Explain that aio_context_notifier_poll() relies on
aio_notify_accept() to catch all the memory writes that were
done before ctx->notified was set to true.
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
util/async.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/util/async.c b/util/async.c
index e4b494150e7d..21016a1ac7c1 100644
--- a/util/async.c
+++ b/util/async.c
@@ -474,8 +474,9 @@ void aio_notify_accept(AioContext *ctx)
qatomic_set(&ctx->notified, false);
/*
- * Write ctx->notified before reading e.g. bh->flags. Pairs with smp_wmb
- * in aio_notify.
+ * Order reads of ctx->notified (in aio_context_notifier_poll()) and the
+ * above clearing of ctx->notified before reads of e.g. bh->flags. Pairs
+ * with smp_wmb() in aio_notify.
*/
smp_mb();
}
@@ -498,6 +499,11 @@ static bool aio_context_notifier_poll(void *opaque)
EventNotifier *e = opaque;
AioContext *ctx = container_of(e, AioContext, notifier);
+ /*
+ * No need for load-acquire because we just want to kick the
+ * event loop. aio_notify_accept() takes care of synchronizing
+ * the event loop with the producers.
+ */
return qatomic_read(&ctx->notified);
}
--
2.39.1
