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Date:   Tue, 17 Aug 2021 05:37:19 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Dmitry Osipenko <digetx@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Thierry Reding <thierry.reding@gmail.com>,
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Subject: Re: [PATCH v4 2/3] mmc: block: Add mmc_bdev_to_card() helper
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On Tue, Aug 17, 2021 at 04:36:42AM +0300, Dmitry Osipenko wrote:
> +	if (bdev->bd_disk->major != MMC_BLOCK_MAJOR)
> +		return NULL;

The major is a dangerous check as we have all kinds of ways to override
it.  Please check the block device operations as they must be unique.