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);