linux-kernel - Re: [PATCH 0/7] atomics: generate atomic headers

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Date:   Mon, 4 Jun 2018 18:21:22 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Andrea Parri <parri.andrea@...il.com>
Subject: Re: [PATCH 0/7] atomics: generate atomic headers

On Tue, May 29, 2018 at 8:07 PM, Mark Rutland <mark.rutland@....com> wrote:
> This series scripts the generation of the various atomic headers, to
> ensure that the various atomic APIs remain consistent, reducing the risk
> of human error, and simplifying future rework.
>
> The series is based on my atomic API cleanup patches [1,2], and can be
> found on my atomics/generated branch [3] on kernel.org.
>
> The first three patches are preparatory rework, with patch four
> introducing the infrastructure. The final three patches migrate to
> generated headers. The scripts themselves are mostly POSIX sh (modulo
> local), without bashisms, and work in dash and bash.
>
> Per Linus request that it is possible to use git grep to inspect the
> atomic headers [3], the headers are committed (and not generated by
> kbuild). Since we now expand the fallback definitions inline, each
> *should* be easier to find with grep. Each header also has a comment at
> the top with a path to the script used to generate it.
>
> While the diff stat looks like a huge addition, the scripting comes in
> at ~800 lines in total, including the fallback definitions, so we're
> removing ~1000 lines of hand-written code. At the same time, we fill in
> gaps in the atomic_long API, and the instrumented atomic wrappers.
>
> Longer-term, I think things could be simplified if we were to rework the
> headers such that we have:
>
> * arch/*/include/asm/atomic.h providing arch_atomic_*().
>
> * include/linux/atomic-raw.h building raw_atomic_*() atop of the
>   arch_atomic_*() definitions, filling in gaps in the API. Having
>   separate arch_ and raw_ namespaces would simplify the ifdeffery.
>
> * include/linux/atomic.h building atomic_*() atop of the raw_atomic_*()
>   definitions, complete with any instrumentation. Instrumenting at this
>   level would lower the instrumentation overhead, and would not require
>   any ifdeffery as the whole raw_atomic_*() API would be available.
>
> ... I've avoided this for the time being due to the necessary churn in
> arch code.
>
> Thanks,
> Mark.

Wow! Nice work!

I can say that besides KASAN, we will need hooking into atomics for
KMSAN and KTSAN in future. Without this it would be lots of manual
work with possibility of copy-paste errors.




> [1] https://lkml.kernel.org/r/20180529154346.3168-1-mark.rutland@arm.com
> [2] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git atomics/api-cleanup
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git atomics/generated
> [4] https://lkml.kernel.org/r/CA+55aFxjU0op8QLLu0n-RjHBs7gQsLvD8jcyedgw6jeZFN7B+Q@mail.gmail.com
>
> Mark Rutland (7):
>   atomics/tty: add missing atomic_long_t * cast
>   atomics/treewide: rework ordering barriers
>   atomics: separate basic {cmp,}xchg()
>   atomics: add common header generation files
>   atomics: switch to generated fallbacks
>   atomics: switch to generated atomic-long
>   atomics: switch to generated instrumentation
>
>  MAINTAINERS                                      |    1 +
>  arch/alpha/include/asm/atomic.h                  |    8 +-
>  arch/powerpc/include/asm/atomic.h                |   17 +-
>  arch/riscv/include/asm/atomic.h                  |   17 +-
>  drivers/tty/tty_ldsem.c                          |    2 +-
>  include/asm-generic/atomic-instrumented-atomic.h | 1629 ++++++++++++++++
>  include/asm-generic/atomic-instrumented.h        |  394 +---
>  include/asm-generic/atomic-long.h                | 1150 +++++++++--
>  include/linux/atomic-fallback.h                  | 2223 ++++++++++++++++++++++
>  include/linux/atomic.h                           | 1244 +-----------
>  scripts/atomic/atomic-tbl.sh                     |  186 ++
>  scripts/atomic/atomics.tbl                       |   41 +
>  scripts/atomic/fallbacks/acquire                 |    9 +
>  scripts/atomic/fallbacks/add_negative            |   16 +
>  scripts/atomic/fallbacks/add_unless              |   16 +
>  scripts/atomic/fallbacks/andnot                  |    7 +
>  scripts/atomic/fallbacks/dec                     |    7 +
>  scripts/atomic/fallbacks/dec_and_test            |   15 +
>  scripts/atomic/fallbacks/dec_if_positive         |   15 +
>  scripts/atomic/fallbacks/dec_unless_positive     |   14 +
>  scripts/atomic/fallbacks/fence                   |   11 +
>  scripts/atomic/fallbacks/fetch_add_unless        |   23 +
>  scripts/atomic/fallbacks/inc                     |    7 +
>  scripts/atomic/fallbacks/inc_and_test            |   15 +
>  scripts/atomic/fallbacks/inc_not_zero            |   14 +
>  scripts/atomic/fallbacks/inc_unless_negative     |   14 +
>  scripts/atomic/fallbacks/read_acquire            |    7 +
>  scripts/atomic/fallbacks/release                 |    8 +
>  scripts/atomic/fallbacks/set_release             |    7 +
>  scripts/atomic/fallbacks/sub_and_test            |   16 +
>  scripts/atomic/fallbacks/try_cmpxchg             |   11 +
>  scripts/atomic/gen-atomic-fallback.sh            |  144 ++
>  scripts/atomic/gen-atomic-instrumented.sh        |  122 ++
>  scripts/atomic/gen-atomic-long.sh                |   98 +
>  34 files changed, 5671 insertions(+), 1837 deletions(-)
>  create mode 100644 include/asm-generic/atomic-instrumented-atomic.h
>  create mode 100644 include/linux/atomic-fallback.h
>  create mode 100755 scripts/atomic/atomic-tbl.sh
>  create mode 100644 scripts/atomic/atomics.tbl
>  create mode 100644 scripts/atomic/fallbacks/acquire
>  create mode 100644 scripts/atomic/fallbacks/add_negative
>  create mode 100644 scripts/atomic/fallbacks/add_unless
>  create mode 100644 scripts/atomic/fallbacks/andnot
>  create mode 100644 scripts/atomic/fallbacks/dec
>  create mode 100644 scripts/atomic/fallbacks/dec_and_test
>  create mode 100644 scripts/atomic/fallbacks/dec_if_positive
>  create mode 100644 scripts/atomic/fallbacks/dec_unless_positive
>  create mode 100644 scripts/atomic/fallbacks/fence
>  create mode 100644 scripts/atomic/fallbacks/fetch_add_unless
>  create mode 100644 scripts/atomic/fallbacks/inc
>  create mode 100644 scripts/atomic/fallbacks/inc_and_test
>  create mode 100644 scripts/atomic/fallbacks/inc_not_zero
>  create mode 100644 scripts/atomic/fallbacks/inc_unless_negative
>  create mode 100644 scripts/atomic/fallbacks/read_acquire
>  create mode 100644 scripts/atomic/fallbacks/release
>  create mode 100644 scripts/atomic/fallbacks/set_release
>  create mode 100644 scripts/atomic/fallbacks/sub_and_test
>  create mode 100644 scripts/atomic/fallbacks/try_cmpxchg
>  create mode 100755 scripts/atomic/gen-atomic-fallback.sh
>  create mode 100755 scripts/atomic/gen-atomic-instrumented.sh
>  create mode 100755 scripts/atomic/gen-atomic-long.sh
>
> --
> 2.11.0
>