arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros

Passing volatile-qualified pointers to the arm64 implementations of the
load-acquire/store-release macros results in a re-load from the stack
and a bunch of associated stack-protector churn due to the temporary
result variable inheriting the volatile semantics thanks to the use of
'typeof()'.

Define these temporary variables using 'unqual_scalar_typeof' to drop
the volatile qualifier in the case that they are scalar types.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 7d9cc5ec4971da27ab6f2a3e060d15eed43761d1..fb4c27506ef411b7b77bb877d8bcf638c1ce08dd 100644 (file)
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -76,8 +76,8 @@ static inline unsigned long array_index_mask_nospec(unsigned long idx,
 #define __smp_store_release(p, v)                                      \
 do {                                                                   \
        typeof(p) __p = (p);                                            \
-       union { typeof(*p) __val; char __c[1]; } __u =                  \
-               { .__val = (__force typeof(*p)) (v) };                  \
+       union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u =  \
+               { .__val = (__force __unqual_scalar_typeof(*p)) (v) };  \
        compiletime_assert_atomic_type(*p);                             \
        kasan_check_write(__p, sizeof(*p));                             \
        switch (sizeof(*p)) {                                           \
@@ -110,7 +110,7 @@ do {                                                                        \
 
 #define __smp_load_acquire(p)                                          \
 ({                                                                     \
-       union { typeof(*p) __val; char __c[1]; } __u;                   \
+       union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        typeof(p) __p = (p);                                            \
        compiletime_assert_atomic_type(*p);                             \
        kasan_check_read(__p, sizeof(*p));                              \
@@ -136,33 +136,33 @@ do {                                                                      \
                        : "Q" (*__p) : "memory");                       \
                break;                                                  \
        }                                                               \
-       __u.__val;                                                      \
+       (typeof(*p))__u.__val;                                          \
 })
 
 #define smp_cond_load_relaxed(ptr, cond_expr)                          \
 ({                                                                     \
        typeof(ptr) __PTR = (ptr);                                      \
-       typeof(*ptr) VAL;                                               \
+       __unqual_scalar_typeof(*ptr) VAL;                               \
        for (;;) {                                                      \
                VAL = READ_ONCE(*__PTR);                                \
                if (cond_expr)                                          \
                        break;                                          \
                __cmpwait_relaxed(__PTR, VAL);                          \
        }                                                               \
-       VAL;                                                            \
+       (typeof(*ptr))VAL;                                              \
 })
 
 #define smp_cond_load_acquire(ptr, cond_expr)                          \
 ({                                                                     \
        typeof(ptr) __PTR = (ptr);                                      \
-       typeof(*ptr) VAL;                                               \
+       __unqual_scalar_typeof(*ptr) VAL;                               \
        for (;;) {                                                      \
                VAL = smp_load_acquire(__PTR);                          \
                if (cond_expr)                                          \
                        break;                                          \
                __cmpwait_relaxed(__PTR, VAL);                          \
        }                                                               \
-       VAL;                                                            \
+       (typeof(*ptr))VAL;                                              \
 })
 
 #include <asm-generic/barrier.h>