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

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Message-ID: <20180426083542.GA31073@kroah.com>
Date:   Thu, 26 Apr 2018 10:35:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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

On Thu, Apr 26, 2018 at 09:40:08AM +0200, Geert Uytterhoeven wrote:
> Hi Greg,
> 
> 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 :)

greg k-h