[PATCH] arm64: barriers: fix smp_load_acquire to work with const arguments
Will Deacon
will.deacon at arm.com
Wed Nov 18 02:13:08 PST 2015
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 at arndb.de>
Cc: David Daney <david.daney at cavium.com>
Cc: Eric Dumazet <eric.dumazet at gmail.com>
Reported-by: Arnd Bergmann <arnd at arndb.de>
Reported-by: David Daney <david.daney at cavium.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
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)
--
2.1.4
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