arm64: barriers: fix smp_load_acquire to work with const arguments
commitc139aa60c1007429335131167a0ca181e38c5668
authorWill Deacon <will.deacon@arm.com>
Wed, 18 Nov 2015 10:13:08 +0000 (18 10:13 +0000)
committerCatalin Marinas <catalin.marinas@arm.com>
Wed, 18 Nov 2015 18:06:43 +0000 (18 18:06 +0000)
treef4ab14648498f179be80c4b3091fbfc913bac074
parent0b2aa5b80bbf4d0fb5daa1fb83ff637daa12d552
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 <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>
arch/arm64/include/asm/barrier.h