linux-kernel - Re: Random panic in load

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Message-ID: <CA+55aFyHU4Gwk6ASTuOgh3eFPshkgy1s5zc4p7f01DwrYddFOw@mail.gmail.com>
Date:	Sat, 26 Jul 2014 11:28:10 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Alexei Starovoitov <ast@...nel.org>,
	Michel Dänzer <michel@...nzer.net>,
	Jakub Jelinek <jakub@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Debian GCC Maintainers <debian-gcc@...ts.debian.org>,
	Debian Kernel Team <debian-kernel@...ts.debian.org>
Subject: Re: Random panic in load_balance() with 3.16-rc

On Fri, Jul 25, 2014 at 11:29 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'm sure it's possible, but it sounds potentially complicated.

Hmm. The bugzilla entry just taught me a new gcc flag:
"-fcompare-debug". That apparently makes gcc compile things twice,
once with debugging and once without, and verify that the result is
the same.

And you can enable it for the whole kernel build with just a simple

    export GCC_COMPARE_DEBUG=1

before doing the build.

It actually results in a failure for me even on my standard small
localized kernel build, even with gcc-4.8.3. I get a compare failure
for (at least) fs/ext4/inode.c.

That's a bit worrisome. I haven't actually checked if the code
generation differs in significant ways yet..

             Linus
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