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* Fix missing memory barriers

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* Fix comments about memory ordering
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Merge tag 'for-upstream-mb' of https://gitlab.com/bonzini/qemu into staging

* Fix missing memory barriers
* Fix comments about memory ordering

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# gpg: Signature made Tue 07 Mar 2023 11:40:26 GMT
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
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* tag 'for-upstream-mb' of https://gitlab.com/bonzini/qemu:
  async: clarify usage of barriers in the polling case
  async: update documentation of the memory barriers
  physmem: add missing memory barrier
  qemu-coroutine-lock: add smp_mb__after_rmw()
  aio-wait: switch to smp_mb__after_rmw()
  edu: add smp_mb__after_rmw()
  qemu-thread-win32: cleanup, fix, document QemuEvent
  qemu-thread-posix: cleanup, fix, document QemuEvent
  qatomic: add smp_mb__before/after_rmw()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Peter Maydell 2023-03-07 17:02:06 +00:00
commit 7b0f0aa55f
9 changed files with 186 additions and 70 deletions
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17
include/qemu/atomic.h
View file

@ -245,6 +245,20 @@
#define smp_wmb() smp_mb_release()
#define smp_rmb() smp_mb_acquire()
/*
* SEQ_CST is weaker than the older __sync_* builtins and Linux
* kernel read-modify-write atomics. Provide a macro to obtain
* the same semantics.
*/
#if !defined(QEMU_SANITIZE_THREAD) && \
(defined(__i386__) || defined(__x86_64__) || defined(__s390x__))
# define smp_mb__before_rmw() signal_barrier()
# define smp_mb__after_rmw() signal_barrier()
#else
# define smp_mb__before_rmw() smp_mb()
# define smp_mb__after_rmw() smp_mb()
#endif
/* qatomic_mb_read/set semantics map Java volatile variables. They are
* less expensive on some platforms (notably POWER) than fully
* sequentially consistent operations.
@ -259,7 +273,8 @@
#if !defined(QEMU_SANITIZE_THREAD) && \
(defined(__i386__) || defined(__x86_64__) || defined(__s390x__))
/* This is more efficient than a store plus a fence. */
# define qatomic_mb_set(ptr, i) ((void)qatomic_xchg(ptr, i))
# define qatomic_mb_set(ptr, i) \
({ (void)qatomic_xchg(ptr, i); smp_mb__after_rmw(); })
#else
# define qatomic_mb_set(ptr, i) \
({ qatomic_store_release(ptr, i); smp_mb(); })