blk-cgroup: don't update the blkg lookup hint in blkg_conf_prep

blkg_conf_prep just creates a new blkg structure, there is no real
need to update the lookup hint which should only be done on a
successful lookup in the I/O path.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220927065425.257876-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 94af5f3f3620bba81468983fe2613788d46b704c..6a5c849ee061bedf05aa5fe95dccfeea8b0e7b2c 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -263,14 +263,6 @@ err_free:
        return NULL;
 }
 
-static void blkg_update_hint(struct blkcg *blkcg, struct blkcg_gq *blkg)
-{
-       lockdep_assert_held(&blkg->q->queue_lock);
-
-       if (blkcg != &blkcg_root && blkg != rcu_dereference(blkcg->blkg_hint))
-               rcu_assign_pointer(blkcg->blkg_hint, blkg);
-}
-
 /*
  * If @new_blkg is %NULL, this function tries to allocate a new one as
  * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
@@ -383,7 +375,9 @@ static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
        spin_lock_irqsave(&q->queue_lock, flags);
        blkg = blkg_lookup(blkcg, q);
        if (blkg) {
-               blkg_update_hint(blkcg, blkg);
+               if (blkcg != &blkcg_root &&
+                   blkg != rcu_dereference(blkcg->blkg_hint))
+                       rcu_assign_pointer(blkcg->blkg_hint, blkg);
                goto found;
        }
 
@@ -680,10 +674,8 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
        }
 
        blkg = blkg_lookup(blkcg, q);
-       if (blkg) {
-               blkg_update_hint(blkcg, blkg);
+       if (blkg)
                goto success;
-       }
 
        /*
         * Create blkgs walking down from blkcg_root to @blkcg, so that all
@@ -727,7 +719,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 
                blkg = blkg_lookup(pos, q);
                if (blkg) {
-                       blkg_update_hint(pos, blkg);
                        blkg_free(new_blkg);
                } else {
                        blkg = blkg_create(pos, disk, new_blkg);