bdi: Use might_alloc()

Now that my little helper has landed, use it more. On top of the
existing check this also uses lockdep through the fs_reclaim
annotations.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
--
v2: git add everything ... oops

mm/backing-dev.c

@@ -644,7 +644,7 @@ struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 {
 	struct bdi_writeback *wb;
 
-	might_sleep_if(gfpflags_allow_blocking(gfp));
+	might_alloc(gfp);
 
 	if (!memcg_css->parent)
 		return &bdi->wb;