linux-kernel - Re: [PATCH 4.19 13/35] null_blk: Fix zone size initialization

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Date:   Wed, 6 Jan 2021 13:54:49 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Naohiro Aota <naohiro.aota@....com>,
        Damien Le Moal <damien.lemoal@....com>,
        Christoph Hellwig <hch@....de>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 4.19 13/35] null_blk: Fix zone size initialization

Hi!

> commit 0ebcdd702f49aeb0ad2e2d894f8c124a0acc6e23 upstream.
> 
> For a null_blk device with zoned mode enabled is currently initialized
> with a number of zones equal to the device capacity divided by the zone
> size, without considering if the device capacity is a multiple of the
> zone size. If the zone size is not a divisor of the capacity, the zones
> end up not covering the entire capacity, potentially resulting is out
> of bounds accesses to the zone array.
> 
> Fix this by adding one last smaller zone with a size equal to the
> remainder of the disk capacity divided by the zone size if the capacity
> is not a multiple of the zone size. For such smaller last zone, the zone
> capacity is also checked so that it does not exceed the smaller zone
> size.

> --- a/drivers/block/null_blk_zoned.c
> +++ b/drivers/block/null_blk_zoned.c
> @@ -1,9 +1,9 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/vmalloc.h>
> +#include <linux/sizes.h>
>  #include "null_blk.h"
>  
> -/* zone_size in MBs to sectors. */
> -#define ZONE_SIZE_SHIFT		11
> +#define MB_TO_SECTS(mb) (((sector_t)mb * SZ_1M) >> SECTOR_SHIFT)

This macro is quite dangerous. (mb) would help, but inline function
would be better.


> +	dev->nr_zones = dev_capacity_sects >> ilog2(dev->zone_size_sects);
> +	if (dev_capacity_sects & (dev->zone_size_sects - 1))
> +		dev->nr_zones++;

Is this same as nr_zones = DIV_ROUND_UP(dev_capacity_sects,
dev->zone_size_sects)? Would that be faster, more readable and robust
against weird dev->zone_size_sects sizes?

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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