blk-cgroup: cleanup the blkg_lookup family of functions

Add a fully inlined blkg_lookup as the extra two checks aren't going
to generated a lot more code vs the call to the slowpath routine, and
open code the hint update in the two callers that care.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220921180501.1539876-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -263,29 +263,13 @@ err_free:
 	return NULL;
 }
 
-struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
-				      struct request_queue *q, bool update_hint)
+static void blkg_update_hint(struct blkcg *blkcg, struct blkcg_gq *blkg)
 {
-	struct blkcg_gq *blkg;
+	lockdep_assert_held(&blkg->q->queue_lock);
 
-	/*
-	 * Hint didn't match.  Look up from the radix tree.  Note that the
-	 * hint can only be updated under queue_lock as otherwise @blkg
-	 * could have already been removed from blkg_tree.  The caller is
-	 * responsible for grabbing queue_lock if @update_hint.
-	 */
-	blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
-	if (blkg && blkg->q == q) {
-		if (update_hint) {
-			lockdep_assert_held(&q->queue_lock);
-			rcu_assign_pointer(blkcg->blkg_hint, blkg);
-		}
-		return blkg;
-	}
-
-	return NULL;
+	if (blkcg != &blkcg_root && blkg != rcu_dereference(blkcg->blkg_hint))
+		rcu_assign_pointer(blkcg->blkg_hint, blkg);
 }
-EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
 
 /*
  * If @new_blkg is %NULL, this function tries to allocate a new one as
@@ -397,9 +381,11 @@ static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 		return blkg;
 
 	spin_lock_irqsave(&q->queue_lock, flags);
-	blkg = __blkg_lookup(blkcg, q, true);
-	if (blkg)
+	blkg = blkg_lookup(blkcg, q);
+	if (blkg) {
+		blkg_update_hint(blkcg, blkg);
 		goto found;
+	}
 
 	/*
 	 * Create blkgs walking down from blkcg_root to @blkcg, so that all
@@ -621,12 +607,18 @@ static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
 					  const struct blkcg_policy *pol,
 					  struct request_queue *q)
 {
+	struct blkcg_gq *blkg;
+
 	WARN_ON_ONCE(!rcu_read_lock_held());
 	lockdep_assert_held(&q->queue_lock);
 
 	if (!blkcg_policy_enabled(q, pol))
 		return ERR_PTR(-EOPNOTSUPP);
-	return __blkg_lookup(blkcg, q, true /* update_hint */);
+
+	blkg = blkg_lookup(blkcg, q);
+	if (blkg)
+		blkg_update_hint(blkcg, blkg);
+	return blkg;
 }
 
 /**

block/blk-cgroup.h

@@ -178,8 +178,6 @@ struct blkcg_policy {
 extern struct blkcg blkcg_root;
 extern bool blkcg_debug_stats;
 
-struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
-				      struct request_queue *q, bool update_hint);
 int blkcg_init_queue(struct request_queue *q);
 void blkcg_exit_queue(struct request_queue *q);
 
@@ -227,22 +225,21 @@ static inline bool bio_issue_as_root_blkg(struct bio *bio)
 }
 
 /**
- * __blkg_lookup - internal version of blkg_lookup()
+ * blkg_lookup - lookup blkg for the specified blkcg - q pair
  * @blkcg: blkcg of interest
  * @q: request_queue of interest
- * @update_hint: whether to update lookup hint with the result or not
  *
- * This is internal version and shouldn't be used by policy
- * implementations.  Looks up blkgs for the @blkcg - @q pair regardless of
- * @q's bypass state.  If @update_hint is %true, the caller should be
- * holding @q->queue_lock and lookup hint is updated on success.
+ * Lookup blkg for the @blkcg - @q pair.
+
+ * Must be called in a RCU critical section.
  */
-static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
-					     struct request_queue *q,
-					     bool update_hint)
+static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
+					   struct request_queue *q)
 {
 	struct blkcg_gq *blkg;
 
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
 	if (blkcg == &blkcg_root)
 		return q->root_blkg;
 
@@ -250,22 +247,10 @@ static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
 	if (blkg && blkg->q == q)
 		return blkg;
 
-	return blkg_lookup_slowpath(blkcg, q, update_hint);
-}
-
-/**
- * blkg_lookup - lookup blkg for the specified blkcg - q pair
- * @blkcg: blkcg of interest
- * @q: request_queue of interest
- *
- * Lookup blkg for the @blkcg - @q pair.  This function should be called
- * under RCU read lock.
- */
-static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
-					   struct request_queue *q)
-{
-	WARN_ON_ONCE(!rcu_read_lock_held());
-	return __blkg_lookup(blkcg, q, false);
+	blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
+	if (blkg && blkg->q != q)
+		blkg = NULL;
+	return blkg;
 }
 
 /**