linux-kernel - Re: [PATCH RFC 3/9] block, bfq: handle the case when for_each

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Message-Id: <4C1444A3-8268-4F4E-99D0-76704E69C43E@linaro.org>
Date:   Fri, 10 Dec 2021 11:06:10 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     tj@...nel.org, axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH RFC 3/9] block, bfq: handle the case when
 for_each_entity() access root group



> Il giorno 27 nov 2021, alle ore 11:11, Yu Kuai <yukuai3@...wei.com> ha scritto:
> 
> Prevent null-ptr-deref after counting root group into
> 'num_groups_with_pending_reqs'.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> block/bfq-iosched.c |  2 +-
> block/bfq-wf2q.c    | 17 +++++++++++++----
> 2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 3262d062e21f..47722f931ee3 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -864,7 +864,7 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
> 	for_each_entity(entity) {
> 		struct bfq_sched_data *sd = entity->my_sched_data;
> 
> -		if (sd->next_in_service || sd->in_service_entity) {
> +		if (sd && (sd->next_in_service || sd->in_service_entity)) {

Explain with some comment this additional check.

Paolo

> 			/*
> 			 * entity is still active, because either
> 			 * next_in_service or in_service_entity is not
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 67e32481e455..6693765ff3a0 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -965,6 +965,13 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
> 	bool backshifted = false;
> 	unsigned long long min_vstart;
> 
> +	if (is_root_entity(entity))
> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
> +		goto update;
> +#else
> +		return;
> +#endif
> +
> 	/* See comments on bfq_fqq_update_budg_for_activation */
> 	if (non_blocking_wait_rq && bfq_gt(st->vtime, entity->finish)) {
> 		backshifted = true;
> @@ -999,7 +1006,10 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
> 		entity->on_st_or_in_serv = true;
> 	}
> 
> +	bfq_update_fin_time_enqueue(entity, st, backshifted);
> +
> #ifdef CONFIG_BFQ_GROUP_IOSCHED
> +update:
> 	if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
> 		struct bfq_group *bfqg =
> 			container_of(entity, struct bfq_group, entity);
> @@ -1011,8 +1021,6 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
> 		}
> 	}
> #endif
> -
> -	bfq_update_fin_time_enqueue(entity, st, backshifted);
> }
> 
> /**
> @@ -1102,7 +1110,8 @@ static void __bfq_activate_requeue_entity(struct bfq_entity *entity,
> {
> 	struct bfq_service_tree *st = bfq_entity_service_tree(entity);
> 
> -	if (sd->in_service_entity == entity || entity->tree == &st->active)
> +	if (sd && (sd->in_service_entity == entity ||
> +		   entity->tree == &st->active))
> 		 /*
> 		  * in service or already queued on the active tree,
> 		  * requeue or reposition
> @@ -1140,7 +1149,7 @@ static void bfq_activate_requeue_entity(struct bfq_entity *entity,
> 		sd = entity->sched_data;
> 		__bfq_activate_requeue_entity(entity, sd, non_blocking_wait_rq);
> 
> -		if (!bfq_update_next_in_service(sd, entity, expiration) &&
> +		if (sd && !bfq_update_next_in_service(sd, entity, expiration) &&
> 		    !requeue)
> 			break;
> 	}
> -- 
> 2.31.1
>