MFV r251622:

ZFS shouldn't ignore errors unmounting snapshots

Illumos ZFS issues:
  3744 zfs shouldn't ignore errors unmounting snapshots

MFC after:      2 weeks

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_userhold.c

@@ -433,7 +433,7 @@ dsl_dataset_user_release_tmp(dsl_pool_t *dp, uint64_t dsobj, const char *htag)
 		dsl_dataset_name(ds, name);
 		dsl_dataset_rele(ds, FTAG);
 		dsl_pool_config_exit(dp, FTAG);
-		zfs_unmount_snap(name);
+		(void) zfs_unmount_snap(name);
 	} else {
 		dsl_pool_config_exit(dp, FTAG);
 	}

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_ioctl.h

@@ -360,7 +360,7 @@ extern int zfs_secpolicy_rename_perms(const char *from,
     const char *to, cred_t *cr);
 extern int zfs_secpolicy_destroy_perms(const char *name, cred_t *cr);
 extern int zfs_busy(void);
-extern void zfs_unmount_snap(const char *);
+extern int zfs_unmount_snap(const char *);
 extern void zfs_destroy_unmount_origin(const char *);
 
 /*

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c

@@ -3405,28 +3405,31 @@ zfs_ioc_log_history(const char *unused, nvlist_t *innvl, nvlist_t *outnvl)
  *
  * This function is best-effort.  Callers must deal gracefully if it
  * remains mounted (or is remounted after this call).
+ *
+ * Returns 0 if the argument is not a snapshot, or it is not currently a
+ * filesystem, or we were able to unmount it.  Returns error code otherwise.
  */
-void
+int
 zfs_unmount_snap(const char *snapname)
 {
 	vfs_t *vfsp;
 	zfsvfs_t *zfsvfs;
+	int err;
 
 	if (strchr(snapname, '@') == NULL)
-		return;
+		return (0);
 
 	vfsp = zfs_get_vfs(snapname);
 	if (vfsp == NULL)
-		return;
+		return (0);
 
 	zfsvfs = vfsp->vfs_data;
 	ASSERT(!dsl_pool_config_held(dmu_objset_pool(zfsvfs->z_os)));
 
-	if (vn_vfswlock(vfsp->vfs_vnodecovered) != 0) {
-		VFS_RELE(vfsp);
-		return;
-	}
+	err = vn_vfswlock(vfsp->vfs_vnodecovered);
 	VFS_RELE(vfsp);
+	if (err != 0)
+		return (SET_ERROR(err));
 
 	/*
 	 * Always force the unmount for snapshots.
@@ -3436,17 +3439,17 @@ zfs_unmount_snap(const char *snapname)
 	(void) dounmount(vfsp, MS_FORCE, kcred);
 #else
 	mtx_lock(&Giant);	/* dounmount() */
-	dounmount(vfsp, MS_FORCE, curthread);
+	(void) dounmount(vfsp, MS_FORCE, curthread);
 	mtx_unlock(&Giant);	/* dounmount() */
 #endif
+	return (0);
 }
 
 /* ARGSUSED */
 static int
 zfs_unmount_snap_cb(const char *snapname, void *arg)
 {
-	zfs_unmount_snap(snapname);
-	return (0);
+	return (zfs_unmount_snap(snapname));
 }
 
 /*
@@ -3469,7 +3472,7 @@ zfs_destroy_unmount_origin(const char *fsname)
 		char originname[MAXNAMELEN];
 		dsl_dataset_name(ds->ds_prev, originname);
 		dmu_objset_rele(os, FTAG);
-		zfs_unmount_snap(originname);
+		(void) zfs_unmount_snap(originname);
 	} else {
 		dmu_objset_rele(os, FTAG);
 	}
@@ -3487,7 +3490,7 @@ zfs_destroy_unmount_origin(const char *fsname)
 static int
 zfs_ioc_destroy_snaps(const char *poolname, nvlist_t *innvl, nvlist_t *outnvl)
 {
-	int poollen;
+	int error, poollen;
 	nvlist_t *snaps;
 	nvpair_t *pair;
 	boolean_t defer;
@@ -3508,7 +3511,9 @@ zfs_ioc_destroy_snaps(const char *poolname, nvlist_t *innvl, nvlist_t *outnvl)
 		    (name[poollen] != '/' && name[poollen] != '@'))
 			return (SET_ERROR(EXDEV));
 
-		zfs_unmount_snap(name);
+		error = zfs_unmount_snap(name);
+		if (error != 0)
+			return (error);
 		(void) zvol_remove_minor(name);
 	}
 
@@ -3527,8 +3532,12 @@ static int
 zfs_ioc_destroy(zfs_cmd_t *zc)
 {
 	int err;
-	if (strchr(zc->zc_name, '@') && zc->zc_objset_type == DMU_OST_ZFS)
-		zfs_unmount_snap(zc->zc_name);
+
+	if (zc->zc_objset_type == DMU_OST_ZFS) {
+		err = zfs_unmount_snap(zc->zc_name);
+		if (err != 0)
+			return (err);
+	}
 
 	if (strchr(zc->zc_name, '@'))
 		err = dsl_destroy_snapshot(zc->zc_name, zc->zc_defer_destroy);
@@ -3574,8 +3583,7 @@ recursive_unmount(const char *fsname, void *arg)
 	char fullname[MAXNAMELEN];
 
 	(void) snprintf(fullname, sizeof (fullname), "%s@%s", fsname, snapname);
-	zfs_unmount_snap(fullname);
-	return (0);
+	return (zfs_unmount_snap(fullname));
 }
 
 /*
@@ -5071,14 +5079,18 @@ static int
 zfs_ioc_release(const char *pool, nvlist_t *holds, nvlist_t *errlist)
 {
 	nvpair_t *pair;
+	int err;
 
 	/*
 	 * The release may cause the snapshot to be destroyed; make sure it
 	 * is not mounted.
 	 */
 	for (pair = nvlist_next_nvpair(holds, NULL); pair != NULL;
-	    pair = nvlist_next_nvpair(holds, pair))
-		zfs_unmount_snap(nvpair_name(pair));
+	    pair = nvlist_next_nvpair(holds, pair)) {
+		err = zfs_unmount_snap(nvpair_name(pair));
+		if (err != 0)
+			return (err);
+	}
 
 	return (dsl_dataset_user_release(holds, errlist));
 }