sysfs: Propagate renames to the vfs on demand

By teaching sysfs_revalidate to hide a dentry for
a sysfs_dirent if the sysfs_dirent has been renamed,
and by teaching sysfs_lookup to return the original
dentry if the sysfs dirent has been renamed.  I can
show the results of renames correctly without having to
update the dcache during the directory rename.

This massively simplifies the rename logic allowing a lot
of weird sysfs special cases to be removed along with
a lot of now unnecesary helper code.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

4 files changed, 32 insertions, 161 deletions

diff --git a/fs/namei.c b/fs/namei.c
index d11f404667e9..d3c190c35fcc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1279,28 +1279,6 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
         return __lookup_hash(&this, base, NULL);
 }
 
-/**
- * lookup_one_noperm - bad hack for sysfs
- * @name:       pathname component to lookup
- * @base:       base directory to lookup from
- *
- * This is a variant of lookup_one_len that doesn't perform any permission
- * checks.   It's a horrible hack to work around the braindead sysfs
- * architecture and should not be used anywhere else.
- *
- * DON'T USE THIS FUNCTION EVER, thanks.
- */
-struct dentry *lookup_one_noperm(const char *name, struct dentry *base)
-{
-        int err;
-        struct qstr this;
-
-        err = __lookup_one_len(name, &this, base, strlen(name));
-        if (err)
-                return ERR_PTR(err);
-        return __lookup_hash(&this, base, NULL);
-}
-
 int user_path_at(int dfd, const char __user *name, unsigned flags,
                  struct path *path)
 {
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index f3af45e47eaa..97954c69ff0e 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -25,7 +25,6 @@
 #include "sysfs.h"
 
 DEFINE_MUTEX(sysfs_mutex);
-DEFINE_MUTEX(sysfs_rename_mutex);
 DEFINE_SPINLOCK(sysfs_assoc_lock);
 
 static DEFINE_SPINLOCK(sysfs_ino_lock);
@@ -85,46 +84,6 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
 }
 
 /**
- *      sysfs_get_dentry - get dentry for the given sysfs_dirent
- *      @sd: sysfs_dirent of interest
- *
- *      Get dentry for @sd.  Dentry is looked up if currently not
- *      present.  This function descends from the root looking up
- *      dentry for each step.
- *
- *      LOCKING:
- *      mutex_lock(sysfs_rename_mutex)
- *
- *      RETURNS:
- *      Pointer to found dentry on success, ERR_PTR() value on error.
- */
-struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd)
-{
-        struct dentry *dentry = dget(sysfs_sb->s_root);
-
-        while (dentry->d_fsdata != sd) {
-                struct sysfs_dirent *cur;
-                struct dentry *parent;
-
-                /* find the first ancestor which hasn't been looked up */
-                cur = sd;
-                while (cur->s_parent != dentry->d_fsdata)
-                        cur = cur->s_parent;
-
-                /* look it up */
-                parent = dentry;
-                mutex_lock(&parent->d_inode->i_mutex);
-                dentry = lookup_one_noperm(cur->s_name, parent);
-                mutex_unlock(&parent->d_inode->i_mutex);
-                dput(parent);
-
-                if (IS_ERR(dentry))
-                        break;
-        }
-        return dentry;
-}
-
-/**
  *      sysfs_get_active - get an active reference to sysfs_dirent
  *      @sd: sysfs_dirent to get an active reference to
  *
@@ -315,6 +274,14 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
         if (sd->s_flags & SYSFS_FLAG_REMOVED)
                 goto out_bad;
 
+        /* The sysfs dirent has been moved? */
+        if (dentry->d_parent->d_fsdata != sd->s_parent)
+                goto out_bad;
+
+        /* The sysfs dirent has been renamed */
+        if (strcmp(dentry->d_name.name, sd->s_name) != 0)
+                goto out_bad;
+
         mutex_unlock(&sysfs_mutex);
 out_valid:
         return 1;
@@ -322,6 +289,12 @@ out_bad:
         /* Remove the dentry from the dcache hashes.
          * If this is a deleted dentry we use d_drop instead of d_delete
          * so sysfs doesn't need to cope with negative dentries.
+         *
+         * If this is a dentry that has simply been renamed we
+         * use d_drop to remove it from the dcache lookup on its
+         * old parent.  If this dentry persists later when a lookup
+         * is performed at its new name the dentry will be readded
+         * to the dcache hashes.
          */
         is_dir = (sysfs_type(sd) == SYSFS_DIR);
         mutex_unlock(&sysfs_mutex);
@@ -705,10 +678,15 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
         }
 
         /* instantiate and hash dentry */
-        dentry->d_op = &sysfs_dentry_ops;
-        dentry->d_fsdata = sysfs_get(sd);
-        d_instantiate(dentry, inode);
-        d_rehash(dentry);
+        ret = d_find_alias(inode);
+        if (!ret) {
+                dentry->d_op = &sysfs_dentry_ops;
+                dentry->d_fsdata = sysfs_get(sd);
+                d_add(dentry, inode);
+        } else {
+                d_move(ret, dentry);
+                iput(inode);
+        }
 
  out_unlock:
         mutex_unlock(&sysfs_mutex);
@@ -785,62 +763,32 @@ void sysfs_remove_dir(struct kobject * kobj)
 int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
 {
         struct sysfs_dirent *sd = kobj->sd;
-        struct dentry *parent = NULL;
-        struct dentry *old_dentry = NULL, *new_dentry = NULL;
         const char *dup_name = NULL;
         int error;
 
-        mutex_lock(&sysfs_rename_mutex);
+        mutex_lock(&sysfs_mutex);
 
         error = 0;
         if (strcmp(sd->s_name, new_name) == 0)
                 goto out;       /* nothing to rename */
 
-        /* get the original dentry */
-        old_dentry = sysfs_get_dentry(sd);
-        if (IS_ERR(old_dentry)) {
-                error = PTR_ERR(old_dentry);
-                old_dentry = NULL;
-                goto out;
-        }
-
-        parent = old_dentry->d_parent;
-
-        /* lock parent and get dentry for new name */
-        mutex_lock(&parent->d_inode->i_mutex);
-        mutex_lock(&sysfs_mutex);
-
         error = -EEXIST;
         if (sysfs_find_dirent(sd->s_parent, new_name))
-                goto out_unlock;
-
-        error = -ENOMEM;
-        new_dentry = d_alloc_name(parent, new_name);
-        if (!new_dentry)
-                goto out_unlock;
+                goto out;
 
         /* rename sysfs_dirent */
         error = -ENOMEM;
         new_name = dup_name = kstrdup(new_name, GFP_KERNEL);
         if (!new_name)
-                goto out_unlock;
+                goto out;
 
         dup_name = sd->s_name;
         sd->s_name = new_name;
 
-        /* rename */
-        d_add(new_dentry, NULL);
-        d_move(old_dentry, new_dentry);
-
         error = 0;
- out_unlock:
+ out:
         mutex_unlock(&sysfs_mutex);
-        mutex_unlock(&parent->d_inode->i_mutex);
         kfree(dup_name);
-        dput(old_dentry);
-        dput(new_dentry);
- out:
-        mutex_unlock(&sysfs_rename_mutex);
         return error;
 }
 
@@ -848,12 +796,11 @@ int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
 {
         struct sysfs_dirent *sd = kobj->sd;
         struct sysfs_dirent *new_parent_sd;
-        struct dentry *old_parent, *new_parent = NULL;
-        struct dentry *old_dentry = NULL, *new_dentry = NULL;
         int error;
 
-        mutex_lock(&sysfs_rename_mutex);
         BUG_ON(!sd->s_parent);
+
+        mutex_lock(&sysfs_mutex);
         new_parent_sd = (new_parent_kobj && new_parent_kobj->sd) ?
                 new_parent_kobj->sd : &sysfs_root;
 
@@ -861,61 +808,20 @@ int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
         if (sd->s_parent == new_parent_sd)
                 goto out;       /* nothing to move */
 
-        /* get dentries */
-        old_dentry = sysfs_get_dentry(sd);
-        if (IS_ERR(old_dentry)) {
-                error = PTR_ERR(old_dentry);
-                old_dentry = NULL;
-                goto out;
-        }
-        old_parent = old_dentry->d_parent;
-
-        new_parent = sysfs_get_dentry(new_parent_sd);
-        if (IS_ERR(new_parent)) {
-                error = PTR_ERR(new_parent);
-                new_parent = NULL;
-                goto out;
-        }
-
-again:
-        mutex_lock(&old_parent->d_inode->i_mutex);
-        if (!mutex_trylock(&new_parent->d_inode->i_mutex)) {
-                mutex_unlock(&old_parent->d_inode->i_mutex);
-                goto again;
-        }
-        mutex_lock(&sysfs_mutex);
-
         error = -EEXIST;
         if (sysfs_find_dirent(new_parent_sd, sd->s_name))
-                goto out_unlock;
-
-        error = -ENOMEM;
-        new_dentry = d_alloc_name(new_parent, sd->s_name);
-        if (!new_dentry)
-                goto out_unlock;
-
-        error = 0;
-        d_add(new_dentry, NULL);
-        d_move(old_dentry, new_dentry);
+                goto out;
 
         /* Remove from old parent's list and insert into new parent's list. */
         sysfs_unlink_sibling(sd);
         sysfs_get(new_parent_sd);
-        drop_nlink(old_parent->d_inode);
         sysfs_put(sd->s_parent);
         sd->s_parent = new_parent_sd;
-        inc_nlink(new_parent->d_inode);
         sysfs_link_sibling(sd);
 
- out_unlock:
+        error = 0;
+out:
         mutex_unlock(&sysfs_mutex);
-        mutex_unlock(&new_parent->d_inode->i_mutex);
-        mutex_unlock(&old_parent->d_inode->i_mutex);
- out:
-        dput(new_parent);
-        dput(old_dentry);
-        dput(new_dentry);
-        mutex_unlock(&sysfs_rename_mutex);
         return error;
 }
 
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 1ffd5559926f..9f783d4e4b51 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -205,17 +205,6 @@ static inline void set_inode_attr(struct inode * inode, struct iattr * iattr)
         inode->i_ctime = iattr->ia_ctime;
 }
 
-
-/*
- * sysfs has a different i_mutex lock order behavior for i_mutex than other
- * filesystems; sysfs i_mutex is called in many places with subsystem locks
- * held. At the same time, many of the VFS locking rules do not apply to
- * sysfs at all (cross directory rename for example). To untangle this mess
- * (which gives false positives in lockdep), we're giving sysfs inodes their
- * own class for i_mutex.
- */
-static struct lock_class_key sysfs_inode_imutex_key;
-
 static int sysfs_count_nlink(struct sysfs_dirent *sd)
 {
         struct sysfs_dirent *child;
@@ -268,7 +257,6 @@ static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
         inode->i_mapping->a_ops = &sysfs_aops;
         inode->i_mapping->backing_dev_info = &sysfs_backing_dev_info;
         inode->i_op = &sysfs_inode_operations;
-        lockdep_set_class(&inode->i_mutex, &sysfs_inode_imutex_key);
 
         set_default_inode_attr(inode, sd->s_mode);
         sysfs_refresh_inode(sd, inode);
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 90b35012abb2..98a15bf1efe1 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -103,7 +103,6 @@ extern struct kmem_cache *sysfs_dir_cachep;
  * dir.c
  */
 extern struct mutex sysfs_mutex;
-extern struct mutex sysfs_rename_mutex;
 extern spinlock_t sysfs_assoc_lock;
 
 extern const struct file_operations sysfs_dir_operations;