        spin_lock(&dcache_lock);
         write_seqlock(&rename_lock);
         /*
          * XXXX: do we really need to take target->d_lock?
@@ -1406,7 +1541,81 @@ already_unhashed:
         fsnotify_d_move(dentry);
         spin_unlock(&dentry->d_lock);
         write_sequnlock(&rename_lock);
+}
+
+/**
+ * d_move - move a dentry
+ * @dentry: entry to move
+ * @target: new dentry
+ *
+ * Update the dcache to reflect the move of a file name. Negative
+ * dcache entries should not be moved in this way.
+ */
+
+void d_move(struct dentry * dentry, struct dentry * target)
+{
+        spin_lock(&dcache_lock);
+        d_move_locked(dentry, target);
+        spin_unlock(&dcache_lock);
+}
+
+/*
+ * Helper that returns 1 if p1 is a parent of p2, else 0
+ */
+static int d_isparent(struct dentry *p1, struct dentry *p2)
+{
+        struct dentry *p;
+
+        for (p = p2; p->d_parent != p; p = p->d_parent) {
+                if (p->d_parent == p1)
+                        return 1;
+        }
+        return 0;
+}
+
+/*
+ * This helper attempts to cope with remotely renamed directories
+ *
+ * It assumes that the caller is already holding
+ * dentry->d_parent->d_inode->i_mutex and the dcache_lock
+ *
+ * Note: If ever the locking in lock_rename() changes, then please
+ * remember to update this too...
+ *
+ * On return, dcache_lock will have been unlocked.
+ */
+static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias)
+{
+        struct mutex *m1 = NULL, *m2 = NULL;
+        struct dentry *ret;
+
+        /* If alias and dentry share a parent, then no extra locks required */
+        if (alias->d_parent == dentry->d_parent)
+                goto out_unalias;
+
+        /* Check for loops */
+        ret = ERR_PTR(-ELOOP);
+        if (d_isparent(alias, dentry))
+                goto out_err;
+
+        /* See lock_rename() */
+        ret = ERR_PTR(-EBUSY);
+        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
+                goto out_err;
+        m1 = &dentry->d_sb->s_vfs_rename_mutex;
+        if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
+                goto out_err;
+        m2 = &alias->d_parent->d_inode->i_mutex;
+out_unalias:
+        d_move_locked(alias, dentry);
+        ret = alias;
+out_err:
         spin_unlock(&dcache_lock);
+        if (m2)
+                mutex_unlock(m2);
+        if (m1)
+                mutex_unlock(m1);
+        return ret;
 }
 
 /*
@@ -1451,7 +1660,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
  */
 struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
 {
-        struct dentry *alias, *actual;
+        struct dentry *actual;
 
         BUG_ON(!d_unhashed(dentry));
 
@@ -1463,26 +1672,27 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
                 goto found_lock;
         }
 
-        /* See if a disconnected directory already exists as an anonymous root
-         * that we should splice into the tree instead */
-        if (S_ISDIR(inode->i_mode) && (alias = __d_find_alias(inode, 1))) {
-                spin_lock(&alias->d_lock);
-
-                /* Is this a mountpoint that we could splice into our tree? */
-                if (IS_ROOT(alias))
-                        goto connect_mountpoint;
-
-                if (alias->d_name.len == dentry->d_name.len &&
-                    alias->d_parent == dentry->d_parent &&
-                    memcmp(alias->d_name.name,
-                           dentry->d_name.name,
-                           dentry->d_name.len) == 0)
-                        goto replace_with_alias;
-
-                spin_unlock(&alias->d_lock);
-
-                /* Doh! Seem to be aliasing directories for some reason... */
-                dput(alias);
+        if (S_ISDIR(inode->i_mode)) {
+                struct dentry *alias;
+
+                /* Does an aliased dentry already exist? */
+                alias = __d_find_alias(inode, 0);
+                if (alias) {
+                        actual = alias;
+                        /* Is this an anonymous mountpoint that we could splice
+                         * into our tree? */
+                        if (IS_ROOT(alias)) {
+                                spin_lock(&alias->d_lock);
+                                __d_materialise_dentry(dentry, alias);
+                                __d_drop(alias);
+                                goto found;
+                        }
+                        /* Nope, but we must(!) avoid directory aliasing */
+                        actual = __d_unalias(dentry, alias);
+                        if (IS_ERR(actual))
+                                dput(alias);
+                        goto out_nolock;
+                }
         }
 
         /* Add a unique reference */
@@ -1498,7 +1708,7 @@ found:
         _d_rehash(actual);
         spin_unlock(&actual->d_lock);
         spin_unlock(&dcache_lock);
-
+out_nolock:
         if (actual == dentry) {
                 security_d_instantiate(dentry, inode);
                 return NULL;
@@ -1507,16 +1717,6 @@ found:
         iput(inode);
         return actual;
 
-        /* Convert the anonymous/root alias into an ordinary dentry */
-connect_mountpoint:
-        __d_materialise_dentry(dentry, alias);
-
-        /* Replace the candidate dentry with the alias in the tree */
-replace_with_alias:
-        __d_drop(alias);
-        actual = alias;
-        goto found;
-
 shouldnt_be_hashed:
         spin_unlock(&dcache_lock);
         BUG();