[PATCH -tip v3 00/11] Fix KCSAN for new ONCE (require Clang 11)

[Marco Elver <elver@google.com>]

This patch series is the conclusion to [1], where we determined that due
to various interactions with no_sanitize attributes and the new
{READ,WRITE}_ONCE(), KCSAN will require Clang 11 or later. Other
sanitizers are largely untouched, and only KCSAN now has a hard
dependency on Clang 11. To test, a recent Clang development version will
suffice [2]. While a little inconvenient for now, it is hoped that in
future we may be able to fix GCC and re-enable GCC support.

The patch "kcsan: Restrict supported compilers" contains a detailed list
of requirements that led to this decision.

Most of the patches are related to KCSAN, however, the first patch also
includes an UBSAN related fix and is a dependency for the remaining
ones. The last 2 patches clean up the attributes by moving them to the
right place, and fix KASAN's way of defining __no_kasan_or_inline,
making it consistent with KCSAN.

The series has been tested by running kcsan-test several times and
completed successfully.

[1] https://lkml.kernel.org/r/CANpmjNOGFqhtDa9wWpXs2kztQsSozbwsuMO5BqqW0c0g0zGfSA@mail.gmail.com
[2] https://github.com/llvm/llvm-project

v3:
* data_race() fix for 'const' non-scalar expressions.
* Add a missing commit message.
* Add Will's Acked-by.

v2: https://lkml.kernel.org/r/20200521110854.114437-1-elver@google.com
* Remove unnecessary kcsan_check_atomic in ONCE.
* Simplify __READ_ONCE_SCALAR and remove __WRITE_ONCE_SCALAR. This
  effectively restores Will Deacon's pre-KCSAN version:
  https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/tree/include/linux/compiler.h?h=rwonce/cleanup#n202
* Introduce patch making data_race() a single statement expression in
  response to apparent issues that compilers are having with nested
  statement expressions.

Arnd Bergmann (1):
  ubsan, kcsan: don't combine sanitizer with kcov on clang

Marco Elver (10):
  kcsan: Avoid inserting __tsan_func_entry/exit if possible
  kcsan: Support distinguishing volatile accesses
  kcsan: Pass option tsan-instrument-read-before-write to Clang
  kcsan: Remove 'noinline' from __no_kcsan_or_inline
  kcsan: Restrict supported compilers
  kcsan: Update Documentation to change supported compilers
  READ_ONCE, WRITE_ONCE: Remove data_race() and unnecessary checks
  data_race: Avoid nested statement expression
  compiler.h: Move function attributes to compiler_types.h
  compiler_types.h, kasan: Use __SANITIZE_ADDRESS__ instead of
    CONFIG_KASAN to decide inlining

 Documentation/dev-tools/kcsan.rst |  9 +-----
 include/linux/compiler.h          | 54 ++++---------------------------
 include/linux/compiler_types.h    | 32 ++++++++++++++++++
 kernel/kcsan/core.c               | 43 ++++++++++++++++++++++++
 lib/Kconfig.kcsan                 | 20 +++++++++++-
 lib/Kconfig.ubsan                 | 11 +++++++
 scripts/Makefile.kcsan            | 15 ++++++++-
 7 files changed, 127 insertions(+), 57 deletions(-)

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2.26.2.761.g0e0b3e54be-goog