Similarly to commit 457e490f2b741 ("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.
Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
---
block/blk-cgroup.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index f9b55614d67d..bbf848604089 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -612,6 +612,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
struct gendisk *disk;
struct request_queue *q;
struct blkcg_gq *blkg;
+ bool preloaded = false;
int ret;
disk = blkcg_conf_get_disk(&input);
@@ -657,6 +658,8 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
goto fail;
}
+ preloaded = !radix_tree_preload(GFP_KERNEL);
+
rcu_read_lock();
spin_lock_irq(&q->queue_lock);
@@ -676,6 +679,9 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
}
}
+ if (preloaded)
+ radix_tree_preload_end();
+
if (pos == blkcg)
goto success;
}
@@ -688,6 +694,8 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
fail_unlock:
spin_unlock_irq(&q->queue_lock);
rcu_read_unlock();
+ if (preloaded)
+ radix_tree_preload_end();
fail:
put_disk_and_module(disk);
/*
--
2.28.0
