sysfs: implement sysfs_dirent active reference and immediate disconnect

[powerpc.git] / fs / sysfs / sysfs.h

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 6071766..d998e8e 100644 (file)
--- 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)