1 files changed, 102 insertions, 21 deletions

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 60717660ac55..d998e8e27841 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -14,8 +14,14 @@ struct sysfs_elem_bin_attr {
 	struct bin_attribute	* bin_attr;
 };
 
+/*
+ * As long as s_count reference is held, the sysfs_dirent itself is
+ * accessible.  Dereferencing s_elem or any other outer entity
+ * requires s_active reference.
+ */
 struct sysfs_dirent {
 	atomic_t		s_count;
+	struct rw_semaphore	s_active;
 	struct sysfs_dirent	* s_parent;
 	struct list_head	s_sibling;
 	struct list_head	s_children;
@@ -36,6 +42,17 @@ struct sysfs_dirent {
 	atomic_t		s_event;
 };
 
+/*
+ * A sysfs file which deletes another file when written to need to
+ * write lock the s_active of the victim while its s_active is read
+ * locked for the write operation.  Tell lockdep that this is okay.
+ */
+enum sysfs_s_active_class
+{
+	SYSFS_S_ACTIVE_NORMAL,		/* file r/w access, etc - default */
+	SYSFS_S_ACTIVE_DEACTIVATE,	/* file deactivation */
+};
+
 extern struct vfsmount * sysfs_mount;
 extern struct kmem_cache *sysfs_dir_cachep;
 
@@ -87,43 +104,107 @@ struct sysfs_buffer_collection {
 	struct list_head	associates;
 };
 
-static inline struct kobject * to_kobj(struct dentry * dentry)
+static inline struct sysfs_dirent * sysfs_get(struct sysfs_dirent * sd)
 {
-	struct sysfs_dirent * sd = dentry->d_fsdata;
-	return sd->s_elem.dir.kobj;
+	if (sd) {
+		WARN_ON(!atomic_read(&sd->s_count));
+		atomic_inc(&sd->s_count);
+	}
+	return sd;
 }
 
-static inline struct kobject *sysfs_get_kobject(struct dentry *dentry)
+static inline void sysfs_put(struct sysfs_dirent * sd)
 {
-	struct kobject * kobj = NULL;
-
-	spin_lock(&dcache_lock);
-	if (!d_unhashed(dentry)) {
-		struct sysfs_dirent * sd = dentry->d_fsdata;
-
-		if (sd->s_type & SYSFS_KOBJ_LINK)
-			sd = sd->s_elem.symlink.target_sd;
+	if (sd && atomic_dec_and_test(&sd->s_count))
+		release_sysfs_dirent(sd);
+}
 
-		kobj = kobject_get(sd->s_elem.dir.kobj);
+/**
+ *	sysfs_get_active - get an active reference to sysfs_dirent
+ *	@sd: sysfs_dirent to get an active reference to
+ *
+ *	Get an active reference of @sd.  This function is noop if @sd
+ *	is NULL.
+ *
+ *	RETURNS:
+ *	Pointer to @sd on success, NULL on failure.
+ */
+static inline struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
+{
+	if (sd) {
+		if (unlikely(!down_read_trylock(&sd->s_active)))
+			sd = NULL;
 	}
-	spin_unlock(&dcache_lock);
+	return sd;
+}
 
-	return kobj;
+/**
+ *	sysfs_put_active - put an active reference to sysfs_dirent
+ *	@sd: sysfs_dirent to put an active reference to
+ *
+ *	Put an active reference to @sd.  This function is noop if @sd
+ *	is NULL.
+ */
+static inline void sysfs_put_active(struct sysfs_dirent *sd)
+{
+	if (sd)
+		up_read(&sd->s_active);
 }
 
-static inline struct sysfs_dirent * sysfs_get(struct sysfs_dirent * sd)
+/**
+ *	sysfs_get_active_two - get active references to sysfs_dirent and parent
+ *	@sd: sysfs_dirent of interest
+ *
+ *	Get active reference to @sd and its parent.  Parent's active
+ *	reference is grabbed first.  This function is noop if @sd is
+ *	NULL.
+ *
+ *	RETURNS:
+ *	Pointer to @sd on success, NULL on failure.
+ */
+static inline struct sysfs_dirent *sysfs_get_active_two(struct sysfs_dirent *sd)
 {
 	if (sd) {
-		WARN_ON(!atomic_read(&sd->s_count));
-		atomic_inc(&sd->s_count);
+		if (sd->s_parent && unlikely(!sysfs_get_active(sd->s_parent)))
+			return NULL;
+		if (unlikely(!sysfs_get_active(sd))) {
+			sysfs_put_active(sd->s_parent);
+			return NULL;
+		}
 	}
 	return sd;
 }
 
-static inline void sysfs_put(struct sysfs_dirent * sd)
+/**
+ *	sysfs_put_active_two - put active references to sysfs_dirent and parent
+ *	@sd: sysfs_dirent of interest
+ *
+ *	Put active references to @sd and its parent.  This function is
+ *	noop if @sd is NULL.
+ */
+static inline void sysfs_put_active_two(struct sysfs_dirent *sd)
 {
-	if (sd && atomic_dec_and_test(&sd->s_count))
-		release_sysfs_dirent(sd);
+	if (sd) {
+		sysfs_put_active(sd);
+		sysfs_put_active(sd->s_parent);
+	}
+}
+
+/**
+ *	sysfs_deactivate - deactivate sysfs_dirent
+ *	@sd: sysfs_dirent to deactivate
+ *
+ *	Deny new active references and drain existing ones.  s_active
+ *	will be unlocked when the sysfs_dirent is released.
+ */
+static inline void sysfs_deactivate(struct sysfs_dirent *sd)
+{
+	down_write_nested(&sd->s_active, SYSFS_S_ACTIVE_DEACTIVATE);
+
+	/* s_active will be unlocked by the thread doing the final put
+	 * on @sd.  Lie to lockdep.
+	 */
+	rwsem_release(&sd->s_active.dep_map, 1, _RET_IP_);
 }
 
 static inline int sysfs_is_shadowed_inode(struct inode *inode)