linux-kernel - Re: [PATCH 4/4] char/tpm: Less checks in tpm_ibmvtpm

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Date:   Thu, 19 Oct 2017 14:46:55 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kernel-janitors@...r.kernel.org,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Nayna Jain <nayna@...ux.vnet.ibm.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Kenneth Goldman <kgold@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Peter Hüwe <PeterHuewe@....de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 4/4] char/tpm: Less checks in tpm_ibmvtpm_probe() after
 error detection

On Thu, 19 Oct 2017 14:36:09 +0200
SF Markus Elfring <elfring@...rs.sourceforge.net> wrote:

> >> @@ -683,13 +683,10 @@ static int tpm_ibmvtpm_probe(struct vio_dev
> >> *vio_dev, reg_crq_cleanup:
> >>  	dma_unmap_single(dev, ibmvtpm->crq_dma_handle,
> >> CRQ_RES_BUF_SIZE, DMA_BIDIRECTIONAL);
> >> -cleanup:
> >> -	if (ibmvtpm) {
> >> -		if (crq_q->crq_addr)
> >> -			free_page((unsigned long)crq_q->crq_addr);
> >> -		kfree(ibmvtpm);
> >> -	}
> >> -  
> > 
> > I think a single cleanup section is better than many labels that
> > just avoid a single null check.  
> 
> I proposed to delete two unnecessary condition checks together with
> an adjustment of jump targets.
> 

They are necessary to ensure the code works with single jump target.

The compiler is free to optimize them away and create the new jump
target implicitly. Do not do the optimization in place of the compiler.
It can do it automatically, in most cases better, and automatically
adapt it to code changes.

Thanks

Michal