Revert "blkcg: allocate struct blkcg_gq outside request queue spinlock"

I inadvertently applied the v5 version of this patch, whereas
the agreed upon version was v5. Revert this one so we can apply
the right one.

This reverts commit 7fc6b87a.

block/blk-cgroup.c

@@ -165,18 +165,16 @@ struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
 EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
 
 /*
- * If gfp mask allows blocking, this function temporarily drops rcu and queue
- * locks to allocate memory.
+ * 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.
  */
 static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
-				    struct request_queue *q, gfp_t gfp,
-				    const struct blkcg_policy *pol)
+				    struct request_queue *q,
+				    struct blkcg_gq *new_blkg)
 {
-	struct blkcg_gq *blkg = NULL;
+	struct blkcg_gq *blkg;
 	struct bdi_writeback_congested *wb_congested;
 	int i, ret;
-	const bool drop_locks = gfpflags_allow_blocking(gfp);
-	bool preloaded = false;
 
 	WARN_ON_ONCE(!rcu_read_lock_held());
 	lockdep_assert_held(q->queue_lock);
@@ -187,53 +185,31 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 		goto err_free_blkg;
 	}
 
-	if (drop_locks) {
-		spin_unlock_irq(q->queue_lock);
-		rcu_read_unlock();
-	}
-
 	wb_congested = wb_congested_get_create(q->backing_dev_info,
-					       blkcg->css.id, gfp);
-	blkg = blkg_alloc(blkcg, q, gfp);
-
-	if (drop_locks) {
-		preloaded = !radix_tree_preload(gfp);
-		rcu_read_lock();
-		spin_lock_irq(q->queue_lock);
-	}
-
-	if (unlikely(!wb_congested || !blkg)) {
+					       blkcg->css.id,
+					       GFP_NOWAIT | __GFP_NOWARN);
+	if (!wb_congested) {
 		ret = -ENOMEM;
-		goto err_put;
-	}
-
-	blkg->wb_congested = wb_congested;
-
-	if (pol) {
-		WARN_ON(!drop_locks);
-
-		if (!blkcg_policy_enabled(q, pol)) {
-			ret = -EOPNOTSUPP;
-			goto err_put;
+		goto err_put_css;
 	}
 
-		/*
-		 * This could be the first entry point of blkcg implementation
-		 * and we shouldn't allow anything to go through for a bypassing
-		 * queue.
-		 */
-		if (unlikely(blk_queue_bypass(q))) {
-			ret = blk_queue_dying(q) ? -ENODEV : -EBUSY;
-			goto err_put;
+	/* allocate */
+	if (!new_blkg) {
+		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
+		if (unlikely(!new_blkg)) {
+			ret = -ENOMEM;
+			goto err_put_congested;
 		}
 	}
+	blkg = new_blkg;
+	blkg->wb_congested = wb_congested;
 
 	/* link parent */
 	if (blkcg_parent(blkcg)) {
 		blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
 		if (WARN_ON_ONCE(!blkg->parent)) {
 			ret = -ENODEV;
-			goto err_put;
+			goto err_put_congested;
 		}
 		blkg_get(blkg->parent);
 	}
@@ -260,9 +236,6 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 				pol->pd_online_fn(blkg->pd[i]);
 		}
 	}
-
-	if (preloaded)
-		radix_tree_preload_end();
 	blkg->online = true;
 	spin_unlock(&blkcg->lock);
 
@@ -273,45 +246,44 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 	blkg_put(blkg);
 	return ERR_PTR(ret);
 
-err_put:
-	if (preloaded)
-		radix_tree_preload_end();
-	if (wb_congested)
+err_put_congested:
 	wb_congested_put(wb_congested);
+err_put_css:
 	css_put(&blkcg->css);
 err_free_blkg:
-	blkg_free(blkg);
+	blkg_free(new_blkg);
 	return ERR_PTR(ret);
 }
 
 /**
- * __blkg_lookup_create - lookup blkg, try to create one if not there
+ * blkg_lookup_create - lookup blkg, try to create one if not there
  * @blkcg: blkcg of interest
  * @q: request_queue of interest
- * @gfp: gfp mask
- * @pol: blkcg policy (optional)
  *
  * Lookup blkg for the @blkcg - @q pair.  If it doesn't exist, try to
  * create one.  blkg creation is performed recursively from blkcg_root such
  * 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.
  *
- * When gfp mask allows blocking, rcu and queue locks may be dropped for
- * allocating memory. In this case, the locks will be reacquired on return.
- *
  * 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).
  */
-struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
-				      struct request_queue *q, gfp_t gfp,
-				      const struct blkcg_policy *pol)
+struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
+				    struct request_queue *q)
 {
 	struct blkcg_gq *blkg;
 
 	WARN_ON_ONCE(!rcu_read_lock_held());
 	lockdep_assert_held(q->queue_lock);
 
+	/*
+	 * This could be the first entry point of blkcg implementation and
+	 * 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);
+
 	blkg = __blkg_lookup(blkcg, q, true);
 	if (blkg)
 		return blkg;
@@ -329,35 +301,12 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
 			parent = blkcg_parent(parent);
 		}
 
-		blkg = blkg_create(pos, q, gfp, pol);
+		blkg = blkg_create(pos, q, NULL);
 		if (pos == blkcg || IS_ERR(blkg))
 			return blkg;
 	}
 }
 
-/**
- * blkg_lookup_create - lookup blkg, try to create one if not there
- *
- * Performs an initial queue bypass check and then passes control to
- * __blkg_lookup_create().
- */
-struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
-				    struct request_queue *q, gfp_t gfp,
-				    const struct blkcg_policy *pol)
-{
-	WARN_ON_ONCE(!rcu_read_lock_held());
-	lockdep_assert_held(q->queue_lock);
-
-	/*
-	 * This could be the first entry point of blkcg implementation and
-	 * 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 __blkg_lookup_create(blkcg, q, gfp, pol);
-}
-
 static void blkg_destroy(struct blkcg_gq *blkg)
 {
 	struct blkcg *blkcg = blkg->blkcg;
@@ -868,7 +817,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 	spin_lock_irq(disk->queue->queue_lock);
 
 	if (blkcg_policy_enabled(disk->queue, pol))
-		blkg = blkg_lookup_create(blkcg, disk->queue, GFP_KERNEL, pol);
+		blkg = blkg_lookup_create(blkcg, disk->queue);
 	else
 		blkg = ERR_PTR(-EOPNOTSUPP);
 
@@ -1107,15 +1056,30 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
  */
 int blkcg_init_queue(struct request_queue *q)
 {
-	struct blkcg_gq *blkg;
+	struct blkcg_gq *new_blkg, *blkg;
+	bool preloaded;
 	int ret;
 
+	new_blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
+	if (!new_blkg)
+		return -ENOMEM;
+
+	preloaded = !radix_tree_preload(GFP_KERNEL);
+
+	/*
+	 * Make sure the root blkg exists and count the existing blkgs.  As
+	 * @q is bypassing at this point, blkg_lookup_create() can't be
+	 * used.  Open code insertion.
+	 */
 	rcu_read_lock();
 	spin_lock_irq(q->queue_lock);
-	blkg = __blkg_lookup_create(&blkcg_root, q, GFP_KERNEL, NULL);
+	blkg = blkg_create(&blkcg_root, q, new_blkg);
 	spin_unlock_irq(q->queue_lock);
 	rcu_read_unlock();
 
+	if (preloaded)
+		radix_tree_preload_end();
+
 	if (IS_ERR(blkg))
 		return PTR_ERR(blkg);
 

include/linux/blk-cgroup.h

@@ -172,8 +172,7 @@ extern struct cgroup_subsys_state * const blkcg_root_css;
 struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
 				      struct request_queue *q, bool update_hint);
 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
-				    struct request_queue *q, gfp_t gfp,
-				    const struct blkcg_policy *pol);
+				    struct request_queue *q);
 int blkcg_init_queue(struct request_queue *q);
 void blkcg_drain_queue(struct request_queue *q);
 void blkcg_exit_queue(struct request_queue *q);
@@ -695,8 +694,7 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 	blkg = blkg_lookup(blkcg, q);
 	if (unlikely(!blkg)) {
 		spin_lock_irq(q->queue_lock);
-		blkg = blkg_lookup_create(blkcg, q, GFP_NOWAIT | __GFP_NOWARN,
-					  NULL);
+		blkg = blkg_lookup_create(blkcg, q);
 		if (IS_ERR(blkg))
 			blkg = NULL;
 		spin_unlock_irq(q->queue_lock);