block/nfs: do not poll within a coroutine

Since the former nfs_get_allocated_file_size is now a coroutine
function, it must suspend rather than poll.  Switch BDRV_POLL_WHILE()
to a qemu_coroutine_yield() loop and schedule nfs_co_generic_bh_cb()
in place of the call to bdrv_wakeup().

Fixes: 82618d7bc341 ("block: Convert bdrv_get_allocated_file_size() to co_wrapper", 2023-02-01)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230412112606.80983-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

block/nfs.c

@@ -726,10 +726,8 @@ nfs_get_allocated_file_size_cb(int ret, struct nfs_context *nfs, void *data,
     if (task->ret < 0) {
         error_report("NFS Error: %s", nfs_get_error(nfs));
     }
-
-    /* Set task->complete before reading bs->wakeup.  */
-    qatomic_mb_set(&task->complete, 1);
-    bdrv_wakeup(task->bs);
+    replay_bh_schedule_oneshot_event(task->client->aio_context,
+                                     nfs_co_generic_bh_cb, task);
 }
 
 static int64_t coroutine_fn nfs_co_get_allocated_file_size(BlockDriverState *bs)
@@ -743,15 +741,19 @@ static int64_t coroutine_fn nfs_co_get_allocated_file_size(BlockDriverState *bs)
         return client->st_blocks * 512;
     }
 
-    task.bs = bs;
+    nfs_co_init_task(bs, &task);
     task.st = &st;
-    if (nfs_fstat_async(client->context, client->fh, nfs_get_allocated_file_size_cb,
-                        &task) != 0) {
-        return -ENOMEM;
-    }
+    WITH_QEMU_LOCK_GUARD(&client->mutex) {
+        if (nfs_fstat_async(client->context, client->fh, nfs_get_allocated_file_size_cb,
+                            &task) != 0) {
+            return -ENOMEM;
+        }
 
-    nfs_set_events(client);
-    BDRV_POLL_WHILE(bs, !task.complete);
+        nfs_set_events(client);
+    }
+    while (!task.complete) {
+        qemu_coroutine_yield();
+    }
 
     return (task.ret < 0 ? task.ret : st.st_blocks * 512);
 }