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    Subject[PATCH 20/20] context_tracking: Use arch_atomic_read() in __ct_state for KASAN
    Date
    From: "Paul E. McKenney" <paulmck@kernel.org>

    Context tracking's __ct_state() function can be invoked from noinstr state
    where RCU is not watching. This means that its use of atomic_read()
    causes KASAN to invoke the non-noinstr __kasan_check_read() function
    from the noinstr function __ct_state(). This is problematic because
    someone tracing the __kasan_check_read() function could get a nasty
    surprise because of RCU not watching.

    This commit therefore replaces the __ct_state() function's use of
    atomic_read() with arch_atomic_read(), which KASAN does not attempt to
    add instrumention to.

    Reported-by: kernel test robot <lkp@intel.com>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Cc: Frederic Weisbecker <frederic@kernel.org>
    Cc: Marco Elver <elver@google.com>
    Reviewed-by: Marco Elver <elver@google.com>
    ---
    include/linux/context_tracking_state.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
    index e20a74bc0597..4a4d56f77180 100644
    --- a/include/linux/context_tracking_state.h
    +++ b/include/linux/context_tracking_state.h
    @@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking);

    static __always_inline int __ct_state(void)
    {
    - return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
    + return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
    }
    #endif

    --
    2.25.1
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