From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 3 Mar 2023 10:03:52 +0000 (+0100)
Subject: aio-wait: switch to smp_mb__after_rmw()
X-Git-Tag: v8.0.0-rc0~21^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b532526a07ef3b903ead2e055fe6cc87b41057a3;p=thirdparty%2Fqemu.git

aio-wait: switch to smp_mb__after_rmw()

The barrier comes after an atomic increment, so it is enough to use
smp_mb__after_rmw(); this avoids a double barrier on x86 systems.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index dd9a7f6461e..da13357bb8c 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -85,7 +85,7 @@ extern AioWait global_aio_wait;
     /* Increment wait_->num_waiters before evaluating cond. */     \
     qatomic_inc(&wait_->num_waiters);                              \
     /* Paired with smp_mb in aio_wait_kick(). */                   \
-    smp_mb();                                                      \
+    smp_mb__after_rmw();                                           \
     if (ctx_ && in_aio_context_home_thread(ctx_)) {                \
         while ((cond)) {                                           \
             aio_poll(ctx_, true);                                  \