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Date:   Mon, 11 Jan 2021 09:11:46 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     leonid.ravich@dell.com
Cc:     james.smart@broadcom.com, lravich@gmail.com,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
        linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] nvmet-fc: associations list protected by rcu,
 instead of spinlock_irq where possible.
Message-ID: <20210111081146.GA27116@lst.de>
References: <20201224110542.22219-1-leonid.ravich@dell.com> <1609697575-103348-1-git-send-email-leonid.ravich@dell.com>
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In-Reply-To: <1609697575-103348-1-git-send-email-leonid.ravich@dell.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

James, can you review this patch?

On Sun, Jan 03, 2021 at 08:12:53PM +0200, leonid.ravich@dell.com wrote:
> From: Leonid Ravich <Leonid.Ravich@emc.com>
> 
> searching assoc_list protected by rcu_read_lock if list not changed inline.
> and according to the rcu list rules.
> 
> queue array embedded into nvmet_fc_tgt_assoc protected by rcu_read_lock
> according to rcu dereference/assign rules.
> 
> queue and assoc object freed after grace period by call_rcu.
> 
> tgtport lock taken for changing assoc_list.
> 
> Reviewed-by: Eldad Zinger <Eldad.Zinger@dell.com>
> Reviewed-by: Elad Grupi <Elad.Grupi@dell.com>
> Signed-off-by: Leonid Ravich <Leonid.Ravich@emc.com>
> ---
> 1) fixed sytle issus 
> 2) queues array protects by rcu as well
> 
>  drivers/nvme/target/fc.c | 81 +++++++++++++++++++++++-------------------------
>  1 file changed, 38 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
> index cd4e73a..c14c60b 100644
> --- a/drivers/nvme/target/fc.c
> +++ b/drivers/nvme/target/fc.c
> @@ -145,6 +145,7 @@ struct nvmet_fc_tgt_queue {
>  	struct list_head		avail_defer_list;
>  	struct workqueue_struct		*work_q;
>  	struct kref			ref;
> +	struct rcu_head			rcu;
>  	struct nvmet_fc_fcp_iod		fod[];		/* array of fcp_iods */
>  } __aligned(sizeof(unsigned long long));
>  
> @@ -167,6 +168,7 @@ struct nvmet_fc_tgt_assoc {
>  	struct nvmet_fc_tgt_queue	*queues[NVMET_NR_QUEUES + 1];
>  	struct kref			ref;
>  	struct work_struct		del_work;
> +	struct rcu_head			rcu;
>  };
>  
>  
> @@ -790,7 +792,6 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  			u16 qid, u16 sqsize)
>  {
>  	struct nvmet_fc_tgt_queue *queue;
> -	unsigned long flags;
>  	int ret;
>  
>  	if (qid > NVMET_NR_QUEUES)
> @@ -829,9 +830,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  		goto out_fail_iodlist;
>  
>  	WARN_ON(assoc->queues[qid]);
> -	spin_lock_irqsave(&assoc->tgtport->lock, flags);
> -	assoc->queues[qid] = queue;
> -	spin_unlock_irqrestore(&assoc->tgtport->lock, flags);
> +	rcu_assign_pointer(assoc->queues[qid], queue);
>  
>  	return queue;
>  
> @@ -851,11 +850,8 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  {
>  	struct nvmet_fc_tgt_queue *queue =
>  		container_of(ref, struct nvmet_fc_tgt_queue, ref);
> -	unsigned long flags;
>  
> -	spin_lock_irqsave(&queue->assoc->tgtport->lock, flags);
> -	queue->assoc->queues[queue->qid] = NULL;
> -	spin_unlock_irqrestore(&queue->assoc->tgtport->lock, flags);
> +	rcu_assign_pointer(queue->assoc->queues[queue->qid], NULL);
>  
>  	nvmet_fc_destroy_fcp_iodlist(queue->assoc->tgtport, queue);
>  
> @@ -863,7 +859,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  
>  	destroy_workqueue(queue->work_q);
>  
> -	kfree(queue);
> +	kfree_rcu(queue, rcu);
>  }
>  
>  static void
> @@ -965,24 +961,23 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  	struct nvmet_fc_tgt_queue *queue;
>  	u64 association_id = nvmet_fc_getassociationid(connection_id);
>  	u16 qid = nvmet_fc_getqueueid(connection_id);
> -	unsigned long flags;
>  
>  	if (qid > NVMET_NR_QUEUES)
>  		return NULL;
>  
> -	spin_lock_irqsave(&tgtport->lock, flags);
> -	list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
>  		if (association_id == assoc->association_id) {
> -			queue = assoc->queues[qid];
> +			queue = rcu_dereference(assoc->queues[qid]);
>  			if (queue &&
>  			    (!atomic_read(&queue->connected) ||
>  			     !nvmet_fc_tgt_q_get(queue)))
>  				queue = NULL;
> -			spin_unlock_irqrestore(&tgtport->lock, flags);
> +			rcu_read_unlock();
>  			return queue;
>  		}
>  	}
> -	spin_unlock_irqrestore(&tgtport->lock, flags);
> +	rcu_read_unlock();
>  	return NULL;
>  }
>  
> @@ -1137,7 +1132,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  		}
>  		if (!needrandom) {
>  			assoc->association_id = ran;
> -			list_add_tail(&assoc->a_list, &tgtport->assoc_list);
> +			list_add_tail_rcu(&assoc->a_list, &tgtport->assoc_list);
>  		}
>  		spin_unlock_irqrestore(&tgtport->lock, flags);
>  	}
> @@ -1167,7 +1162,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  
>  	nvmet_fc_free_hostport(assoc->hostport);
>  	spin_lock_irqsave(&tgtport->lock, flags);
> -	list_del(&assoc->a_list);
> +	list_del_rcu(&assoc->a_list);
>  	oldls = assoc->rcv_disconn;
>  	spin_unlock_irqrestore(&tgtport->lock, flags);
>  	/* if pending Rcv Disconnect Association LS, send rsp now */
> @@ -1177,7 +1172,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  	dev_info(tgtport->dev,
>  		"{%d:%d} Association freed\n",
>  		tgtport->fc_target_port.port_num, assoc->a_id);
> -	kfree(assoc);
> +	kfree_rcu(assoc, rcu);
>  	nvmet_fc_tgtport_put(tgtport);
>  }
>  
> @@ -1198,7 +1193,6 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  {
>  	struct nvmet_fc_tgtport *tgtport = assoc->tgtport;
>  	struct nvmet_fc_tgt_queue *queue;
> -	unsigned long flags;
>  	int i, terminating;
>  
>  	terminating = atomic_xchg(&assoc->terminating, 1);
> @@ -1207,19 +1201,23 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  	if (terminating)
>  		return;
>  
> -	spin_lock_irqsave(&tgtport->lock, flags);
> +
>  	for (i = NVMET_NR_QUEUES; i >= 0; i--) {
> -		queue = assoc->queues[i];
> -		if (queue) {
> -			if (!nvmet_fc_tgt_q_get(queue))
> -				continue;
> -			spin_unlock_irqrestore(&tgtport->lock, flags);
> -			nvmet_fc_delete_target_queue(queue);
> -			nvmet_fc_tgt_q_put(queue);
> -			spin_lock_irqsave(&tgtport->lock, flags);
> +		rcu_read_lock();
> +		queue = rcu_dereference(assoc->queues[i]);
> +		if (!queue) {
> +			rcu_read_unlock();
> +			continue;
> +		}
> +
> +		if (!nvmet_fc_tgt_q_get(queue)) {
> +			rcu_read_unlock();
> +			continue;
>  		}
> +		rcu_read_unlock();
> +		nvmet_fc_delete_target_queue(queue);
> +		nvmet_fc_tgt_q_put(queue);
>  	}
> -	spin_unlock_irqrestore(&tgtport->lock, flags);
>  
>  	dev_info(tgtport->dev,
>  		"{%d:%d} Association deleted\n",
> @@ -1234,10 +1232,9 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  {
>  	struct nvmet_fc_tgt_assoc *assoc;
>  	struct nvmet_fc_tgt_assoc *ret = NULL;
> -	unsigned long flags;
>  
> -	spin_lock_irqsave(&tgtport->lock, flags);
> -	list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
>  		if (association_id == assoc->association_id) {
>  			ret = assoc;
>  			if (!nvmet_fc_tgt_a_get(assoc))
> @@ -1245,7 +1242,7 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  			break;
>  		}
>  	}
> -	spin_unlock_irqrestore(&tgtport->lock, flags);
> +	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -1473,19 +1470,17 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  static void
>  __nvmet_fc_free_assocs(struct nvmet_fc_tgtport *tgtport)
>  {
> -	struct nvmet_fc_tgt_assoc *assoc, *next;
> -	unsigned long flags;
> +	struct nvmet_fc_tgt_assoc *assoc;
>  
> -	spin_lock_irqsave(&tgtport->lock, flags);
> -	list_for_each_entry_safe(assoc, next,
> -				&tgtport->assoc_list, a_list) {
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
>  		if (!nvmet_fc_tgt_a_get(assoc))
>  			continue;
>  		if (!schedule_work(&assoc->del_work))
>  			/* already deleting - release local reference */
>  			nvmet_fc_tgt_a_put(assoc);
>  	}
> -	spin_unlock_irqrestore(&tgtport->lock, flags);
> +	rcu_read_unlock();
>  }
>  
>  /**
> @@ -1568,16 +1563,16 @@ static void nvmet_fc_xmt_ls_rsp(struct nvmet_fc_tgtport *tgtport,
>  			continue;
>  		spin_unlock_irqrestore(&nvmet_fc_tgtlock, flags);
>  
> -		spin_lock_irqsave(&tgtport->lock, flags);
> -		list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
> -			queue = assoc->queues[0];
> +		rcu_read_lock();
> +		list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
> +			queue = rcu_dereference(assoc->queues[0]);
>  			if (queue && queue->nvme_sq.ctrl == ctrl) {
>  				if (nvmet_fc_tgt_a_get(assoc))
>  					found_ctrl = true;
>  				break;
>  			}
>  		}
> -		spin_unlock_irqrestore(&tgtport->lock, flags);
> +		rcu_read_unlock();
>  
>  		nvmet_fc_tgtport_put(tgtport);
>  
> -- 
> 1.9.3
---end quoted text---