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

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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@roeck-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

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nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-02-27 00:10 +0100
  Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-02-27 21:40 +0100
  Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Sven Schmidt <4sschmid@informatik.uni-hamburg.de> - 2017-02-28 01:00 +0100
  Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Tobias Klauser <tklauser@distanz.ch> - 2017-02-28 17:10 +0100
    Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-02-28 19:00 +0100
    Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-02-28 19:20 +0100
      Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Sven Schmidt <4sschmid@informatik.uni-hamburg.de> - 2017-03-01 20:00 +0100
        Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-03-01 21:10 +0100
          Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Tobias Klauser <tklauser@distanz.ch> - 2017-03-02 17:50 +0100
            Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-03-03 04:10 +0100
              Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Tobias Klauser <tklauser@distanz.ch> - 2017-03-07 14:00 +0100
                Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-03-08 06:10 +0100
                Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-03-09 14:30 +0100
                Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Tobias Klauser <tklauser@distanz.ch> - 2017-03-09 15:50 +0100
                Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Guenter Roeck <linux@roeck-us.net> - 2017-03-09 21:10 +0100
        Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Sandra Loosemore <sandra@codesourcery.com> - 2017-03-02 02:00 +0100
          Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Tobias Klauser <tklauser@distanz.ch> - 2017-03-02 14:40 +0100
    Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor  module' Sandra Loosemore <sandra@codesourcery.com> - 2017-02-28 22:30 +0100

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