Some nvlist allocations in hold processing need to use KM_PUSHPAGE.

Commit 95fd54a restructured the
hold/release processing and moved some of the work into the sync task.
The ddura_todelete and the newly-added ddura_chkholds members of the
dsl_dataset_user_release_arg can now be used in the sync task context.

Also, in dsl_dataset_user_hold_sync_one(), tmpholds can be used in the
sync task context.

module/zfs/dsl_userhold.c

@@ -242,7 +242,7 @@ dsl_dataset_user_hold_sync_one(dsl_dataset_t *ds, const char *htag,
 	nvlist_t *tmpholds;
 
 	if (minor != 0)
-		tmpholds = fnvlist_alloc();
+		VERIFY0(nvlist_alloc(&tmpholds, NV_UNIQUE_NAME, KM_PUSHPAGE));
 	else
 		tmpholds = NULL;
 	dsl_dataset_user_hold_sync_one_impl(tmpholds, ds, htag, minor, now, tx);
@@ -600,8 +600,8 @@ dsl_dataset_user_release_impl(nvlist_t *holds, nvlist_t *errlist,
 
 	ddura.ddura_holds = holds;
 	ddura.ddura_errlist = errlist;
-	ddura.ddura_todelete = fnvlist_alloc();
-	ddura.ddura_chkholds = fnvlist_alloc();
+	VERIFY0(nvlist_alloc(&ddura.ddura_todelete, NV_UNIQUE_NAME, KM_PUSHPAGE));
+	VERIFY0(nvlist_alloc(&ddura.ddura_chkholds, NV_UNIQUE_NAME, KM_PUSHPAGE));
 
 	error = dsl_sync_task(pool, dsl_dataset_user_release_check,
 	    dsl_dataset_user_release_sync, &ddura,