[PATCH] bfq: Fix warning in bfqq_request_over_limit()

[PATCH] bfq: Fix warning in bfqq_request_over_limit()

[Jan Kara]

People are occasionally reporting a warning bfqq_request_over_limit()
triggering reporting that BFQ's idea of cgroup hierarchy (and its depth)
does not match what generic blkcg code thinks. This can actually happen
when bfqq gets moved between BFQ groups while bfqq_request_over_limit()
is running. Make sure the code is safe against BFQ queue being moved to
a different BFQ group.

Fixes: 76f1df88bbc2 ("bfq: Limit number of requests consumed by each cgroup")
CC: stable@vger.kernel.org
Link: https://lore.kernel.org/all/CAJCQCtTw_2C7ZSz7as5Gvq=OmnDiio=HRkQekqWpKot84sQhFA@mail.gmail.com/
Reported-by: Chris Murphy <lists@colorremedies.com>
Reported-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index e47c75f1fa0f..272d48d8f326 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -569,7 +569,7 @@ static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
 	struct bfq_entity *entity = &bfqq->entity;
 	struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
 	struct bfq_entity **entities = inline_entities;
-	int depth, level;
+	int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
 	int class_idx = bfqq->ioprio_class - 1;
 	struct bfq_sched_data *sched_data;
 	unsigned long wsum;
@@ -578,15 +578,21 @@ static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
 	if (!entity->on_st_or_in_serv)
 		return false;
 
+retry:
+	spin_lock_irq(&bfqd->lock);
 	/* +1 for bfqq entity, root cgroup not included */
 	depth = bfqg_to_blkg(bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
-	if (depth > BFQ_LIMIT_INLINE_DEPTH) {
+	if (depth > alloc_depth) {
+		spin_unlock_irq(&bfqd->lock);
+		if (entities != inline_entities)
+			kfree(entities);
 		entities = kmalloc_array(depth, sizeof(*entities), GFP_NOIO);
 		if (!entities)
 			return false;
+		alloc_depth = depth;
+		goto retry;
 	}
 
-	spin_lock_irq(&bfqd->lock);
 	sched_data = entity->sched_data;
 	/* Gather our ancestors as we need to traverse them in reverse order */
 	level = 0;
-- 
2.34.1

Re: [PATCH] bfq: Fix warning in bfqq_request_over_limit()

[Jan Kara]

On Thu 07-04-22 16:07:38, Jan Kara wrote:
> People are occasionally reporting a warning bfqq_request_over_limit()
> triggering reporting that BFQ's idea of cgroup hierarchy (and its depth)
> does not match what generic blkcg code thinks. This can actually happen
> when bfqq gets moved between BFQ groups while bfqq_request_over_limit()
> is running. Make sure the code is safe against BFQ queue being moved to
> a different BFQ group.
> 
> Fixes: 76f1df88bbc2 ("bfq: Limit number of requests consumed by each cgroup")
> CC: stable@vger.kernel.org
> Link: https://lore.kernel.org/all/CAJCQCtTw_2C7ZSz7as5Gvq=OmnDiio=HRkQekqWpKot84sQhFA@mail.gmail.com/
> Reported-by: Chris Murphy <lists@colorremedies.com>
> Reported-by: "yukuai (C)" <yukuai3@huawei.com>
> Signed-off-by: Jan Kara <jack@suse.cz>

Ping guys? Can we get the fix in please? It is pretty trivial...

								Honza

> ---
>  block/bfq-iosched.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index e47c75f1fa0f..272d48d8f326 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -569,7 +569,7 @@ static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
>  	struct bfq_entity *entity = &bfqq->entity;
>  	struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
>  	struct bfq_entity **entities = inline_entities;
> -	int depth, level;
> +	int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
>  	int class_idx = bfqq->ioprio_class - 1;
>  	struct bfq_sched_data *sched_data;
>  	unsigned long wsum;
> @@ -578,15 +578,21 @@ static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
>  	if (!entity->on_st_or_in_serv)
>  		return false;
>  
> +retry:
> +	spin_lock_irq(&bfqd->lock);
>  	/* +1 for bfqq entity, root cgroup not included */
>  	depth = bfqg_to_blkg(bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
> -	if (depth > BFQ_LIMIT_INLINE_DEPTH) {
> +	if (depth > alloc_depth) {
> +		spin_unlock_irq(&bfqd->lock);
> +		if (entities != inline_entities)
> +			kfree(entities);
>  		entities = kmalloc_array(depth, sizeof(*entities), GFP_NOIO);
>  		if (!entities)
>  			return false;
> +		alloc_depth = depth;
> +		goto retry;
>  	}
>  
> -	spin_lock_irq(&bfqd->lock);
>  	sched_data = entity->sched_data;
>  	/* Gather our ancestors as we need to traverse them in reverse order */
>  	level = 0;
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] bfq: Fix warning in bfqq_request_over_limit()

[Jens Axboe]

On Thu, 7 Apr 2022 16:07:38 +0200, Jan Kara wrote:
> People are occasionally reporting a warning bfqq_request_over_limit()
> triggering reporting that BFQ's idea of cgroup hierarchy (and its depth)
> does not match what generic blkcg code thinks. This can actually happen
> when bfqq gets moved between BFQ groups while bfqq_request_over_limit()
> is running. Make sure the code is safe against BFQ queue being moved to
> a different BFQ group.
> 
> [...]

Applied, thanks!

[1/1] bfq: Fix warning in bfqq_request_over_limit()
      commit: 09df6a75fffa68169c5ef9bef990cd7ba94f3eef

Best regards,
-- 
Jens Axboe