On 10/17/2016 11:17 AM, Gabriel Krisman Bertazi wrote:
> James Bottomley <jejb@xxxxxxxxxxxxxxxxxx> writes:
>
>> On Thu, 2016-10-13 at 15:47 -0300, Gabriel Krisman Bertazi wrote:
>>> @@ -210,6 +219,13 @@ int scsi_execute(struct scsi_device *sdev, const
>>> unsigned char *cmd,
>>> */
>>> blk_execute_rq(req->q, NULL, req, 1);
>>>
>>> + if (scsi_sense_unit_attention(sense) && req->retries > 0) {
>>> + memset(sense, 0, SCSI_SENSE_BUFFERSIZE);
>>> + retries = req->retries - 1;
>>> + blk_put_request(req);
>>> + goto retry;
>>> + }
>>
>> OK, so this is more theory, but I think you can actually reuse the same
>> request to go around this loop without doing a get/put. I've cc'd Jens
>> to confirm, since no other driver I can find does this, but if it's
>> legal, it saves freeing and reallocating the request. You can then
>> replace the goto with a do { } while (...) which makes the loop obvious
>> to the next person looking at this.
>
> Hi James,
>
> I don't think the block layer currently has the machinery to reuse the
> request. I think it would be easy to add for the MQ case but I
> don't know about SQ. If we don't clean up or reinit the request before
> re-sending, we'll hit the BUG_ON in blk_start_request:
>
> BUG_ON(test_bit(REQ_ATOM_COMPLETE, &req->atomic_flags));
>
> Do you wanna take a v3 of the patch and fix this on a future patch, or
> should I be looking into patching the block layer interface? I'll be
> looking into it, but I need to get familiar with the SQ code first.
Would it make more sense to try to stick this retry logic in scsi_error.c
in check_sense? Or do we not have enough information there to decide whether
or not to retry 06/29?
-Brian
--
Brian King
Power Linux I/O
IBM Linux Technology Center
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