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

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Message-ID: <20170228175725.GB13455@roeck-us.net>
Date:   Tue, 28 Feb 2017 09:57:25 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tobias Klauser <tklauser@...tanz.ch>
Cc:     Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
        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,
        Sandra Loosemore <sandra@...esourcery.com>
Subject: Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor
 module'

On Tue, Feb 28, 2017 at 04:53:31PM +0100, 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.
> 
> 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.
> 

I tried the following combinations of gcc and binutils:
	gcc 6.1.0; binutils 2.26.1
	gcc 6.3.0; binutils 2.25.1
	gcc 6.3.0; binutils 2.26.1
	gcc 6.3.0; binutils 2.27

I used buildroot 2017.02-rc3 to build the toolchains. All have the problem.

Another data point, confirming what you say above: I am relatively (99%)
sure that the code in question is not actually called. I added reference
counters to make sure that this is the case. Just the existence of the
LZ4 decompression code appears to be sufficient to cause the boot failure.
Weird.

I just hope this only affects nios2.

Guenter