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Date:   Mon, 10 Oct 2022 00:39:43 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Yuwei Guan <Yuwei.Guan@zeekrlife.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blk-mq: initialize csd/fifo_time before use
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On Mon, Oct 10, 2022 at 03:19:16PM +0800, Yuwei Guan wrote:
> csd/fifo_time need to be initialized before use again,
> otherwise, it will keep the last tag value.
> 
> Signed-off-by: Yuwei Guan <Yuwei.Guan@zeekrlife.com>
> ---
>  block/blk-mq.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8070b6c10e8d..f55d41f1d150 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -383,6 +383,9 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
>         rq->end_io = NULL;
>         rq->end_io_data = NULL;
> 
> +       /* initialize csd/fifo_time before use */
> +       memset(&rq->csd, 0x0, sizeof(rq->csd));

This is a rather unusual spelling of 0.  But more importantly what
problem with reuse do you actually see here? The csd is always
initialized before use as it can't otherwise work.  fifo_time
also appears to, but the code is a bit convoluted.