Revert "sysfs, driver-core: remove unused {sysfs|device}_schedule_callback_owner()"

This reverts commit d1ba277e79889085a2faec3b68b91ce89c63f888.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 92 insertions, 0 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 28cc1acd5439..1b8b91b67fdb 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -453,3 +453,95 @@ void sysfs_remove_bin_file(struct kobject *kobj,
         kernfs_remove_by_name(kobj->sd, attr->attr.name);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
+
+struct sysfs_schedule_callback_struct {
+        struct list_head        workq_list;
+        struct kobject          *kobj;
+        void                    (*func)(void *);
+        void                    *data;
+        struct module           *owner;
+        struct work_struct      work;
+};
+
+static struct workqueue_struct *sysfs_workqueue;
+static DEFINE_MUTEX(sysfs_workq_mutex);
+static LIST_HEAD(sysfs_workq);
+static void sysfs_schedule_callback_work(struct work_struct *work)
+{
+        struct sysfs_schedule_callback_struct *ss = container_of(work,
+                        struct sysfs_schedule_callback_struct, work);
+
+        (ss->func)(ss->data);
+        kobject_put(ss->kobj);
+        module_put(ss->owner);
+        mutex_lock(&sysfs_workq_mutex);
+        list_del(&ss->workq_list);
+        mutex_unlock(&sysfs_workq_mutex);
+        kfree(ss);
+}
+
+/**
+ * sysfs_schedule_callback - helper to schedule a callback for a kobject
+ * @kobj: object we're acting for.
+ * @func: callback function to invoke later.
+ * @data: argument to pass to @func.
+ * @owner: module owning the callback code
+ *
+ * sysfs attribute methods must not unregister themselves or their parent
+ * kobject (which would amount to the same thing).  Attempts to do so will
+ * deadlock, since unregistration is mutually exclusive with driver
+ * callbacks.
+ *
+ * Instead methods can call this routine, which will attempt to allocate
+ * and schedule a workqueue request to call back @func with @data as its
+ * argument in the workqueue's process context.  @kobj will be pinned
+ * until @func returns.
+ *
+ * Returns 0 if the request was submitted, -ENOMEM if storage could not
+ * be allocated, -ENODEV if a reference to @owner isn't available,
+ * -EAGAIN if a callback has already been scheduled for @kobj.
+ */
+int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
+                void *data, struct module *owner)
+{
+        struct sysfs_schedule_callback_struct *ss, *tmp;
+
+        if (!try_module_get(owner))
+                return -ENODEV;
+
+        mutex_lock(&sysfs_workq_mutex);
+        list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
+                if (ss->kobj == kobj) {
+                        module_put(owner);
+                        mutex_unlock(&sysfs_workq_mutex);
+                        return -EAGAIN;
+                }
+        mutex_unlock(&sysfs_workq_mutex);
+
+        if (sysfs_workqueue == NULL) {
+                sysfs_workqueue = create_singlethread_workqueue("sysfsd");
+                if (sysfs_workqueue == NULL) {
+                        module_put(owner);
+                        return -ENOMEM;
+                }
+        }
+
+        ss = kmalloc(sizeof(*ss), GFP_KERNEL);
+        if (!ss) {
+                module_put(owner);
+                return -ENOMEM;
+        }
+        kobject_get(kobj);
+        ss->kobj = kobj;
+        ss->func = func;
+        ss->data = data;
+        ss->owner = owner;
+        INIT_WORK(&ss->work, sysfs_schedule_callback_work);
+        INIT_LIST_HEAD(&ss->workq_list);
+        mutex_lock(&sysfs_workq_mutex);
+        list_add_tail(&ss->workq_list, &sysfs_workq);
+        mutex_unlock(&sysfs_workq_mutex);
+        queue_work(sysfs_workqueue, &ss->work);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(sysfs_schedule_callback);