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Date:   Tue, 1 Nov 2022 08:09:52 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc:     linux-ide@vger.kernel.org, linux-block@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v4 1/7] block: Prevent the use of REQ_FUA with read
 operations
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References: <20221031022642.352794-1-damien.lemoal@opensource.wdc.com>
 <20221031022642.352794-2-damien.lemoal@opensource.wdc.com>
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On Mon, Oct 31, 2022 at 11:26:36AM +0900, Damien Le Moal wrote:
> +	/*
> +	 * REQ_FUA does not apply to read requests because:
> +	 * - There is no way to reliably force media access for read operations
> +	 *   with a block device that does not support FUA.
> +	 * - Not all block devices support FUA for read operations (e.g. ATA
> +	 *   devices with NCQ support turned off).
> +	 */
> +	if (!op_is_write(rq->cmd_flags) && (rq->cmd_flags & REQ_FUA)) {
> +		blk_mq_end_request(rq, BLK_STS_NOTSUPP);

How could this even happen?  If we want a debug check,  I think it
should be in submit_bio and a WARN_ON_ONCE.