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Date:   Mon, 7 Mar 2022 08:13:17 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        Yu Kuai <yukuai3@huawei.com>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V3 6/6] blk-mq: manage hctx map via xarray
Message-ID: <20220307071317.GC32227@lst.de>
References: <20220307064401.30056-1-ming.lei@redhat.com> <20220307064401.30056-7-ming.lei@redhat.com>
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On Mon, Mar 07, 2022 at 02:44:01PM +0800, Ming Lei wrote:
> Firstly code becomes more clean by switching to xarray from plain array.
> 
> Secondly use-after-free on q->queue_hw_ctx can be fixed because

Not a native speaker, but shouldn't this read First and Second?

>  	mutex_lock(&q->sysfs_lock);
>  	for (i = 0; i < set->nr_hw_queues; i++) {
>  		int old_node;
>  		int node = blk_mq_get_hctx_node(set, i);
> -		struct blk_mq_hw_ctx *old_hctx = hctxs[i];
> +		struct blk_mq_hw_ctx *old_hctx = xa_load(&q->hctx_table, i);

This should cand can xa_for_each_range.

>  	for (; j < end; j++) {
> -		struct blk_mq_hw_ctx *hctx = hctxs[j];
> +		struct blk_mq_hw_ctx *hctx = xa_load(&q->hctx_table, j);
>  
> -		if (hctx) {
> +		if (hctx)
>  			blk_mq_exit_hctx(q, set, hctx, j);
> -			hctxs[j] = NULL;
> -		}

Same here.