linux-kernel - Re: Random panic in load

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Message-ID: <20140725212555.GG2397@laptop.redhat.com>
Date:	Fri, 25 Jul 2014 23:25:55 +0200
From:	Jakub Jelinek <jakub@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Michel Dänzer <michel@...nzer.net>,
	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 01:01:11PM -0700, Linus Torvalds wrote:
> For example, gcc will not create a small stack frame with "sub
> $8,%rsp". No, what gcc does is to use a random "push" instruction.
> Fair enough, but that really makes things much harder to see. Here's
> an example:

That is because for -Os, push is certainly shorter than sub $8,%rsp.

If you want to test for this gcc bug in the kernel, supposedly one should
just take the short testcase from the GCC PR, try to compile it and see if
you e.g. get a -fcompare-debug -Os failure with the testcase.
In that case, you could instead of giving up completely just
-fno-var-tracking-assignments.

	Jakub
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