linux-kernel - Re: [PATCH v8 0/7] Add pci_dev_for_each

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Message-ID: <ZHe8dKb3f392MfBO@bhelgaas>
Date:   Wed, 31 May 2023 16:30:28 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jonas Gorski <jonas.gorski@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mickaël Salaün <mic@...ikod.net>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andrew Lunn <andrew@...n.ch>, sparclinux@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Gregory Clement <gregory.clement@...tlin.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Russell King <linux@...linux.org.uk>,
        linux-acpi@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        xen-devel@...ts.xenproject.org, Matt Turner <mattst88@...il.com>,
        Anatolij Gustschin <agust@...x.de>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-arm-kernel@...ts.infradead.org,
        Juergen Gross <jgross@...e.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Philippe Mathieu-Daudé <philmd@...aro.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-mips@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        linux-alpha@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Maciej W. Rozycki" <macro@...am.me.uk>
Subject: Re: [PATCH v8 0/7] Add pci_dev_for_each_resource() helper and update
 users

On Wed, May 31, 2023 at 08:48:35PM +0200, Jonas Gorski wrote:
> ...

> Looking at the code I understand where coverity is coming from:
> 
> #define __pci_dev_for_each_res0(dev, res, ...)                         \
>        for (unsigned int __b = 0;                                      \
>             res = pci_resource_n(dev, __b), __b < PCI_NUM_RESOURCES;   \
>             __b++)
> 
>  res will be assigned before __b is checked for being less than
> PCI_NUM_RESOURCES, making it point to behind the array at the end of
> the last loop iteration.
> 
> Rewriting the test expression as
> 
> __b < PCI_NUM_RESOURCES && (res = pci_resource_n(dev, __b));
> 
> should avoid the (coverity) warning by making use of lazy evaluation.
> 
> It probably makes the code slightly less performant as res will now be
> checked for being not NULL (which will always be true), but I doubt it
> will be significant (or in any hot paths).

Thanks a lot for looking into this!  I think you're right, and I think
the rewritten expression is more logical as well.  Do you want to post
a patch for it?

Bjorn