DLPX-86321 Hang when zoa gets killed after object store add (openzfs#905

)

module/os/linux/zfs/vdev_object_store.c

@@ -179,6 +179,7 @@ typedef struct vdev_object_store {
 	boolean_t vos_open_completed;
 	boolean_t vos_create_completed;
 	boolean_t vos_closing;
+	boolean_t vos_synced_once;
 	const char *vos_feature_enable;
 	uint64_t vos_result;
 
@@ -1147,6 +1148,7 @@ agent_resume_state_check(vdev_t *vd)
 	    sizeof (uberblock_t)) == 0) {
 		return (0);
 	}
+
 	if (vos->vos_send_txg_selector == VOS_TXG_END) {
 		/*
 		 * In this case, it's possible that the uberblock was written
@@ -1162,6 +1164,18 @@ agent_resume_state_check(vdev_t *vd)
 			return (0);
 		}
 	}
+
+	if (!vos->vos_synced_once && vos->vos_uberblock.ub_txg == 0) {
+		/*
+		 * This can happen when we added an object store vdev to a
+		 * block-based pool and the agent died before we managed to
+		 * sync a single TXG/uberblock to the object store.
+		 */
+		ASSERT0(vos->vos_uberblock.ub_magic);
+		ASSERT0(vos->vos_uberblock.ub_guid_sum);
+		ASSERT0(vos->vos_uberblock.ub_timestamp);
+		return (0);
+	}
 	return (SET_ERROR(EBUSY));
 }
 
@@ -1486,6 +1500,7 @@ object_store_end_txg(vdev_t *vd, nvlist_t *config, uint64_t txg)
 	ASSERT3U(len, ==, vos->vos_free_list_len);
 	vos->vos_free_list_len = 0;
 	vos->vos_send_txg_selector = VOS_TXG_NONE;
+	vos->vos_synced_once = B_TRUE;
 }
 
 void
@@ -2428,6 +2443,11 @@ vdev_object_store_open(vdev_t *vd, uint64_t *psize, uint64_t *max_psize,
 		error = agent_open_pool(vd, vos,
 		    vdev_object_store_open_mode(spa_mode(vd->vdev_spa)),
 		    B_FALSE);
+		/*
+		 * Now that we've opened the pool, check if we've ever synced
+		 * an uberblock to the object store.
+		 */
+		vos->vos_synced_once = (vos->vos_uberblock.ub_txg > 0);
 	}
 
 	/*