linux-kernel - Re: [PATCH 2/3] xen-scsiback: One function call less in scsiback_device

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Date:	Wed, 20 Jul 2016 06:35:40 +0200
From:	Juergen Gross <jgross@...e.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	xen-devel@...ts.xenproject.org, linux-scsi@...r.kernel.org,
	David Vrabel <david.vrabel@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 2/3] xen-scsiback: One function call less in
 scsiback_device_action() after error detection

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