writeback: cleanup bdi_register

This patch makes sure we first initialize everything and set the BDI_registered
flag, and only after this we add the bdi to 'bdi_list'. Current code adds the
bdi to the list too early, and as a result I the

WARN(!test_bit(BDI_registered, &bdi->state)

in bdi forker is triggered. Also, it is in general good practice to make things
visible only when they are fully initialized.

Also, this patch does few micro clean-ups:
1. Removes the 'exit' label which does not do anything, just returns. This
   allows to get rid of few braces and 'ret' variable and make the code smaller.
2. If 'kthread_run()' fails, remove the error code it returns, not hard-coded
   '-ENOMEM'. Theoretically, some day 'kthread_run()' can return something
   else. Also, in case of failure it is not necessary to set 'bdi->wb.task' to
   NULL.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 11 insertions, 19 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 9008c4e207f6..0b8ee66993dd 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -511,23 +511,16 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                 const char *fmt, ...)
 {
         va_list args;
-        int ret = 0;
         struct device *dev;
 
         if (bdi->dev)   /* The driver needs to use separate queues per device */
-                goto exit;
+                return 0;
 
         va_start(args, fmt);
         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
         va_end(args);
-        if (IS_ERR(dev)) {
-                ret = PTR_ERR(dev);
-                goto exit;
-        }
-
-        spin_lock_bh(&bdi_lock);
-        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
-        spin_unlock_bh(&bdi_lock);
+        if (IS_ERR(dev))
+                return PTR_ERR(dev);
 
         bdi->dev = dev;
 
@@ -541,20 +534,19 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 
                 wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
                                                 dev_name(dev));
-                if (IS_ERR(wb->task)) {
-                        wb->task = NULL;
-                        ret = -ENOMEM;
-
-                        bdi_remove_from_list(bdi);
-                        goto exit;
-                }
+                if (IS_ERR(wb->task))
+                        return PTR_ERR(wb->task);
         }
 
         bdi_debug_register(bdi, dev_name(dev));
         set_bit(BDI_registered, &bdi->state);
+
+        spin_lock_bh(&bdi_lock);
+        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+        spin_unlock_bh(&bdi_lock);
+
         trace_writeback_bdi_register(bdi);
-exit:
-        return ret;
+        return 0;
 }
 EXPORT_SYMBOL(bdi_register);