Merge branch 'linus' into xen-64bit

1 files changed, 106 insertions, 41 deletions

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index a48dc7dd8765..0e64312a084c 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);