From bbb21f907d1abbc75aa36a8adcbc5e1cfd800910 Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Thu, 4 Jun 2009 15:41:22 +0200
Subject: [PATCH 1/2] fix qemu_aio_flush

This is for all kvm-userland-rhel5 and shall fix bug #489205.

----
From: Andrea Arcangeli <aarcange@redhat.com>

qemu_aio_wait by invoking the bh or one of the aio completion
callbacks, could end up submitting new pending aio, breaking the
invariant that qemu_aio_flush returns only when no pending aio is
outstanding (possibly a problem for migration as such).

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Message-ID: <20090604134122.GV25483@random.random>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Dor Laor <dlaor@redhat.com>
Bugzilla: 504237
---
 qemu/aio.c      |    8 ++++++--
 qemu/qemu-aio.h |    7 ++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/qemu/aio.c b/qemu/aio.c
index 70d3cdc..ed30c74 100644
--- a/qemu/aio.c
+++ b/qemu/aio.c
@@ -104,11 +104,15 @@ void qemu_aio_flush(void)
     do {
         ret = 0;
 
+	/*
+	 * If there are pending emulated aio start them now so flush
+	 * will be able to return 1.
+	 */
+        qemu_aio_wait();
+
         LIST_FOREACH(node, &aio_handlers, node) {
             ret |= node->io_flush(node->opaque);
         }
-
-        qemu_aio_wait();
     } while (ret > 0);
 }
 
diff --git a/qemu/qemu-aio.h b/qemu/qemu-aio.h
index 7967829..f262344 100644
--- a/qemu/qemu-aio.h
+++ b/qemu/qemu-aio.h
@@ -24,9 +24,10 @@ typedef int (AioFlushHandler)(void *opaque);
  * outstanding AIO operations have been completed or cancelled. */
 void qemu_aio_flush(void);
 
-/* Wait for a single AIO completion to occur.  This function will until a
- * single AIO opeartion has completed.  It is intended to be used as a looping
- * primative when simulating synchronous IO based on asynchronous IO. */
+/* Wait for a single AIO completion to occur.  This function will wait
+ * until a single AIO event has completed and it will ensure something
+ * has moved before returning. This can issue new pending aio as
+ * result of executing I/O completion or bh callbacks. */
 void qemu_aio_wait(void);
 
 /* Register a file descriptor and associated callbacks.  Behaves very similarly
-- 
1.6.3.rc4.29.g8146