Fix "snapdev" property issues

When inheriting the "snapdev" property to we don't always call
zfs_prop_set_special(): this prevents device nodes from being created in
certain situations. Because "snapdev" is the only *special* property
that is also inheritable we need to call zfs_prop_set_special() even
when we're not reverting it to the received value ('zfs inherit -S').

Additionally, fix a NULL pointer dereference accidentally introduced in
5559ba0 that can be triggered when setting the "snapdev" property to
the value "hidden" twice.

Finally, add a new test case "zvol_misc_snapdev" to the ZFS Test Suite.

Reviewed by: Boris Protopopov <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: loli10K <[email protected]>
Closes #6131 
Closes #6175 
Closes #6176 

1 files changed, 23 insertions, 13 deletions

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index cff3da8b4..1a86cd3cd 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -2018,7 +2018,7 @@ zvol_remove_minors_impl(const char *name)
 static void
 zvol_remove_minor_impl(const char *name)
 {
-	zvol_state_t *zv, *zv_next;
+	zvol_state_t *zv = NULL, *zv_next;
 
 	if (zvol_inhibit_dev)
 		return;
@@ -2049,12 +2049,11 @@ zvol_remove_minor_impl(const char *name)
 		}
 	}
 
+	/* Drop zvol_state_lock before calling zvol_free() */
 	mutex_exit(&zvol_state_lock);
 
-	/*
-	 * Drop zvol_state_lock before calling zvol_free()
-	 */
-	zvol_free(zv);
+	if (zv != NULL)
+		zvol_free(zv);
 }
 
 /*
@@ -2224,20 +2223,18 @@ zvol_set_snapdev_check(void *arg, dmu_tx_t *tx)
 	return (error);
 }
 
+/* ARGSUSED */
 static int
 zvol_set_snapdev_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 {
-	zvol_set_snapdev_arg_t *zsda = arg;
 	char dsname[MAXNAMELEN];
 	zvol_task_t *task;
+	uint64_t snapdev;
 
 	dsl_dataset_name(ds, dsname);
-	dsl_prop_set_sync_impl(ds, zfs_prop_to_name(ZFS_PROP_SNAPDEV),
-	    zsda->zsda_source, sizeof (zsda->zsda_value), 1,
-	    &zsda->zsda_value, zsda->zsda_tx);
-
-	task = zvol_task_alloc(ZVOL_ASYNC_SET_SNAPDEV, dsname,
-	    NULL, zsda->zsda_value);
+	if (dsl_prop_get_int_ds(ds, "snapdev", &snapdev) != 0)
+		return (0);
+	task = zvol_task_alloc(ZVOL_ASYNC_SET_SNAPDEV, dsname, NULL, snapdev);
 	if (task == NULL)
 		return (0);
 
@@ -2247,7 +2244,11 @@ zvol_set_snapdev_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 }
 
 /*
- * Traverse all child snapshot datasets and apply snapdev appropriately.
+ * Traverse all child datasets and apply snapdev appropriately.
+ * We call dsl_prop_set_sync_impl() here to set the value only on the toplevel
+ * dataset and read the effective "snapdev" on every child in the callback
+ * function: this is because the value is not guaranteed to be the same in the
+ * whole dataset hierarchy.
  */
 static void
 zvol_set_snapdev_sync(void *arg, dmu_tx_t *tx)
@@ -2255,10 +2256,19 @@ zvol_set_snapdev_sync(void *arg, dmu_tx_t *tx)
 	zvol_set_snapdev_arg_t *zsda = arg;
 	dsl_pool_t *dp = dmu_tx_pool(tx);
 	dsl_dir_t *dd;
+	dsl_dataset_t *ds;
+	int error;
 
 	VERIFY0(dsl_dir_hold(dp, zsda->zsda_name, FTAG, &dd, NULL));
 	zsda->zsda_tx = tx;
 
+	error = dsl_dataset_hold(dp, zsda->zsda_name, FTAG, &ds);
+	if (error == 0) {
+		dsl_prop_set_sync_impl(ds, zfs_prop_to_name(ZFS_PROP_SNAPDEV),
+		    zsda->zsda_source, sizeof (zsda->zsda_value), 1,
+		    &zsda->zsda_value, zsda->zsda_tx);
+		dsl_dataset_rele(ds, FTAG);
+	}
 	dmu_objset_find_dp(dp, dd->dd_object, zvol_set_snapdev_sync_cb,
 	    zsda, DS_FIND_CHILDREN);