From fdffb9e44b7f40c2307d7bee515cc619c3c98617 Mon Sep 17 00:00:00 2001
From: Tim Chase <tim@chase2k.com>
Date: Wed, 16 Oct 2013 13:56:03 -0500
Subject: [PATCH] zfs_unmount_snap() should return 0 if the snapshot it's
 passed is not a snapshot.  Detect this indirectly by testing zsb as set by
 zfs_sb_hold(). This will normally happen in the case of deleting a zvol's
 snapshot.

---
 module/zfs/zfs_ioctl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 2333867146df..28dd26741a86 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -3370,6 +3370,10 @@ zfs_unmount_snap(const char *snapname)
 	fullname = strdup(snapname);
 
 	err = zfs_sb_hold(dsname, FTAG, &zsb, B_FALSE);
+	if (zsb == NULL) {
+		err = 0;
+		goto out;
+	}
 	if (err != 0)
 		goto out;