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    Subject[tip: locking/kcsan] compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}_ONCE()
    The following commit has been merged into the locking/kcsan branch of tip:

    Commit-ID: 777f73c4e79106d45b304f6af0d31917864dbdf1
    Gitweb: https://git.kernel.org/tip/777f73c4e79106d45b304f6af0d31917864dbdf1
    Author: Marco Elver <elver@google.com>
    AuthorDate: Thu, 21 May 2020 16:20:44 +02:00
    Committer: Borislav Petkov <bp@suse.de>
    CommitterDate: Fri, 22 May 2020 15:19:53 +02:00

    compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}_ONCE()

    The volatile accesses no longer need to be wrapped in data_race()
    because compilers that emit instrumentation distinguishing volatile
    accesses are required for KCSAN.

    Consequently, the explicit kcsan_check_atomic*() are no longer required
    either since the compiler emits instrumentation distinguishing the
    volatile accesses.

    Finally, simplify __READ_ONCE_SCALAR() and remove __WRITE_ONCE_SCALAR().

    [ bp: Convert commit message to passive voice. ]

    Signed-off-by: Marco Elver <elver@google.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: Will Deacon <will@kernel.org>
    Link: https://lkml.kernel.org/r/20200521142047.169334-9-elver@google.com
    ---
    include/linux/compiler.h | 13 ++-----------
    1 file changed, 2 insertions(+), 11 deletions(-)

    diff --git a/include/linux/compiler.h b/include/linux/compiler.h
    index 17c98b2..7444f02 100644
    --- a/include/linux/compiler.h
    +++ b/include/linux/compiler.h
    @@ -228,9 +228,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,

    #define __READ_ONCE_SCALAR(x) \
    ({ \
    - typeof(x) *__xp = &(x); \
    - __unqual_scalar_typeof(x) __x = data_race(__READ_ONCE(*__xp)); \
    - kcsan_check_atomic_read(__xp, sizeof(*__xp)); \
    + __unqual_scalar_typeof(x) __x = __READ_ONCE(x); \
    smp_read_barrier_depends(); \
    (typeof(x))__x; \
    })
    @@ -246,17 +244,10 @@ do { \
    *(volatile typeof(x) *)&(x) = (val); \
    } while (0)

    -#define __WRITE_ONCE_SCALAR(x, val) \
    -do { \
    - typeof(x) *__xp = &(x); \
    - kcsan_check_atomic_write(__xp, sizeof(*__xp)); \
    - data_race(({ __WRITE_ONCE(*__xp, val); 0; })); \
    -} while (0)
    -
    #define WRITE_ONCE(x, val) \
    do { \
    compiletime_assert_rwonce_type(x); \
    - __WRITE_ONCE_SCALAR(x, val); \
    + __WRITE_ONCE(x, val); \
    } while (0)

    #ifdef CONFIG_KASAN
    \
     
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