Make zvol_set_common() block until the operation has completed

This is motivated by a FreeBSD AIO test case which create a zvol with -o
volmode=dev, then immediately tries to open the zvol device file.  The
open occasionally fails with ENOENT.

When a zvol is created without the volmode setting, zvol_create_minors()
blocks until the task is finished, at which point OS-dependent code will
have created a device file.  However, zvol_set_common() may cause the
device file to be destroyed and re-created, at least on FreeBSD, if the
voltype switches from GEOM to DEV.  In this case, we do not block
waiting for the operation to finish, causing the test failure.

Fix the problem by making zvol_set_common() block until the operation
has finished.  In FreeBSD zvol code, use g_waitidle() to block until
asynchronous GEOM operations are done.  This fixes a secondary race
where zvol_os_remove_minor() does not block until the zvol device file
is removed, and the subsequent zvol_os_create_minor() fails because the
(to-be-destroyed) device file already exists.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Mark Johnston <markj@FreeBSD.org>
Closes #18191

module/os/freebsd/zfs/zvol_os.c

@@ -918,7 +918,7 @@ zvol_cdev_open(struct cdev *dev, int flags, int fmt, struct thread *td)
 		return (SET_ERROR(ENXIO));
 
 	mutex_enter(&zv->zv_state_lock);
-	if (zv->zv_zso->zso_dying || zv->zv_flags & ZVOL_REMOVING) {
+	if (zv->zv_flags & ZVOL_REMOVING || zv->zv_zso->zso_dying) {
 		err = SET_ERROR(ENXIO);
 		goto out_locked;
 	}
@@ -1425,6 +1425,7 @@ zvol_os_remove_minor(zvol_state_t *zv)
 		pp->private = NULL;
 		g_wither_geom(pp->geom, ENXIO);
 		g_topology_unlock();
+		g_waitidle(curthread);
 	} else if (zv->zv_volmode == ZFS_VOLMODE_DEV) {
 		struct zvol_state_dev *zsd = &zso->zso_dev;
 		struct cdev *dev = zsd->zsd_cdev;
@@ -1554,6 +1555,7 @@ zvol_os_create_minor(const char *name)
 		g_error_provider(zv->zv_zso->zso_geom.zsg_provider, 0);
 		/* geom was locked inside zvol_alloc() function */
 		g_topology_unlock();
+		g_waitidle(curthread);
 	}
 out_doi:
 	kmem_free(doi, sizeof (dmu_object_info_t));

module/zfs/zvol.c

@@ -1999,6 +1999,10 @@ typedef struct zvol_set_prop_int_arg {
 	uint64_t zsda_value;
 	zprop_source_t zsda_source;
 	zfs_prop_t zsda_prop;
+	taskqid_t zsda_taskqid;
+	boolean_t zsda_dispatched;
+	kmutex_t zsda_lock;
+	kcondvar_t zsda_cv;
 } zvol_set_prop_int_arg_t;
 
 /*
@@ -2029,6 +2033,7 @@ zvol_set_common_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 	char dsname[ZFS_MAX_DATASET_NAME_LEN];
 	zvol_task_t *task;
 	uint64_t prop;
+	taskqid_t id;
 
 	const char *prop_name = zfs_prop_to_name(zsda->zsda_prop);
 	dsl_dataset_name(ds, dsname);
@@ -2047,8 +2052,12 @@ zvol_set_common_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 	}
 	task->zt_value = prop;
 	strlcpy(task->zt_name1, dsname, sizeof (task->zt_name1));
-	(void) taskq_dispatch(dp->dp_spa->spa_zvol_taskq, zvol_task_cb,
-	    task, TQ_SLEEP);
+	id = taskq_dispatch(dp->dp_spa->spa_zvol_taskq, zvol_task_cb, task,
+	    TQ_SLEEP);
+	mutex_enter(&zsda->zsda_lock);
+	if (id != TASKQID_INVALID && id > zsda->zsda_taskqid)
+		zsda->zsda_taskqid = id;
+	mutex_exit(&zsda->zsda_lock);
 	return (0);
 }
 
@@ -2081,6 +2090,11 @@ zvol_set_common_sync(void *arg, dmu_tx_t *tx)
 	dmu_objset_find_dp(dp, dd->dd_object, zvol_set_common_sync_cb,
 	    zsda, DS_FIND_CHILDREN);
 
+	mutex_enter(&zsda->zsda_lock);
+	zsda->zsda_dispatched = TRUE;
+	cv_broadcast(&zsda->zsda_cv);
+	mutex_exit(&zsda->zsda_lock);
+
 	dsl_dir_rele(dd, FTAG);
 }
 
@@ -2089,14 +2103,38 @@ zvol_set_common(const char *ddname, zfs_prop_t prop, zprop_source_t source,
     uint64_t val)
 {
 	zvol_set_prop_int_arg_t zsda;
+	spa_t *spa;
+	int error;
 
 	zsda.zsda_name = ddname;
 	zsda.zsda_source = source;
 	zsda.zsda_value = val;
 	zsda.zsda_prop = prop;
+	zsda.zsda_taskqid = TASKQID_INVALID;
+	zsda.zsda_dispatched = FALSE;
+	mutex_init(&zsda.zsda_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&zsda.zsda_cv, NULL, CV_DEFAULT, NULL);
 
-	return (dsl_sync_task(ddname, zvol_set_common_check,
-	    zvol_set_common_sync, &zsda, 0, ZFS_SPACE_CHECK_NONE));
+	error = spa_open(ddname, &spa, FTAG);
+	if (error != 0)
+		goto out;
+	error = dsl_sync_task(ddname, zvol_set_common_check,
+	    zvol_set_common_sync, &zsda, 0, ZFS_SPACE_CHECK_NONE);
+	if (error == 0) {
+		mutex_enter(&zsda.zsda_lock);
+		while (!zsda.zsda_dispatched)
+			cv_wait(&zsda.zsda_cv, &zsda.zsda_lock);
+		mutex_exit(&zsda.zsda_lock);
+
+		if (zsda.zsda_taskqid != TASKQID_INVALID)
+			taskq_wait_outstanding(spa->spa_zvol_taskq,
+			    zsda.zsda_taskqid);
+	}
+	spa_close(spa, FTAG);
+out:
+	cv_destroy(&zsda.zsda_cv);
+	mutex_destroy(&zsda.zsda_lock);
+	return (error);
 }
 
 void