linux-kernel - Re: [PATCH] gpiolib: Fix incorrect use of find_next_zero

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Date:   Mon, 1 Oct 2018 11:37:07 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>
Cc:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Peter Korsgaard <peter.korsgaard@...co.com>,
        Peter Rosin <peda@...ntia.se>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Greg KH <gregkh@...uxfoundation.org>, kishon@...com,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald <pmeerw@...erw.net>,
        Jiri Slaby <jslaby@...e.com>, Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sebastien Bourdelin <sebastien.bourdelin@...oirfairelinux.com>,
        Lukas Wunner <lukas@...ner.de>,
        Rojhalat Ibrahim <imr@...chenk.de>,
        Russell King <rmk+kernel@...linux.org.uk>,
        ext Tony Lindgren <tony@...mide.com>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-i2c@...r.kernel.org, linux-mmc <linux-mmc@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, linux-iio@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-serial@...r.kernel.org,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Fix incorrect use of find_next_zero_bit()

On Sat, Sep 29, 2018 at 2:19 PM Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:

> Commit b17566a6b08b ("gpiolib: Implement fast processing path in
> get/set array"), already fixed to some extent with commit 5d581d7e8cdc
> ("gpiolib: Fix missing updates of bitmap index"), introduced a new mode
> of processing bitmaps where bits applicable for fast bitmap processing
> path are supposed to be skipped while iterating bits which don't apply.
> Unfortunately, find_next_zero_bit() function supposed to skip over
> those fast bits is always called with a 'start' argument equal to an
> index of last zero bit found and returns that index value again an
> again, causing an infinite loop.
>
> Fix it by incrementing the index uncoditionally before
> find_next_zero_bit() is optionally called.
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>

Patch applied with Marek's Tested-by.

Thanks to both of you for digging in and fixing this up!
Now we are in good shape for the v4.20 cycle :)

Yours,
Linus Walleij