linux-kernel - Avoid VLA in pgd_alloc kills boot on 32-bit machines was Re: -next20181010,1011 regression: thinkpad x60 (32 bit) dies during boot.

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Message-ID: <20181012181011.GA9098@amd>
Date:   Fri, 12 Oct 2018 20:10:11 +0200
From:   Pavel Machek <pavel@....cz>
To:     Ingo Molnar <mingo@...nel.org>, arnd@...db.de,
        akpm@...ux-foundation.org, luto@...nel.org,
        dave.hansen@...ux.intel.com, jroedel@...e.de,
        keescook@...omium.org, torvalds@...ux-foundation.org,
        toshi.kani@....com
Cc:     Thomas Gleixner <tglx@...utronix.de>, sfr@...b.auug.org.au,
        kernel list <linux-kernel@...r.kernel.org>, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org
Subject: Avoid VLA in pgd_alloc kills boot on 32-bit machines was Re:
 -next20181010,1011 regression: thinkpad x60 (32 bit) dies during boot.

Hi!

> > > So what came in between -next20181005 and the first bad one? kernel/sched/*
> > > being the first place to look at.
> > 
> > kernel/sched does not seem to contain anything too scary.
> > 
> > I know that -next20181005 works ok, and I know -next20181010 is
> > bad. Is there easy way to bisect using that information? I can do
> > bisect between -next and mainline, but that's a lot of patches and
> > thus not much fun :-(.
> > 
> > In the meantime, I reproduced the failure with T40p. Is there someone
> > with working x86-32 in -next?
> 
> Does latest -tip fail too? If yes then I suspect bisection would be needed.

And the winner is...

[1be3f247c2882a82279cbcf43717581ea943b692] x86/mm: Avoid VLA in
pgd_alloc()

"Kernel stack is corrupted in: pgd_alloc" panic kind of suggests this
is right commit.


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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