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

[Damien Le Moal]

On 2021/01/06 21:55, Pavel Machek wrote:
> 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.

Indeed.

> 
> 
>> +	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?

Yes, we can change to this to be more readable.
Will send a cleanup patch. Thanks !

> 
> Best regards,
> 								Pavel
> 


-- 
Damien Le Moal
Western Digital Research