From 8c657cb165e931b4eb6f3675495240437b0c1cb1 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 14 Sep 2018 10:55:38 +0200
Subject: [PATCH 47/49] test-bdrv-drain: Test nested poll in
 bdrv_drain_poll_top_level()

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20180914105540.18077-41-kwolf@redhat.com>
Patchwork-id: 82189
O-Subject: [RHV-7.6 qemu-kvm-rhev PATCH 40/42] test-bdrv-drain: Test nested poll in bdrv_drain_poll_top_level()
Bugzilla: 1601212
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Fam Zheng <famz@redhat.com>

This is a regression test for a deadlock that could occur in callbacks
called from the aio_poll() in bdrv_drain_poll_top_level(). The
AioContext lock wasn't released and therefore would be taken a second
time in the callback. This would cause a possible AIO_WAIT_WHILE() in
the callback to hang.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 tests/test-bdrv-drain.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tests/test-bdrv-drain.c b/tests/test-bdrv-drain.c
index 05f3b55..f4b57f7 100644
--- a/tests/test-bdrv-drain.c
+++ b/tests/test-bdrv-drain.c
@@ -636,6 +636,17 @@ static void test_iothread_aio_cb(void *opaque, int ret)
     qemu_event_set(&done_event);
 }
 
+static void test_iothread_main_thread_bh(void *opaque)
+{
+    struct test_iothread_data *data = opaque;
+
+    /* Test that the AioContext is not yet locked in a random BH that is
+     * executed during drain, otherwise this would deadlock. */
+    aio_context_acquire(bdrv_get_aio_context(data->bs));
+    bdrv_flush(data->bs);
+    aio_context_release(bdrv_get_aio_context(data->bs));
+}
+
 /*
  * Starts an AIO request on a BDS that runs in the AioContext of iothread 1.
  * The request involves a BH on iothread 2 before it can complete.
@@ -705,6 +716,8 @@ static void test_iothread_common(enum drain_type drain_type, int drain_thread)
             aio_context_acquire(ctx_a);
         }
 
+        aio_bh_schedule_oneshot(ctx_a, test_iothread_main_thread_bh, &data);
+
         /* The request is running on the IOThread a. Draining its block device
          * will make sure that it has completed as far as the BDS is concerned,
          * but the drain in this thread can continue immediately after
-- 
1.8.3.1