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authorDennis Zhou (Facebook) <dennisszhou@gmail.com>2018-09-11 21:41:28 +0300
committerJens Axboe <axboe@kernel.dk>2018-09-22 05:29:05 +0300
commit07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60 (patch)
treeefab6cd44e334f64c1a98ae1b57a6894d9130c23 /block/blk-cgroup.c
parent49f4c2dc2b5066e9211101c59cc0828e81d41614 (diff)
downloadlinux-07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60.tar.xz
blkcg: convert blkg_lookup_create to find closest blkg
There are several scenarios where blkg_lookup_create can fail. Examples include the blkcg dying, request_queue is dying, or simply being OOM. At the end of the day, most handle this by simply falling back to the q->root_blkg and calling it a day. This patch implements the notion of closest blkg. During blkg_lookup_create, if it fails to create, return the closest blkg found or the q->root_blkg. blkg_try_get_closest is introduced and used during association so a bio is always attached to a blkg. Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Dennis Zhou <dennisszhou@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-cgroup.c')
-rw-r--r--block/blk-cgroup.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index cd0d97bed83d..e9e3a955f61a 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -268,9 +268,8 @@ err_free_blkg:
* that all non-root blkg's have access to the parent blkg. This function
* should be called under RCU read lock and @q->queue_lock.
*
- * Returns pointer to the looked up or created blkg on success, ERR_PTR()
- * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
- * dead and bypassing, returns ERR_PTR(-EBUSY).
+ * Returns the blkg or the closest blkg if blkg_create fails as it walks
+ * down from root.
*/
struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
@@ -285,7 +284,7 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
* we shouldn't allow anything to go through for a bypassing queue.
*/
if (unlikely(blk_queue_bypass(q)))
- return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY);
+ return q->root_blkg;
blkg = __blkg_lookup(blkcg, q, true);
if (blkg)
@@ -293,19 +292,29 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
/*
* Create blkgs walking down from blkcg_root to @blkcg, so that all
- * non-root blkgs have access to their parents.
+ * non-root blkgs have access to their parents. Returns the closest
+ * blkg to the intended blkg should blkg_create() fail.
*/
while (true) {
struct blkcg *pos = blkcg;
struct blkcg *parent = blkcg_parent(blkcg);
-
- while (parent && !__blkg_lookup(parent, q, false)) {
+ struct blkcg_gq *ret_blkg = q->root_blkg;
+
+ while (parent) {
+ blkg = __blkg_lookup(parent, q, false);
+ if (blkg) {
+ /* remember closest blkg */
+ ret_blkg = blkg;
+ break;
+ }
pos = parent;
parent = blkcg_parent(parent);
}
blkg = blkg_create(pos, q, NULL);
- if (pos == blkcg || IS_ERR(blkg))
+ if (IS_ERR(blkg))
+ return ret_blkg;
+ if (pos == blkcg)
return blkg;
}
}