linux-kernel - Re: [x86] BUG: unable to handle kernel paging request at 00740060

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Message-ID: <CA+55aFx5i=vPeqx9S2WMZdqVC+g-MTczQxPa0mi84Vbs6_YF0g@mail.gmail.com>
Date:	Tue, 8 Oct 2013 12:20:26 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jakub Jelinek <jakub@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Richard Henderson <rth@...ddle.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060

On Tue, Oct 8, 2013 at 12:05 PM, Jakub Jelinek <jakub@...hat.com> wrote:
>
> If you suspect a compiler bug, can somebody please narrow it down to
> a single object file (if I've skimmed the patch right, it is just an
> optimization, where object files compiled without and with the patch
> should actually coexist fine in the same kernel), ideally to a single
> routine if possible and post a preprocessed source + gcc command line
> + version of gcc?

It is indeed just an optimization, and we could in theory switch
between the two versions on a case-by-case basis, but we don't have
any sane way to really do that.

I'll try to see if I can reproduce this on my hardware (just applying
that patch on top of my own tip) and see if I can try to narrow things
down. But I looked at the assembly for a couple of files, and it all
looked good, and I know this patch works fine for others (ie all the
normal -tip testing), so I suspect it's something specific to what
Fengguang does.

                Linus
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