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Subject: Re: [PATCH BUGFIX 5/6] block, bfq: get a ref to a group when adding
 it to a service tree
To:     Paolo Valente <paolo.valente@linaro.org>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        bfq-iosched@googlegroups.com, oleksandr@natalenko.name,
        patdung100@gmail.com, cevich@redhat.com
References: <20200131092409.10867-1-paolo.valente@linaro.org>
 <20200131092409.10867-6-paolo.valente@linaro.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <0572f01d-ab0a-b89e-a5d4-6ddf2d3db18e@kernel.dk>
Date:   Fri, 31 Jan 2020 21:44:21 -0700
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On 1/31/20 2:24 AM, Paolo Valente wrote:
> BFQ schedules generic entities, which may represent either bfq_queues
> or groups of bfq_queues. When an entity is inserted into a service
> tree, a reference must be taken, to make sure that the entity does not
> disappear while still referred in the tree. Unfortunately, such a
> reference is mistakenly taken only if the entity represents a
> bfq_queue. This commit takes a reference also in case the entity
> represents a group.
> 
> Tested-by: Chris Evich <cevich@redhat.com>
> Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
> ---
>  block/bfq-cgroup.c  |  2 +-
>  block/bfq-iosched.h |  1 +
>  block/bfq-wf2q.c    | 16 +++++++++++++++-
>  3 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index c818c64766e5..f85b25fd06f2 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -332,7 +332,7 @@ static void bfqg_put(struct bfq_group *bfqg)
>  		kfree(bfqg);
>  }
>  
> -static void bfqg_and_blkg_get(struct bfq_group *bfqg)
> +void bfqg_and_blkg_get(struct bfq_group *bfqg)
>  {
>  	/* see comments in bfq_bic_update_cgroup for why refcounting bfqg */
>  	bfqg_get(bfqg);
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index f1cb89def7f8..b9627ec7007b 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -984,6 +984,7 @@ struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
>  struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg);
>  struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
>  struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node);
> +void bfqg_and_blkg_get(struct bfq_group *bfqg);
>  void bfqg_and_blkg_put(struct bfq_group *bfqg);
>  
>  #ifdef CONFIG_BFQ_GROUP_IOSCHED
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 26776bdbdf36..ef06e0d34b5b 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -533,7 +533,13 @@ static void bfq_get_entity(struct bfq_entity *entity)
>  		bfqq->ref++;
>  		bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
>  			     bfqq, bfqq->ref);
> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
> +	} else
> +		bfqg_and_blkg_get(container_of(entity, struct bfq_group,
> +					       entity));
> +#else
>  	}
> +#endif

These are really an eyesore and needs improving. Surely that can be done
in a cleaner way?

-- 
Jens Axboe