Commit 239aed5d authored Oct 22, 2020 by Gabriel Krisman Bertazi Committed by Greg Kroah-Hartman Nov 10, 2020

blk-cgroup: Pre-allocate tree node on blkg_conf_prep



[ Upstream commit f255c19b3ab46d3cad3b1b2e1036f4c926cb1d0c ]

Similarly to commit 457e490f ("blkcg: allocate struct blkcg_gq
outside request queue spinlock"), blkg_create can also trigger
occasional -ENOMEM failures at the radix insertion because any
allocation inside blkg_create has to be non-blocking, making it more
likely to fail.  This causes trouble for userspace tools trying to
configure io weights who need to deal with this condition.

This patch reduces the occurrence of -ENOMEMs on this path by preloading
the radix tree element on a GFP_KERNEL context, such that we guarantee
the later non-blocking insertion won't fail.

A similar solution exists in blkcg_init_queue for the same situation.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 6dba5182

block/blk-cgroup.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -876,6 +876,12 @@ int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
		goto fail;
		}

		if (radix_tree_preload(GFP_KERNEL)) {
		blkg_free(new_blkg);
		ret = -ENOMEM;
		goto fail;
		}

		rcu_read_lock();
		spin_lock_irq(q->queue_lock);

		@@ -883,7 +889,7 @@ int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
		if (IS_ERR(blkg)) {
		ret = PTR_ERR(blkg);
		blkg_free(new_blkg);
		goto fail_unlock;
		goto fail_preloaded;
		}

		if (blkg) {
		@@ -892,10 +898,12 @@ int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
		blkg = blkg_create(pos, q, new_blkg);
		if (unlikely(IS_ERR(blkg))) {
		ret = PTR_ERR(blkg);
		goto fail_unlock;
		goto fail_preloaded;
		}
		}

		radix_tree_preload_end();

		if (pos == blkcg)
		goto success;
		}
		@@ -905,6 +913,8 @@ int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
		ctx->body = body;
		return 0;

		fail_preloaded:
		radix_tree_preload_end();
		fail_unlock:
		spin_unlock_irq(q->queue_lock);
		rcu_read_unlock();