linux-kernel - Re: [RFC PATCH V3 1/1] block: reject I/O for same fd if block size changed

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Message-ID: <20210104171108.GA27235@lst.de>
Date:   Mon, 4 Jan 2021 18:11:08 +0100
From:   Christoph Hellwig <hch@....de>
To:     Minwoo Im <minwoo.im.dev@...il.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
Subject: Re: [RFC PATCH V3 1/1] block: reject I/O for same fd if block size
 changed

On Mon, Jan 04, 2021 at 10:06:59PM +0900, Minwoo Im wrote:
> +	if (q->backing_dev_info && q->backing_dev_info->owner &&
> +			limits->logical_block_size != size) {
> +		bdev = blkdev_get_no_open(q->backing_dev_info->owner->devt);
> +		bdev->bd_disk->flags |= GENHD_FL_BLOCK_SIZE_CHANGED;
> +		blkdev_put_no_open(bdev);
> +	}

We really need the backpointer from the queue to the gendisk I've wanted
to add for a while.  Can we at least restrict this to a live gendisk?

Also I think the size change flag should go into the ->state field and
use the atomic bitops helpers to avoid concurrency problems.