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From e9a9c0b023ae0dcbb14543b74063cca931d8230f Mon Sep 17 00:00:00 2001
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From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
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Date: Thu, 9 Mar 2023 08:24:36 -0500
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Subject: [PATCH 08/12] aio-wait: switch to smp_mb__after_rmw()
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RH-Author: Emanuele Giuseppe Esposito <eesposit@redhat.com>
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RH-MergeRequest: 158: qatomic: add smp_mb__before/after_rmw()
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RH-Bugzilla: 2175660
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
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RH-Acked-by: David Hildenbrand <david@redhat.com>
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RH-Acked-by: Eric Auger <eric.auger@redhat.com>
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RH-Commit: [5/9] a90c96d148fdbec340a45dc6cedf3660d8be2aab (eesposit/qemu-kvm)
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2175660
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commit b532526a07ef3b903ead2e055fe6cc87b41057a3
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Author: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri Mar 3 11:03:52 2023 +0100
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aio-wait: switch to smp_mb__after_rmw()
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The barrier comes after an atomic increment, so it is enough to use
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smp_mb__after_rmw(); this avoids a double barrier on x86 systems.
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Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
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Reviewed-by: David Hildenbrand <david@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
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---
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include/block/aio-wait.h | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
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index dd9a7f6461..da13357bb8 100644
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--- a/include/block/aio-wait.h
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+++ b/include/block/aio-wait.h
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@@ -85,7 +85,7 @@ extern AioWait global_aio_wait;
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/* Increment wait_->num_waiters before evaluating cond. */ \
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qatomic_inc(&wait_->num_waiters); \
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/* Paired with smp_mb in aio_wait_kick(). */ \
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- smp_mb(); \
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+ smp_mb__after_rmw(); \
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if (ctx_ && in_aio_context_home_thread(ctx_)) { \
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while ((cond)) { \
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aio_poll(ctx_, true); \
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--
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2.39.1
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