The AioContext must be unlocked before calling blk_co_unref(), because
it takes the AioContext lock internally in blk_unref_bh(), which is
scheduled in the main thread. If we don't unlock, the AioContext is
locked twice and nested event loops such as in bdrv_graph_wrlock() will
deadlock.

Cc:  <qemu-stable@nongnu.org>
Fixes: https://issues.redhat.com/browse/RHEL-15965


Fixes: 0c7d204f
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20231208124352.30295-1-kwolf@redhat.com>