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

[Guenter Roeck]

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.

I tried to track down the problem, with no success. Just the presence
of the LZ4 code seems to be sufficient to cause the problem; I have
no idea why that would be the case.

Please let me know if there is anything I can do to help tracking down
the problem.

Thanks,
Guenter

---
# bad: [c4f3f22eddc982d247ffe2a6690c3e4a5c46dd09] Merge tag 'linux-kselftest-4.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest
# good: [9e314890292c0dd357eadef6a043704fa0b4c157] Merge tag 'openrisc-for-linus' of git://github.com/openrisc/linux
git bisect start 'HEAD' '9e31489'
# bad: [7067739df23ffd641ca99c967830e0ed2ba39eab] Merge branch 'i2c/for-4.11' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux
git bisect bad 7067739df23ffd641ca99c967830e0ed2ba39eab
# good: [c5adae9583ef6985875532904160c6bf9f07b453] lib: add CONFIG_TEST_SORT to enable self-test of sort()
git bisect good c5adae9583ef6985875532904160c6bf9f07b453
# bad: [edccb59429657b09806146339e2b27594c1d1da0] Merge tag 'fbdev-v4.11' of git://github.com/bzolnier/linux
git bisect bad edccb59429657b09806146339e2b27594c1d1da0
# good: [72db33355c1431fefcabb06c9c25705e8226eed5] fbdev: ssd1307fb: Start to use gpiod API for reset gpio
git bisect good 72db33355c1431fefcabb06c9c25705e8226eed5
# bad: [95330473636e5e4546f94874c957c3be66bb2140] checkpatch: remove false unbalanced braces warning
git bisect bad 95330473636e5e4546f94874c957c3be66bb2140
# bad: [69c78423b8f439b077929410bdf8f88e7031b891] lib/lz4: remove back-compat wrappers
git bisect bad 69c78423b8f439b077929410bdf8f88e7031b891
# bad: [e23d54e48346e775be53b3cc25a95d65da960393] lib/decompress_unlz4: change module to work with new LZ4 module version
git bisect bad e23d54e48346e775be53b3cc25a95d65da960393
# bad: [4e1a33b105ddf201f66dcc44490c6086a25eca0b] lib: update LZ4 compressor module
git bisect bad 4e1a33b105ddf201f66dcc44490c6086a25eca0b
# good: [8893f519330bb073a49c5b4676fce4be6f1be15d] lib/test_sort.c: make it explicitly non-modular
git bisect good 8893f519330bb073a49c5b4676fce4be6f1be15d
# first bad commit: [4e1a33b105ddf201f66dcc44490c6086a25eca0b] lib: update LZ4 compressor module