From c139aa60c1007429335131167a0ca181e38c5668 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 18 Nov 2015 10:13:08 +0000 Subject: [PATCH] arm64: barriers: fix smp_load_acquire to work with const arguments A newly introduced function in include/net/sock.h passes a const argument to smp_load_acquire: static inline int sk_state_load(const struct sock *sk) { return smp_load_acquire(&sk->sk_state); } This cause an allmodconfig build failure, since our underlying load-acquire implementation does not handle const types correctly: include/net/sock.h: In function 'sk_state_load': ./arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output asm volatile ("ldarb %w0, %1" \ This patch fixes the problem by reusing the trick in READ_ONCE that loads via a non-const member of an anonymous union. This has the advantage of allowing us to use smp_load_acquire on packed structures (e.g. arch_spinlock_t) as well as primitive types. Cc: Arnd Bergmann Cc: David Daney Cc: Eric Dumazet Reported-by: Arnd Bergmann Reported-by: David Daney Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/barrier.h | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index 624f9679f4b0..9622eb48f894 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -64,27 +64,31 @@ do { \ #define smp_load_acquire(p) \ ({ \ - typeof(*p) ___p1; \ + union { typeof(*p) __val; char __c[1]; } __u; \ compiletime_assert_atomic_type(*p); \ switch (sizeof(*p)) { \ case 1: \ asm volatile ("ldarb %w0, %1" \ - : "=r" (___p1) : "Q" (*p) : "memory"); \ + : "=r" (*(__u8 *)__u.__c) \ + : "Q" (*p) : "memory"); \ break; \ case 2: \ asm volatile ("ldarh %w0, %1" \ - : "=r" (___p1) : "Q" (*p) : "memory"); \ + : "=r" (*(__u16 *)__u.__c) \ + : "Q" (*p) : "memory"); \ break; \ case 4: \ asm volatile ("ldar %w0, %1" \ - : "=r" (___p1) : "Q" (*p) : "memory"); \ + : "=r" (*(__u32 *)__u.__c) \ + : "Q" (*p) : "memory"); \ break; \ case 8: \ asm volatile ("ldar %0, %1" \ - : "=r" (___p1) : "Q" (*p) : "memory"); \ + : "=r" (*(__u64 *)__u.__c) \ + : "Q" (*p) : "memory"); \ break; \ } \ - ___p1; \ + __u.__val; \ }) #define read_barrier_depends() do { } while(0) -- 2.20.1