Re: [PATCH v2 1/1] null_blk: synchronization fix for zoned device

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/09/28 19:12, Damien Le Moal wrote:
> On 2020/09/28 18:59, Kanchan Joshi wrote:
>> Parallel write,read,zone-mgmt operations accessing/altering zone state
>> and write-pointer may get into race. Avoid the situation by using a new
>> spinlock for zoned device.
>> Concurrent zone-appends (on a zone) returning same write-pointer issue
>> is also avoided using this lock.
>>
>> Fixes: e0489ed5daeb ("null_blk: Support REQ_OP_ZONE_APPEND")
>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>> ---
>>  drivers/block/null_blk.h       |  1 +
>>  drivers/block/null_blk_zoned.c | 22 ++++++++++++++++++----
>>  2 files changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
>> index daed4a9c3436..28099be50395 100644
>> --- a/drivers/block/null_blk.h
>> +++ b/drivers/block/null_blk.h
>> @@ -44,6 +44,7 @@ struct nullb_device {
>>  	unsigned int nr_zones;
>>  	struct blk_zone *zones;
>>  	sector_t zone_size_sects;
>> +	spinlock_t zone_lock;
>>  
>>  	unsigned long size; /* device size in MB */
>>  	unsigned long completion_nsec; /* time in ns to complete a request */
>> diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
>> index 3d25c9ad2383..e8d8b13aaa5a 100644
>> --- a/drivers/block/null_blk_zoned.c
>> +++ b/drivers/block/null_blk_zoned.c
>> @@ -45,6 +45,7 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
>>  	if (!dev->zones)
>>  		return -ENOMEM;
>>  
>> +	spin_lock_init(&dev->zone_lock);
>>  	if (dev->zone_nr_conv >= dev->nr_zones) {
>>  		dev->zone_nr_conv = dev->nr_zones - 1;
>>  		pr_info("changed the number of conventional zones to %u",
>> @@ -131,8 +132,11 @@ int null_report_zones(struct gendisk *disk, sector_t sector,
>>  		 * So use a local copy to avoid corruption of the device zone
>>  		 * array.
>>  		 */
>> +		spin_lock_irq(&dev->zone_lock);
>>  		memcpy(&zone, &dev->zones[first_zone + i],
>>  		       sizeof(struct blk_zone));
>> +		spin_unlock_irq(&dev->zone_lock);
>> +
>>  		error = cb(&zone, i, data);
>>  		if (error)
>>  			return error;
>> @@ -277,18 +281,28 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
>>  blk_status_t null_process_zoned_cmd(struct nullb_cmd *cmd, enum req_opf op,
>>  				    sector_t sector, sector_t nr_sectors)
>>  {
>> +	blk_status_t sts;
>> +	struct nullb_device *dev = cmd->nq->dev;
>> +
>> +	spin_lock_irq(&dev->zone_lock);
>>  	switch (op) {
>>  	case REQ_OP_WRITE:
>> -		return null_zone_write(cmd, sector, nr_sectors, false);
>> +		sts = null_zone_write(cmd, sector, nr_sectors, false);
>> +		break;
>>  	case REQ_OP_ZONE_APPEND:
>> -		return null_zone_write(cmd, sector, nr_sectors, true);
>> +		sts = null_zone_write(cmd, sector, nr_sectors, true);
>> +		break;
>>  	case REQ_OP_ZONE_RESET:
>>  	case REQ_OP_ZONE_RESET_ALL:
>>  	case REQ_OP_ZONE_OPEN:
>>  	case REQ_OP_ZONE_CLOSE:
>>  	case REQ_OP_ZONE_FINISH:
>> -		return null_zone_mgmt(cmd, op, sector);
>> +		sts = null_zone_mgmt(cmd, op, sector);
>> +		break;
>>  	default:
>> -		return null_process_cmd(cmd, op, sector, nr_sectors);
>> +		sts = null_process_cmd(cmd, op, sector, nr_sectors);
>>  	}
>> +	spin_unlock_irq(&dev->zone_lock);
>> +
>> +	return sts;
>>  }
>>
> 
> Looks good.
> 
> Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>

Jens,

Could you queue this patch for rc2 please ?
We are seeing some issues with zone append in btrfs testing without it.


-- 
Damien Le Moal
Western Digital Research