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[Qemu-devel] [PATCH 14/14] test-bdrv-drain: Test nested poll in bdrv_dra

From: Kevin Wolf
Subject: [Qemu-devel] [PATCH 14/14] test-bdrv-drain: Test nested poll in bdrv_drain_poll_top_level()
Date: Fri, 7 Sep 2018 18:15:20 +0200

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 <address@hidden>
 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 9641a20dd8..07ce5bfddc 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)
+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_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

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