linux-kernel - Re: char/tpm: Less checks in tpm_ibmvtpm

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Date:   Thu, 19 Oct 2017 22:44:48 +0200
From:   SF Markus Elfring <elfring@...rs.sourceforge.net>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Michal Suchánek <msuchanek@...e.de>,
        linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Kenneth Goldman <kgold@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nayna Jain <nayna@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Peter Hüwe <PeterHuewe@....de>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: char/tpm: Less checks in tpm_ibmvtpm_probe() after error
 detection

>> If the code doing the allocation is changed in the future the single
>> cleanup can stay whereas multiple labels have to be rewritten again.
> 
> No, they don't unless you choose bad label names.  Perhaps numbered
> labels?  We don't get a lot of those in the kernel any more.  Label
> name should be based on what the label does.  Often I see bad label
> names like generic labels:
> 
> 	foo = kmalloc();
> 	if (!foo)
> 		goto out;
> 
> What is out going to do?  Another common anti-pattern is come-from
> labels:
> 
> 	foo = kmalloc();
> 	if (!foo)
> 		goto kmalloc_failed;
> 
> Obviously, we can see from the if statement that the alloc failed and
> you *just* know the next line is going to be is going to be:
> 
> 	if (invalid)
> 		goto kmalloc_failed;
> 
> Which is wrong because kmalloc didn't fail...  But if the label name is
> based on what it does then, when you add or a remove an allocation, you
> just have to edit the one thing.

Would you be interested in an update on a topic like “Source code review
around jump label usage”?
https://lkml.org/lkml/2015/12/11/378

Regards,
Markus