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test-bdrv-drain: Test nested poll in bdrv_drain_poll_top_level()

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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>
This commit is contained in:
Kevin Wolf 2018-09-06 12:28:10 +02:00
parent 4cf077b59f
commit ecc1a5c790
1 changed files with 13 additions and 0 deletions
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13
tests/test-bdrv-drain.c
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@ -636,6 +636,17 @@ static void test_iothread_aio_cb(void *opaque, int ret)
qemu_event_set(&done_event); 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. * 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. * 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_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 /* 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, * will make sure that it has completed as far as the BDS is concerned,
* but the drain in this thread can continue immediately after * but the drain in this thread can continue immediately after