linux-kernel - Re: [PATCH v3 11/11] dm-zoned: ensure only power of 2 zone sizes are allowed

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Message-ID: <20220509185432.GB18596@twin.jikos.cz>
Date:   Mon, 9 May 2022 20:54:32 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Pankaj Raghav <p.raghav@...sung.com>
Cc:     jaegeuk@...nel.org, hare@...e.de, dsterba@...e.com,
        axboe@...nel.dk, hch@....de, damien.lemoal@...nsource.wdc.com,
        snitzer@...nel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>, bvanassche@....org,
        linux-fsdevel@...r.kernel.org, matias.bjorling@....com,
        Jens Axboe <axboe@...com>, gost.dev@...sung.com,
        jonathan.derrick@...ux.dev, jiangbo.365@...edance.com,
        linux-nvme@...ts.infradead.org, dm-devel@...hat.com,
        Naohiro Aota <naohiro.aota@....com>,
        linux-kernel@...r.kernel.org, Johannes Thumshirn <jth@...nel.org>,
        Sagi Grimberg <sagi@...mberg.me>,
        Alasdair Kergon <agk@...hat.com>, linux-block@...r.kernel.org,
        Chaitanya Kulkarni <kch@...dia.com>,
        Keith Busch <kbusch@...nel.org>, linux-btrfs@...r.kernel.org,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v3 11/11] dm-zoned: ensure only power of 2 zone sizes are
 allowed

On Fri, May 06, 2022 at 10:11:05AM +0200, Pankaj Raghav wrote:
> From: Luis Chamberlain <mcgrof@...nel.org>
> 
> Today dm-zoned relies on the assumption that you have a zone size
> with a power of 2. Even though the block layer today enforces this
> requirement, these devices do exist and so provide a stop-gap measure
> to ensure these devices cannot be used by mistake
> 
> Reviewed-by: Hannes Reinecke <hare@...e.de>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  drivers/md/dm-zone.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index 3e7b1fe15..27dc4ddf2 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -231,6 +231,18 @@ static int dm_revalidate_zones(struct mapped_device *md, struct dm_table *t)
>  	struct request_queue *q = md->queue;
>  	unsigned int noio_flag;
>  	int ret;
> +	struct block_device *bdev = md->disk->part0;
> +	sector_t zone_sectors;
> +	char bname[BDEVNAME_SIZE];
> +
> +	zone_sectors = bdev_zone_sectors(bdev);
> +
> +	if (!is_power_of_2(zone_sectors)) {

is_power_of_2 takes 'unsigned long' and sector_t is u64, so this is not
32bit clean and we had an actual bug where value 1<<48 was not
recognized as power of 2.

> +		DMWARN("%s: %s only power of two zone size supported\n",
> +		       dm_device_name(md),
> +		       bdevname(bdev, bname));
> +		return 1;
> +	}
>  
>  	/*
>  	 * Check if something changed. If yes, cleanup the current resources
> -- 
> 2.25.1