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

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Message-ID: <ZHjG8cBIdZsjhDOe@smile.fi.intel.com>
Date:   Thu, 1 Jun 2023 19:27:29 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jonas Gorski <jonas.gorski@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        linux-pci@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        linux-kernel@...r.kernel.org,
        Mickaël Salaün <mic@...ikod.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 Thu, Jun 01, 2023 at 07:25:46PM +0300, Andy Shevchenko wrote:
> On Wed, May 31, 2023 at 08:48:35PM +0200, Jonas Gorski wrote:
> > On Tue, 30 May 2023 at 23:34, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > On Fri, May 12, 2023 at 02:48:51PM -0500, Bjorn Helgaas wrote:

...

> > > Where are we at?  Are we going to ignore this because some Coverity
> > > reports are false positives?
> > 
> > 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.
> 
> Which is fine and you stumbled over the same mistake I made, that's why the
> documentation has been added to describe why the heck this macro is written
> the way it's written.
> 
> Coverity sucks.
> 
> > 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.
> 
> Obviously NAK.
> 
> > 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).

Oh my god, I mistakenly read this as bus macro, sorry for my rant,
it's simply wrong.

-- 
With Best Regards,
Andy Shevchenko