1 files changed, 18 insertions, 64 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 72e6eb96efe2..dbc66815a0fe 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -50,8 +50,6 @@ static struct timer_list sync_supers_timer;
 static int bdi_sync_supers(void *);
 static void sync_supers_timer_fn(unsigned long);
 
-static void bdi_add_default_flusher_thread(struct backing_dev_info *bdi);
-
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -331,6 +329,7 @@ static int bdi_forker_thread(void *ptr)
 	set_user_nice(current, 0);
 
 	for (;;) {
+		bool fork = false;
 		struct task_struct *task;
 		struct backing_dev_info *bdi, *tmp;
 
@@ -349,23 +348,30 @@ static int bdi_forker_thread(void *ptr)
 		 * a thread registered. If so, set that up.
 		 */
 		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+			if (!bdi_cap_writeback_dirty(bdi))
+				continue;
 			if (bdi->wb.task)
 				continue;
 			if (list_empty(&bdi->work_list) &&
 			    !bdi_has_dirty_io(bdi))
 				continue;
 
-			bdi_add_default_flusher_thread(bdi);
+			WARN(!test_bit(BDI_registered, &bdi->state),
+			     "bdi %p/%s is not registered!\n", bdi, bdi->name);
+
+			list_del_rcu(&bdi->bdi_list);
+			fork = true;
+			break;
 		}
+		spin_unlock_bh(&bdi_lock);
 
 		/* Keep working if default bdi still has things to do */
 		if (!list_empty(&me->bdi->work_list))
 			__set_current_state(TASK_RUNNING);
 
-		if (list_empty(&bdi_pending_list)) {
+		if (!fork) {
 			unsigned long wait;
 
-			spin_unlock_bh(&bdi_lock);
 			wait = msecs_to_jiffies(dirty_writeback_interval * 10);
 			if (wait)
 				schedule_timeout(wait);
@@ -378,13 +384,13 @@ static int bdi_forker_thread(void *ptr)
 		__set_current_state(TASK_RUNNING);
 
 		/*
-		 * This is our real job - check for pending entries in
-		 * bdi_pending_list, and create the threads that got added
+		 * Set the pending bit - if someone will try to unregister this
+		 * bdi - it'll wait on this bit.
 		 */
-		bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
-				 bdi_list);
-		list_del_init(&bdi->bdi_list);
-		spin_unlock_bh(&bdi_lock);
+		set_bit(BDI_pending, &bdi->state);
+
+		/* Make sure no one uses the picked bdi */
+		synchronize_rcu();
 
 		task = kthread_run(bdi_writeback_thread, &bdi->wb, "flush-%s",
 				   dev_name(bdi->dev));
@@ -397,7 +403,7 @@ static int bdi_forker_thread(void *ptr)
 			 * flush other bdi's to free memory.
 			 */
 			spin_lock_bh(&bdi_lock);
-			list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+			list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 			spin_unlock_bh(&bdi_lock);
 
 			bdi_flush_io(bdi);
@@ -408,57 +414,6 @@ static int bdi_forker_thread(void *ptr)
 	return 0;
 }
 
-static void bdi_add_to_pending(struct rcu_head *head)
-{
-	struct backing_dev_info *bdi;
-
-	bdi = container_of(head, struct backing_dev_info, rcu_head);
-	INIT_LIST_HEAD(&bdi->bdi_list);
-
-	spin_lock(&bdi_lock);
-	list_add_tail(&bdi->bdi_list, &bdi_pending_list);
-	spin_unlock(&bdi_lock);
-
-	/*
-	 * We are now on the pending list, wake up bdi_forker_task()
-	 * to finish the job and add us back to the active bdi_list
-	 */
-	wake_up_process(default_backing_dev_info.wb.task);
-}
-
-/*
- * Add the default flusher thread that gets created for any bdi
- * that has dirty data pending writeout
- */
-static void bdi_add_default_flusher_thread(struct backing_dev_info *bdi)
-{
-	if (!bdi_cap_writeback_dirty(bdi))
-		return;
-
-	if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
-		printk(KERN_ERR "bdi %p/%s is not registered!\n",
-							bdi, bdi->name);
-		return;
-	}
-
-	/*
-	 * Check with the helper whether to proceed adding a thread. Will only
-	 * abort if we two or more simultanous calls to
-	 * bdi_add_default_flusher_thread() occured, further additions will
-	 * block waiting for previous additions to finish.
-	 */
-	if (!test_and_set_bit(BDI_pending, &bdi->state)) {
-		list_del_rcu(&bdi->bdi_list);
-
-		/*
-		 * We must wait for the current RCU period to end before
-		 * moving to the pending list. So schedule that operation
-		 * from an RCU callback.
-		 */
-		call_rcu(&bdi->rcu_head, bdi_add_to_pending);
-	}
-}
-
 /*
  * Remove bdi from bdi_list, and ensure that it is no longer visible
  */
@@ -599,7 +554,6 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
 	spin_lock_init(&bdi->wb_lock);
-	INIT_RCU_HEAD(&bdi->rcu_head);
 	INIT_LIST_HEAD(&bdi->bdi_list);
 	INIT_LIST_HEAD(&bdi->work_list);