block/monitor: Fix crash when executing HMP commit

hmp_commit() calls blk_is_available() from a non-coroutine context (and
in the main loop). blk_is_available() is a co_wrapper_mixed_bdrv_rdlock
function, and in the non-coroutine context it calls AIO_WAIT_WHILE(),
which crashes if the aio_context lock is not taken before.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1615
Signed-off-by: Wang Liang <wangliangzz@inspur.com>
Message-Id: <20230424103902.45265-1-wangliangzz@126.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 8c1e8fb)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

block/monitor/block-hmp-cmds.c

@@ -214,15 +214,17 @@ void hmp_commit(Monitor *mon, const QDict *qdict)
             error_report("Device '%s' not found", device);
             return;
         }
-        if (!blk_is_available(blk)) {
-            error_report("Device '%s' has no medium", device);
-            return;
-        }
 
         bs = bdrv_skip_implicit_filters(blk_bs(blk));
         aio_context = bdrv_get_aio_context(bs);
         aio_context_acquire(aio_context);
 
+        if (!blk_is_available(blk)) {
+            error_report("Device '%s' has no medium", device);
+            aio_context_release(aio_context);
+            return;
+        }
+
         ret = bdrv_commit(bs);
 
         aio_context_release(aio_context);