1 files changed, 106 insertions, 41 deletions

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index a48dc7d..0e64312 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -30,11 +30,25 @@
 #include <linux/mount.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/err.h>
 
 #include <linux/configfs.h>
 #include "configfs_internal.h"
 
 DECLARE_RWSEM(configfs_rename_sem);
+/*
+ * Protects mutations of configfs_dirent linkage together with proper i_mutex
+ * Also protects mutations of symlinks linkage to target configfs_dirent
+ * Mutators of configfs_dirent linkage must *both* have the proper inode locked
+ * and configfs_dirent_lock locked, in that order.
+ * This allows one to safely traverse configfs_dirent trees and symlinks without
+ * having to lock inodes.
+ *
+ * Protects setting of CONFIGFS_USET_DROPPING: checking the flag
+ * unlocked is not reliable unless in detach_groups() called from
+ * rmdir()/unregister() and from configfs_attach_group()
+ */
+DEFINE_SPINLOCK(configfs_dirent_lock);
 
 static void configfs_d_iput(struct dentry * dentry,
 			    struct inode * inode)
@@ -74,13 +88,20 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare
 
 	sd = kmem_cache_zalloc(configfs_dir_cachep, GFP_KERNEL);
 	if (!sd)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	atomic_set(&sd->s_count, 1);
 	INIT_LIST_HEAD(&sd->s_links);
 	INIT_LIST_HEAD(&sd->s_children);
-	list_add(&sd->s_sibling, &parent_sd->s_children);
 	sd->s_element = element;
+	spin_lock(&configfs_dirent_lock);
+	if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
+		spin_unlock(&configfs_dirent_lock);
+		kmem_cache_free(configfs_dir_cachep, sd);
+		return ERR_PTR(-ENOENT);
+	}
+	list_add(&sd->s_sibling, &parent_sd->s_children);
+	spin_unlock(&configfs_dirent_lock);
 
 	return sd;
 }
@@ -118,8 +139,8 @@ int configfs_make_dirent(struct configfs_dirent * parent_sd,
 	struct configfs_dirent * sd;
 
 	sd = configfs_new_dirent(parent_sd, element);
-	if (!sd)
-		return -ENOMEM;
+	if (IS_ERR(sd))
+		return PTR_ERR(sd);
 
 	sd->s_mode = mode;
 	sd->s_type = type;
@@ -173,7 +194,9 @@ static int create_dir(struct config_item * k, struct dentry * p,
 		} else {
 			struct configfs_dirent *sd = d->d_fsdata;
 			if (sd) {
+				spin_lock(&configfs_dirent_lock);
 				list_del_init(&sd->s_sibling);
+				spin_unlock(&configfs_dirent_lock);
 				configfs_put(sd);
 			}
 		}
@@ -224,7 +247,9 @@ int configfs_create_link(struct configfs_symlink *sl,
 		else {
 			struct configfs_dirent *sd = dentry->d_fsdata;
 			if (sd) {
+				spin_lock(&configfs_dirent_lock);
 				list_del_init(&sd->s_sibling);
+				spin_unlock(&configfs_dirent_lock);
 				configfs_put(sd);
 			}
 		}
@@ -238,7 +263,9 @@ static void remove_dir(struct dentry * d)
 	struct configfs_dirent * sd;
 
 	sd = d->d_fsdata;
+	spin_lock(&configfs_dirent_lock);
 	list_del_init(&sd->s_sibling);
+	spin_unlock(&configfs_dirent_lock);
 	configfs_put(sd);
 	if (d->d_inode)
 		simple_rmdir(parent->d_inode,d);
@@ -331,13 +358,13 @@ static struct dentry * configfs_lookup(struct inode *dir,
 
 /*
  * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
- * attributes and are removed by rmdir().  We recurse, taking i_mutex
- * on all children that are candidates for default detach.  If the
- * result is clean, then configfs_detach_group() will handle dropping
- * i_mutex.  If there is an error, the caller will clean up the i_mutex
- * holders via configfs_detach_rollback().
+ * attributes and are removed by rmdir().  We recurse, setting
+ * CONFIGFS_USET_DROPPING on all children that are candidates for
+ * default detach.
+ * If there is an error, the caller will reset the flags via
+ * configfs_detach_rollback().
  */
-static int configfs_detach_prep(struct dentry *dentry)
+static int configfs_detach_prep(struct dentry *dentry, struct mutex **wait_mutex)
 {
 	struct configfs_dirent *parent_sd = dentry->d_fsdata;
 	struct configfs_dirent *sd;
@@ -352,15 +379,20 @@ static int configfs_detach_prep(struct dentry *dentry)
 		if (sd->s_type & CONFIGFS_NOT_PINNED)
 			continue;
 		if (sd->s_type & CONFIGFS_USET_DEFAULT) {
-			mutex_lock(&sd->s_dentry->d_inode->i_mutex);
-			/* Mark that we've taken i_mutex */
+			/* Abort if racing with mkdir() */
+			if (sd->s_type & CONFIGFS_USET_IN_MKDIR) {
+				if (wait_mutex)
+					*wait_mutex = &sd->s_dentry->d_inode->i_mutex;
+				return -EAGAIN;
+			}
+			/* Mark that we're trying to drop the group */
 			sd->s_type |= CONFIGFS_USET_DROPPING;
 
 			/*
 			 * Yup, recursive.  If there's a problem, blame
 			 * deep nesting of default_groups
 			 */
-			ret = configfs_detach_prep(sd->s_dentry);
+			ret = configfs_detach_prep(sd->s_dentry, wait_mutex);
 			if (!ret)
 				continue;
 		} else
@@ -374,7 +406,7 @@ out:
 }
 
 /*
- * Walk the tree, dropping i_mutex wherever CONFIGFS_USET_DROPPING is
+ * Walk the tree, resetting CONFIGFS_USET_DROPPING wherever it was
  * set.
  */
 static void configfs_detach_rollback(struct dentry *dentry)
@@ -385,11 +417,7 @@ static void configfs_detach_rollback(struct dentry *dentry)
 	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
 		if (sd->s_type & CONFIGFS_USET_DEFAULT) {
 			configfs_detach_rollback(sd->s_dentry);
-
-			if (sd->s_type & CONFIGFS_USET_DROPPING) {
-				sd->s_type &= ~CONFIGFS_USET_DROPPING;
-				mutex_unlock(&sd->s_dentry->d_inode->i_mutex);
-			}
+			sd->s_type &= ~CONFIGFS_USET_DROPPING;
 		}
 	}
 }
@@ -410,7 +438,9 @@ static void detach_attrs(struct config_item * item)
 	list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
 		if (!sd->s_element || !(sd->s_type & CONFIGFS_NOT_PINNED))
 			continue;
+		spin_lock(&configfs_dirent_lock);
 		list_del_init(&sd->s_sibling);
+		spin_unlock(&configfs_dirent_lock);
 		configfs_drop_dentry(sd, dentry);
 		configfs_put(sd);
 	}
@@ -466,16 +496,12 @@ static void detach_groups(struct config_group *group)
 
 		child = sd->s_dentry;
 
+		mutex_lock(&child->d_inode->i_mutex);
+
 		configfs_detach_group(sd->s_element);
 		child->d_inode->i_flags |= S_DEAD;
 
-		/*
-		 * From rmdir/unregister, a configfs_detach_prep() pass
-		 * has taken our i_mutex for us.  Drop it.
-		 * From mkdir/register cleanup, there is no sem held.
-		 */
-		if (sd->s_type & CONFIGFS_USET_DROPPING)
-			mutex_unlock(&child->d_inode->i_mutex);
+		mutex_unlock(&child->d_inode->i_mutex);
 
 		d_delete(child);
 		dput(child);
@@ -1047,25 +1073,24 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	group = NULL;
 	item = NULL;
 	if (type->ct_group_ops->make_group) {
-		group = type->ct_group_ops->make_group(to_config_group(parent_item), name);
-		if (group) {
+		ret = type->ct_group_ops->make_group(to_config_group(parent_item), name, &group);
+		if (!ret) {
 			link_group(to_config_group(parent_item), group);
 			item = &group->cg_item;
 		}
 	} else {
-		item = type->ct_group_ops->make_item(to_config_group(parent_item), name);
-		if (item)
+		ret = type->ct_group_ops->make_item(to_config_group(parent_item), name, &item);
+		if (!ret)
 			link_obj(parent_item, item);
 	}
 	mutex_unlock(&subsys->su_mutex);
 
 	kfree(name);
-	if (!item) {
+	if (ret) {
 		/*
-		 * If item == NULL, then link_obj() was never called.
+		 * If ret != 0, then link_obj() was never called.
 		 * There are no extra references to clean up.
 		 */
-		ret = -ENOMEM;
 		goto out_put;
 	}
 
@@ -1093,11 +1118,26 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	 */
 	module_got = 1;
 
+	/*
+	 * Make racing rmdir() fail if it did not tag parent with
+	 * CONFIGFS_USET_DROPPING
+	 * Note: if CONFIGFS_USET_DROPPING is already set, attach_group() will
+	 * fail and let rmdir() terminate correctly
+	 */
+	spin_lock(&configfs_dirent_lock);
+	/* This will make configfs_detach_prep() fail */
+	sd->s_type |= CONFIGFS_USET_IN_MKDIR;
+	spin_unlock(&configfs_dirent_lock);
+
 	if (group)
 		ret = configfs_attach_group(parent_item, item, dentry);
 	else
 		ret = configfs_attach_item(parent_item, item, dentry);
 
+	spin_lock(&configfs_dirent_lock);
+	sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
+	spin_unlock(&configfs_dirent_lock);
+
 out_unlink:
 	if (ret) {
 		/* Tear down everything we built up */
@@ -1161,12 +1201,27 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 		return -EINVAL;
 	}
 
-	ret = configfs_detach_prep(dentry);
-	if (ret) {
-		configfs_detach_rollback(dentry);
-		config_item_put(parent_item);
-		return ret;
-	}
+	spin_lock(&configfs_dirent_lock);
+	do {
+		struct mutex *wait_mutex;
+
+		ret = configfs_detach_prep(dentry, &wait_mutex);
+		if (ret) {
+			configfs_detach_rollback(dentry);
+			spin_unlock(&configfs_dirent_lock);
+			if (ret != -EAGAIN) {
+				config_item_put(parent_item);
+				return ret;
+			}
+
+			/* Wait until the racing operation terminates */
+			mutex_lock(wait_mutex);
+			mutex_unlock(wait_mutex);
+
+			spin_lock(&configfs_dirent_lock);
+		}
+	} while (ret == -EAGAIN);
+	spin_unlock(&configfs_dirent_lock);
 
 	/* Get a working ref for the duration of this function */
 	item = configfs_get_config_item(dentry);
@@ -1258,7 +1313,7 @@ static int configfs_dir_open(struct inode *inode, struct file *file)
 	file->private_data = configfs_new_dirent(parent_sd, NULL);
 	mutex_unlock(&dentry->d_inode->i_mutex);
 
-	return file->private_data ? 0 : -ENOMEM;
+	return IS_ERR(file->private_data) ? PTR_ERR(file->private_data) : 0;
 
 }
 
@@ -1268,7 +1323,9 @@ static int configfs_dir_close(struct inode *inode, struct file *file)
 	struct configfs_dirent * cursor = file->private_data;
 
 	mutex_lock(&dentry->d_inode->i_mutex);
+	spin_lock(&configfs_dirent_lock);
 	list_del_init(&cursor->s_sibling);
+	spin_unlock(&configfs_dirent_lock);
 	mutex_unlock(&dentry->d_inode->i_mutex);
 
 	release_configfs_dirent(cursor);
@@ -1308,7 +1365,9 @@ static int configfs_readdir(struct file * filp, void * dirent, filldir_t filldir
 			/* fallthrough */
 		default:
 			if (filp->f_pos == 2) {
+				spin_lock(&configfs_dirent_lock);
 				list_move(q, &parent_sd->s_children);
+				spin_unlock(&configfs_dirent_lock);
 			}
 			for (p=q->next; p!= &parent_sd->s_children; p=p->next) {
 				struct configfs_dirent *next;
@@ -1331,7 +1390,9 @@ static int configfs_readdir(struct file * filp, void * dirent, filldir_t filldir
 						 dt_type(next)) < 0)
 					return 0;
 
+				spin_lock(&configfs_dirent_lock);
 				list_move(q, p);
+				spin_unlock(&configfs_dirent_lock);
 				p = q;
 				filp->f_pos++;
 			}
@@ -1362,6 +1423,7 @@ static loff_t configfs_dir_lseek(struct file * file, loff_t offset, int origin)
 			struct list_head *p;
 			loff_t n = file->f_pos - 2;
 
+			spin_lock(&configfs_dirent_lock);
 			list_del(&cursor->s_sibling);
 			p = sd->s_children.next;
 			while (n && p != &sd->s_children) {
@@ -1373,6 +1435,7 @@ static loff_t configfs_dir_lseek(struct file * file, loff_t offset, int origin)
 				p = p->next;
 			}
 			list_add_tail(&cursor->s_sibling, p);
+			spin_unlock(&configfs_dirent_lock);
 		}
 	}
 	mutex_unlock(&dentry->d_inode->i_mutex);
@@ -1448,9 +1511,11 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
 	mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex,
 			  I_MUTEX_PARENT);
 	mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
-	if (configfs_detach_prep(dentry)) {
+	spin_lock(&configfs_dirent_lock);
+	if (configfs_detach_prep(dentry, NULL)) {
 		printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");
 	}
+	spin_unlock(&configfs_dirent_lock);
 	configfs_detach_group(&group->cg_item);
 	dentry->d_inode->i_flags |= S_DEAD;
 	mutex_unlock(&dentry->d_inode->i_mutex);