blkcg: fix ref count issue with bio_blkcg using task_css

[linux-2.6-block.git] / block / bio.c

diff --git a/block/bio.c b/block/bio.c
index 81c05ee51d6ced51ac08a6a37f7727d82eedfde0..083f1c9cde0a596867768eb5436c8de1d7c3806c 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1988,13 +1988,19 @@ int bio_associate_blkcg_from_page(struct bio *bio, struct page *page)
  *
  * This function takes an extra reference of @blkcg_css which will be put
  * when @bio is released.  The caller must own @bio and is responsible for
- * synchronizing calls to this function.
+ * synchronizing calls to this function.  If @blkcg_css is NULL, a call to
+ * blkcg_get_css finds the current css from the kthread or task.
  */
 int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css)
 {
        if (unlikely(bio->bi_css))
                return -EBUSY;
-       css_get(blkcg_css);
+
+       if (blkcg_css)
+               css_get(blkcg_css);
+       else
+               blkcg_css = blkcg_get_css();
+
        bio->bi_css = blkcg_css;
        return 0;
 }