Re: [Xen-devel] [PATCH 2/3] xen-scsiback: One function call less in scsiback_device_action() after error detection

[Juergen Gross <jgross@xxxxxxxx>]

On 19/07/16 16:56, SF Markus Elfring wrote:
>>> @@ -606,7 +606,7 @@ static void scsiback_device_action(struct vscsibk_pend 
>>> *pending_req,
>>>     tmr = kzalloc(sizeof(struct scsiback_tmr), GFP_KERNEL);
>>>     if (!tmr) {
>>>             target_put_sess_cmd(se_cmd);
>>> -           goto err;
>>> +           goto do_resp;
>>>     }
>>
>> Hmm, I'm not convinced this is an improvement.
>>
>> I'd rather rename the new error label to "put_cmd" and get rid of the
>> braces in above if statement:
>>
>> -    if (!tmr) {
>> -            target_put_sess_cmd(se_cmd);
>> -            goto err;
>> -    }
>> +    if (!tmr)
>> +            goto put_cmd;
>>
>> and then in the error path:
>>
>> -err:
>> +put_cmd:
>> +    target_put_sess_cmd(se_cmd);
> 
> I am unsure on the relevance of this function on such a source position.
> Would it make sense to move it further down at the end?

You only want to call it in the first error case (allocation failure).

>> +free_tmr:
>>      kfree(tmr);
> 
> How do you think about to skip this function call after a memory
> allocation failure?

I think this just doesn't matter. If it were a hot path, yes. But trying
to do micro-optimizations in an error path is just not worth the effort.

I like a linear error path containing all the needed cleanups best.


Juergen

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