linux-kernel - Re: [PATCH v2 2/4] ARM: amba: Fix race condition with driver

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Date:   Thu, 26 Apr 2018 10:45:49 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Russell King <linux@...linux.org.uk>,
        Adrian Salido <salidoa@...gle.com>,
        Nicolai Stange <nstange@...e.de>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Todd Kjos <tkjos@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] ARM: amba: Fix race condition with driver_override

Hi Greg,

On Thu, Apr 26, 2018 at 10:35 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Thu, Apr 26, 2018 at 09:40:08AM +0200, Geert Uytterhoeven wrote:
>> On Thu, Apr 26, 2018 at 9:04 AM, Greg Kroah-Hartman
>> <gregkh@...uxfoundation.org> wrote:
>> > On Wed, Apr 25, 2018 at 07:53:06PM +0200, Geert Uytterhoeven wrote:
>> >> On Wed, Apr 25, 2018 at 6:06 PM, Greg Kroah-Hartman
>> >> <gregkh@...uxfoundation.org> wrote:
>> >> > On Tue, Apr 10, 2018 at 03:21:44PM +0200, Geert Uytterhoeven wrote:
>> >> >> The driver_override implementation is susceptible to a race condition
>> >> >> when different threads are reading vs storing a different driver
>> >> >> override.  Add locking to avoid this race condition.
>> >> >>
>> >> >> Cfr. commits 6265539776a0810b ("driver core: platform: fix race
>> >> >> condition with driver_override") and 9561475db680f714 ("PCI: Fix race
>> >> >> condition with driver_override").
>> >> >>
>> >> >> Fixes: 3cf385713460eb2b ("ARM: 8256/1: driver coamba: add device binding path 'driver_override'")
>> >> >> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>> >> >> Reviewed-by: Todd Kjos <tkjos@...gle.com>
>> >> >> Cc: stable <stable@...r.kernel.org>
>> >>
>> >> > As this should go to stable kernels, I've fixed it up to apply without
>> >> > patch 1 as that's not a real "fix" that anyone needs...
>> >> >
>> >> > Please try to remember to put fixes first, and then "trivial" things
>> >> > later on in a series.
>> >>
>> >> I did it on purpose, as the fix is much more ugly without patch 1 applied.
>> >> Can't you just take patch 1, too? More consistency is always nice, even for
>> >> stable ;-)
>> >
>> > Consistency is nice, but when you have bug fixes that rely on "trivial"
>> > patches, it's usually not nice :(
>> >
>> > I already committed patch 2 to my tree without 1, so let's leave it
>> > as-is for now.
>>
>> Unfortunately the version you committed is buggy: the race condition
>> also covers the NULL check removed by the trivial patch you skipped,
>> so now you can get inconsistent behavior (no output or "(null)") on the
>> same running kernel version...
>>
>> Please revert and apply both. Thanks!
>
> Ugh, you are right, sorry about that.
>
> I've reverted the offending patch, and added them in the correct order
> now, I should have listened to you :)

Np, issue detected and fixed.
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds