bdi: remove bdi->wb_lock locking around bdi->dev clearing in bdi_unregister()

The only places where NULL test on bdi->dev is used are
bdi_[un]register().  The functions can't be called in parallel anyway
and there's no point in protecting bdi->dev clearing with a lock.
Remove bdi->wb_lock grabbing around bdi->dev clearing and move it
after device_unregister() call so that bdi->dev doesn't have to be
cached in a local variable.

This patch shouldn't introduce any behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 1706cbb..4afeefe 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -402,21 +402,15 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 
 void bdi_unregister(struct backing_dev_info *bdi)
 {
-       struct device *dev = bdi->dev;
-
-       if (dev) {
+       if (bdi->dev) {
                bdi_set_min_ratio(bdi, 0);
                trace_writeback_bdi_unregister(bdi);
                bdi_prune_sb(bdi);
 
                bdi_wb_shutdown(bdi);
                bdi_debug_unregister(bdi);
-
-               spin_lock_bh(&bdi->wb_lock);
+               device_unregister(bdi->dev);
                bdi->dev = NULL;
-               spin_unlock_bh(&bdi->wb_lock);
-
-               device_unregister(dev);
        }
 }
 EXPORT_SYMBOL(bdi_unregister);