linux-kernel - Re: [PATCH] ARM: add BUILD_BUG_ON to check if fixmap range spans multiple pmds

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Message-ID: <YXfDdmrCynZk/QW8@shell.armlinux.org.uk>
Date:   Tue, 26 Oct 2021 09:59:34 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     quanyang.wang@...driver.com, Thomas Gleixner <tglx@...utronix.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: add BUILD_BUG_ON to check if fixmap range spans
 multiple pmds

On Sun, Oct 24, 2021 at 11:44:31PM +0200, Linus Walleij wrote:
> On Wed, Oct 20, 2021 at 7:50 AM <quanyang.wang@...driver.com> wrote:
> 
> > From: Quanyang Wang <quanyang.wang@...driver.com>
> >
> > Not only the early fixmap range, but also the fixmap range should be
> > checked if it spans multiple pmds. When enabling CONFIG_DEBUG_HIGHMEM,
> > some systems which contain up to 16 CPUs will crash.
> >
> > Signed-off-by: Quanyang Wang <quanyang.wang@...driver.com>
> 
> Looks reasonable to me.
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> 
> Please submit this patch into Russell's patch tracker.

... and has totally broken what looks like _all_ ARM kernel builds. It
can not have been tested. Maybe it's uncovered a previously unknown
problem, but causing such a wide-range regression is disappointing.
I'm going to revert this commit.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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