compiler.h: Avoid nested statement expression in data_race()

It appears that compilers have trouble with nested statement
expressions. Therefore, remove one level of statement expression nesting
from the data_race() macro. This will help avoiding potential problems
in the future as its usage increases.

Reported-by: Borislav Petkov <bp@suse.de>
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20200520221712.GA21166@zn.tnic
Link: https://lkml.kernel.org/r/20200521142047.169334-10-elver@google.com

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7b090d2..f0bfbe8 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -264,12 +264,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  */
 #define data_race(expr)                                                        \
 ({                                                                     \
-       __kcsan_disable_current();                                      \
-       ({                                                              \
-               __unqual_scalar_typeof(({ expr; })) __v = ({ expr; });  \
-               __kcsan_enable_current();                               \
-               __v;                                                    \
+       __unqual_scalar_typeof(({ expr; })) __v = ({                    \
+               __kcsan_disable_current();                              \
+               expr;                                                   \
        });                                                             \
+       __kcsan_enable_current();                                       \
+       __v;                                                            \
 })
 
 /*