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 <arnd@arndb.de>
Cc: David Daney <david.daney@cavium.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: David Daney <david.daney@cavium.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
#define smp_load_acquire(p) \
({ \
#define smp_load_acquire(p) \
({ \
+ union { typeof(*p) __val; char __c[1]; } __u; \
compiletime_assert_atomic_type(*p); \
switch (sizeof(*p)) { \
case 1: \
asm volatile ("ldarb %w0, %1" \
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" \
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" \
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" \
break; \
case 8: \
asm volatile ("ldar %0, %1" \
- : "=r" (___p1) : "Q" (*p) : "memory"); \
+ : "=r" (*(__u64 *)__u.__c) \
+ : "Q" (*p) : "memory"); \
})
#define read_barrier_depends() do { } while(0)
})
#define read_barrier_depends() do { } while(0)