linux-kernel - Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor module'

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Date:   Wed, 1 Mar 2017 19:58:17 +0100
From:   Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Sandra Loosemore <sandra@...esourcery.com>,
        Tobias Klauser <tklauser@...tanz.ch>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Ley Foon Tan <lftan@...era.com>,
        nios2-dev@...ts.rocketboards.org
Subject: Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor
 module'

Hi Guenter, Tobias and Sandra,

thanks for your effort here.

On Tue, Feb 28, 2017 at 10:14:13AM -0800, Guenter Roeck wrote:
> On Tue, Feb 28, 2017 at 10:53:56AM -0700, Sandra Loosemore wrote:
> > On 02/28/2017 08:53 AM, Tobias Klauser wrote:
> > >(adding Sandra Loosemore to Cc due to possible relation to gcc/binutils
> > >for nios2)
> > >
> > >On 2017-02-26 at 22:03:38 +0100, Guenter Roeck <linux@...ck-us.net> wrote:
> > >>Hi Sven,
> > >>
> > >>my qemu test for nios2 started failing with commit 4e1a33b105dd ("lib:
> > >>update LZ4 compressor module"). The test hangs early during boot before
> > >>any console output is seen. Reverting the offending patch as well as the
> > >>subsequent lz4 related patches fixes the problem. Disabling CONFIG_RD_LZ4
> > >>and with it other LZ4 options also fixes it (as does adding "return -EINVAL;"
> > >>at the top of the LZ4 decompression code). For reference, bisect log
> > >>is attached.
> > >>
> > >>I tried with buildroot toolchains using gcc 6.1.0 as well as 6.3.0
> > >>and binutils 2.26.1. Scripts used to run the tests are available at
> > >>https://github.com/groeck/linux-build-test/tree/master/rootfs/nios2.
> > >>Qemu is from qemu mainline or qemu v2.8 with nios2 patches applied.
> > >
> > >Looks like this is somehow related to gcc/binutils. Using GCC 4.8.3 and
> > >binutils 2.24.51 (both from from Sourcery CodeBench Lite 2014.05) I can
> > >get a kernel booting on latest master branch. AFAICT, none of the
> > >LZ4_decompress_* functions are called during boot.
> > >

It seems a bit strange that code which is not actually called causes problems like that.

Please let me know if and how I may help you figure out what's happening, especially
regarding the differences between the previous LZ4 and the current implementation.

> > >However, using a self-built GCC 7.0 (20161127) and binutils 2.27 I can
> > >reproduce the problem you see using the instructions Guenter provided in
> > >the reply to Sven.
> > >
> > >I'll try to dig a bit deeper from here on. Any suggestions on what to
> > >look out for wrt the differences between the gcc/binutils version are
> > >welcome of course.
> > 
> > This message doesn't give me enough context to know what is going on,
> > especially without seeing the rest of the thread.  Generally speaking,
> > Mentor recommends you use one of our stable releases instead of trying to
> > roll your own from mainline sources.  As an upstream binutils and gcc
> > maintainer I do try my best to look at bug reports for those components, but
> > I need a reproducible standalone testcase and specific versions of the
> > different components involved.
> > 
> The problem is also seen with Sourcery CodeBench Lite 2016.11-32 (gcc 6.2.0,
> binutils 2.26.51). I can provide additional details if needed, but we don't
> have a well enough understanding of the problem to be able to provide a
> reduced size test case. The test used to reproduce the problem is available
> at https://github.com/groeck/linux-build-test/tree/master/rootfs/nios2,
> run on the ToT linux kernel.
> 
> Guenter

Regards,

Sven