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From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     Pavel Machek <pavel@ucw.cz>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Naohiro Aota <Naohiro.Aota@wdc.com>,
        Christoph Hellwig <hch@lst.de>,
        Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
        Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 4.19 13/35] null_blk: Fix zone size initialization
Thread-Topic: [PATCH 4.19 13/35] null_blk: Fix zone size initialization
Thread-Index: AQHW4rJrXEheF1syA0iwzTfipJ4Neg==
Date:   Mon, 11 Jan 2021 02:46:57 +0000
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References: <20210104155703.375788488@linuxfoundation.org>
 <20210104155704.049016882@linuxfoundation.org>
 <20210106125449.GA7589@duo.ucw.cz>
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On 2021/01/06 21:55, Pavel Machek wrote:=0A=
> Hi!=0A=
> =0A=
>> commit 0ebcdd702f49aeb0ad2e2d894f8c124a0acc6e23 upstream.=0A=
>>=0A=
>> For a null_blk device with zoned mode enabled is currently initialized=
=0A=
>> with a number of zones equal to the device capacity divided by the zone=
=0A=
>> size, without considering if the device capacity is a multiple of the=0A=
>> zone size. If the zone size is not a divisor of the capacity, the zones=
=0A=
>> end up not covering the entire capacity, potentially resulting is out=0A=
>> of bounds accesses to the zone array.=0A=
>>=0A=
>> Fix this by adding one last smaller zone with a size equal to the=0A=
>> remainder of the disk capacity divided by the zone size if the capacity=
=0A=
>> is not a multiple of the zone size. For such smaller last zone, the zone=
=0A=
>> capacity is also checked so that it does not exceed the smaller zone=0A=
>> size.=0A=
> =0A=
>> --- a/drivers/block/null_blk_zoned.c=0A=
>> +++ b/drivers/block/null_blk_zoned.c=0A=
>> @@ -1,9 +1,9 @@=0A=
>>  // SPDX-License-Identifier: GPL-2.0=0A=
>>  #include <linux/vmalloc.h>=0A=
>> +#include <linux/sizes.h>=0A=
>>  #include "null_blk.h"=0A=
>>  =0A=
>> -/* zone_size in MBs to sectors. */=0A=
>> -#define ZONE_SIZE_SHIFT		11=0A=
>> +#define MB_TO_SECTS(mb) (((sector_t)mb * SZ_1M) >> SECTOR_SHIFT)=0A=
> =0A=
> This macro is quite dangerous. (mb) would help, but inline function=0A=
> would be better.=0A=
=0A=
Indeed.=0A=
=0A=
> =0A=
> =0A=
>> +	dev->nr_zones =3D dev_capacity_sects >> ilog2(dev->zone_size_sects);=
=0A=
>> +	if (dev_capacity_sects & (dev->zone_size_sects - 1))=0A=
>> +		dev->nr_zones++;=0A=
> =0A=
> Is this same as nr_zones =3D DIV_ROUND_UP(dev_capacity_sects,=0A=
> dev->zone_size_sects)? Would that be faster, more readable and robust=0A=
> against weird dev->zone_size_sects sizes?=0A=
=0A=
Yes, we can change to this to be more readable.=0A=
Will send a cleanup patch. Thanks !=0A=
=0A=
> =0A=
> Best regards,=0A=
> 								Pavel=0A=
> =0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=