[PATCH 0/4] deterministic random testing

[Rasmus Villemoes]

This is a bit of a mixed bag.

The background is that I have some sort() and list_sort() rework
planned, but as part of that series I want to extend their their test
suites somewhat to make sure I don't goof up - and I want to use lots
of random list lengths with random contents to increase the chance of
somebody eventually hitting "hey, sort() is broken when the length is
3 less than a power of 2 and only the last two elements are out of
order". But when such a case is hit, it's vitally important that the
developer can reproduce the exact same test case, which means using a
deterministic sequence of random numbers.

Since Petr noticed [1] the non-determinism in test_printf in
connection with Arpitha's work on rewriting it to kunit, this prompted
me to use test_printf as a first place to apply that principle, and
get the infrastructure in place that will avoid repeating the "module
parameter/seed the rnd_state/report the seed used" boilerplate in each
module.

Shuah, assuming the kselftest_module.h changes are ok, I think it's
most natural if you carry these patches, though I'd be happy with any
other route as well.

[1] https://lore.kernel.org/lkml/20200821113710.GA26290@alley/


Rasmus Villemoes (4):
  prandom.h: add *_state variant of prandom_u32_max
  kselftest_module.h: unconditionally expand the KSTM_MODULE_GLOBALS()
    macro
  kselftest_module.h: add struct rnd_state and seed parameter
  lib/test_printf.c: use deterministic sequence of random numbers

 Documentation/dev-tools/kselftest.rst      |  2 --
 include/linux/prandom.h                    | 29 ++++++++++++++++
 lib/test_bitmap.c                          |  3 --
 lib/test_printf.c                          | 13 ++++---
 lib/test_strscpy.c                         |  2 --
 tools/testing/selftests/kselftest_module.h | 40 ++++++++++++++++++----
 6 files changed, 72 insertions(+), 17 deletions(-)

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2.23.0