Re: [PATCH RFC v7 11/12] smartpqi: enable host tagset

[John Garry <john.garry@huawei.com>]

On 14/07/2020 14:16, John Garry wrote:
> Hi Hannes,
> 
>>   static struct pqi_io_request *pqi_alloc_io_request(
>> -    struct pqi_ctrl_info *ctrl_info)
>> +    struct pqi_ctrl_info *ctrl_info, struct scsi_cmnd *scmd)
>>   {
>>       struct pqi_io_request *io_request;
>> +    unsigned int limit = PQI_RESERVED_IO_SLOTS;
>>       u16 i = ctrl_info->next_io_request_slot;    /* benignly racy */
>> -    while (1) {
>> +    if (scmd) {
>> +        u32 blk_tag = blk_mq_unique_tag(scmd->request);
>> +
>> +        i = blk_mq_unique_tag_to_tag(blk_tag) + limit;
>>           io_request = &ctrl_info->io_request_pool[i];
> 
> This looks ok
> 
>> -        if (atomic_inc_return(&io_request->refcount) == 1)
>> -            break;
>> -        atomic_dec(&io_request->refcount);
>> -        i = (i + 1) % ctrl_info->max_io_slots;
>> +        if (WARN_ON(atomic_inc_return(&io_request->refcount) > 1)) {
>> +            atomic_dec(&io_request->refcount);
>> +            return NULL;
>> +        }
>> +    } else {
>> +        while (1) {
>> +            io_request = &ctrl_info->io_request_pool[i];
>> +            if (atomic_inc_return(&io_request->refcount) == 1)
>> +                break;
>> +            atomic_dec(&io_request->refcount);
>> +            i = (i + 1) % limit;
> 
> To me, the range we use here looks incorrect. I would assume we should 
> restrict range to [max_io_slots - PQI_RESERVED_IO_SLOTS, max_io_slots).
> 

Sorry, I missed that you use i = blk_mq_unique_tag_to_tag(blk_tag) + 
limit for regular command.

But we still set next_io_request_slot for regular command and maybe then 
read and use it for reserved command.

Thanks