Add support for asynchronous zvol minor operations

zfsonlinux issue openzfs#2217 - zvol minor operations: check snapdev
property before traversing snapshots of a dataset

zfsonlinux issue openzfs#3681 - lock order inversion between zvol_open()
and dsl_pool_sync()...zvol_rename_minors()

Create a per-pool zvol taskq for asynchronous zvol tasks.
There are a few key design decisions to be aware of.

* Each taskq must be single threaded to ensure tasks are always
  processed in the order in which they were dispatched.

* There is a taskq per-pool in order to keep the pools independent.
  This way if one pool is suspended it will not impact another.

* The preferred location to dispatch a zvol minor task is a sync
  task.  In this context there is easy access to the spa_t and
  minimal error handling is required because the sync task must
  succeed.

Support for asynchronous zvol minor operations address issue openzfs#3681.

Signed-off-by: Boris Protopopov <boris.protopopov@actifio.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#2217
Closes openzfs#3678
Closes openzfs#3681

include/sys/spa_impl.h

@@ -23,6 +23,7 @@
  * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #ifndef _SYS_SPA_IMPL_H
@@ -253,6 +254,7 @@ struct spa {
 	uint64_t	spa_errata;		/* errata issues detected */
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
 	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
+	taskq_t		*spa_zvol_taskq;	/* Taskq for minor managment */
 
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements

include/sys/zvol.h

@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2006, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #ifndef	_SYS_ZVOL_H
@@ -31,24 +32,22 @@
 #define	ZVOL_OBJ		1ULL
 #define	ZVOL_ZAP_OBJ		2ULL
 
-#ifdef _KERNEL
+extern void zvol_create_minors(spa_t *spa, const char *name, boolean_t async);
+extern void zvol_remove_minors(spa_t *spa, const char *name, boolean_t async);
+extern void zvol_rename_minors(spa_t *spa, const char *oldname,
+    const char *newname, boolean_t async);
 
+#ifdef _KERNEL
 extern int zvol_check_volsize(uint64_t volsize, uint64_t blocksize);
 extern int zvol_check_volblocksize(const char *name, uint64_t volblocksize);
 extern int zvol_get_stats(objset_t *os, nvlist_t *nv);
 extern boolean_t zvol_is_zvol(const char *);
 extern void zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx);
-extern int zvol_create_minor(const char *name);
-extern int zvol_create_minors(const char *name);
-extern int zvol_remove_minor(const char *name);
-extern void zvol_remove_minors(const char *name);
-extern void zvol_rename_minors(const char *oldname, const char *newname);
 extern int zvol_set_volsize(const char *, uint64_t);
 extern int zvol_set_volblocksize(const char *, uint64_t);
-extern int zvol_set_snapdev(const char *, uint64_t);
+extern int zvol_set_snapdev(const char *, zprop_source_t, uint64_t);
 
 extern int zvol_init(void);
 extern void zvol_fini(void);
-
 #endif /* _KERNEL */
 #endif /* _SYS_ZVOL_H */

lib/libzpool/kernel.c

@@ -20,6 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <assert.h>
@@ -1354,3 +1355,24 @@ spl_fstrans_check(void)
 {
 	return (0);
 }
+
+void
+zvol_create_minors(spa_t *spa, const char *name, boolean_t async)
+{
+}
+
+void
+zvol_remove_minor(spa_t *spa, const char *name, boolean_t async)
+{
+}
+
+void
+zvol_remove_minors(spa_t *spa, const char *name, boolean_t async)
+{
+}
+
+void
+zvol_rename_minors(spa_t *spa, const char *oldname, const char *newname,
+    boolean_t async)
+{
+}

module/zfs/dmu_objset.c

@@ -26,6 +26,7 @@
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright (c) 2015 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2015, STRATO AG, Inc. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 /* Portions Copyright 2010 Robert Milkowski */
@@ -868,6 +869,8 @@ dmu_objset_create_sync(void *arg, dmu_tx_t *tx)
 	}
 
 	spa_history_log_internal_ds(ds, "create", tx, "");
+	zvol_create_minors(dp->dp_spa, doca->doca_name, B_TRUE);
+
 	dsl_dataset_rele(ds, FTAG);
 	dsl_dir_rele(pdd, FTAG);
 }
@@ -961,6 +964,7 @@ dmu_objset_clone_sync(void *arg, dmu_tx_t *tx)
 	dsl_dataset_name(origin, namebuf);
 	spa_history_log_internal_ds(ds, "clone", tx,
 	    "origin=%s (%llu)", namebuf, origin->ds_object);
+	zvol_create_minors(dp->dp_spa, doca->doca_clone, B_TRUE);
 	dsl_dataset_rele(ds, FTAG);
 	dsl_dataset_rele(origin, FTAG);
 	dsl_dir_rele(pdd, FTAG);

module/zfs/dmu_send.c

@@ -24,6 +24,7 @@
  * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
  * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <sys/dmu.h>
@@ -54,6 +55,7 @@
 #include <sys/dsl_bookmark.h>
 #include <sys/zfeature.h>
 #include <sys/bqueue.h>
+#include <sys/zvol.h>
 
 /* Set this tunable to TRUE to replace corrupt data with 0x2f5baddb10c */
 int zfs_send_corrupt_data = B_FALSE;
@@ -2646,6 +2648,7 @@ dmu_recv_end_sync(void *arg, dmu_tx_t *tx)
 		dsl_dataset_phys(ds)->ds_flags &= ~DS_FLAG_INCONSISTENT;
 	}
 	drc->drc_newsnapobj = dsl_dataset_phys(drc->drc_ds)->ds_prev_snap_obj;
+	zvol_create_minors(dp->dp_spa, drc->drc_tofs, B_TRUE);
 	/*
 	 * Release the hold from dmu_recv_begin.  This must be done before
 	 * we return to open context, so that when we free the dataset's dnode,

module/zfs/dsl_dataset.c

@@ -24,6 +24,7 @@
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 RackTop Systems.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <sys/dmu_objset.h>
@@ -1424,6 +1425,7 @@ dsl_dataset_snapshot_sync(void *arg, dmu_tx_t *tx)
 			dsl_props_set_sync_impl(ds->ds_prev,
 			    ZPROP_SRC_LOCAL, ddsa->ddsa_props, tx);
 		}
+		zvol_create_minors(dp->dp_spa, nvpair_name(pair), B_TRUE);
 		dsl_dataset_rele(ds, FTAG);
 	}
 }
@@ -1498,16 +1500,6 @@ dsl_dataset_snapshot(nvlist_t *snaps, nvlist_t *props, nvlist_t *errors)
 		fnvlist_free(suspended);
 	}
 
-#ifdef _KERNEL
-	if (error == 0) {
-		for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
-		    pair = nvlist_next_nvpair(snaps, pair)) {
-			char *snapname = nvpair_name(pair);
-			zvol_create_minors(snapname);
-		}
-	}
-#endif
-
 	return (error);
 }
 
@@ -1930,6 +1922,8 @@ dsl_dataset_rename_snapshot_sync_impl(dsl_pool_t *dp,
 	VERIFY0(zap_add(dp->dp_meta_objset,
 	    dsl_dataset_phys(hds)->ds_snapnames_zapobj,
 	    ds->ds_snapname, 8, 1, &ds->ds_object, tx));
+	zvol_rename_minors(dp->dp_spa, ddrsa->ddrsa_oldsnapname,
+	    ddrsa->ddrsa_newsnapname, B_TRUE);
 
 	dsl_dataset_rele(ds, FTAG);
 	return (0);
@@ -1958,34 +1952,16 @@ int
 dsl_dataset_rename_snapshot(const char *fsname,
     const char *oldsnapname, const char *newsnapname, boolean_t recursive)
 {
-#ifdef _KERNEL
-	char *oldname, *newname;
-#endif
-	int error;
-
 	dsl_dataset_rename_snapshot_arg_t ddrsa;
 
 	ddrsa.ddrsa_fsname = fsname;
 	ddrsa.ddrsa_oldsnapname = oldsnapname;
 	ddrsa.ddrsa_newsnapname = newsnapname;
 	ddrsa.ddrsa_recursive = recursive;
 
-	error = dsl_sync_task(fsname, dsl_dataset_rename_snapshot_check,
+	return (dsl_sync_task(fsname, dsl_dataset_rename_snapshot_check,
 	    dsl_dataset_rename_snapshot_sync, &ddrsa,
-	    1, ZFS_SPACE_CHECK_RESERVED);
-
-	if (error)
-	    return (SET_ERROR(error));
-
-#ifdef _KERNEL
-	oldname = kmem_asprintf("%s@%s", fsname, oldsnapname);
-	newname = kmem_asprintf("%s@%s", fsname, newsnapname);
-	zvol_rename_minors(oldname, newname);
-	strfree(newname);
-	strfree(oldname);
-#endif
-
-	return (0);
+	    1, ZFS_SPACE_CHECK_RESERVED));
 }
 
 /*

module/zfs/dsl_destroy.c

@@ -23,6 +23,7 @@
  * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
  * Copyright (c) 2013 by Joyent, Inc. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -40,6 +41,7 @@
 #include <sys/zfs_ioctl.h>
 #include <sys/dsl_deleg.h>
 #include <sys/dmu_impl.h>
+#include <sys/zvol.h>
 
 typedef struct dmu_snapshots_destroy_arg {
 	nvlist_t *dsda_snaps;
@@ -243,9 +245,6 @@ dsl_dataset_remove_clones_key(dsl_dataset_t *ds, uint64_t mintxg, dmu_tx_t *tx)
 void
 dsl_destroy_snapshot_sync_impl(dsl_dataset_t *ds, boolean_t defer, dmu_tx_t *tx)
 {
-#ifdef ZFS_DEBUG
-	int err;
-#endif
 	spa_feature_t f;
 	int after_branch_point = FALSE;
 	dsl_pool_t *dp = ds->ds_dir->dd_pool;
@@ -441,6 +440,7 @@ dsl_destroy_snapshot_sync_impl(dsl_dataset_t *ds, boolean_t defer, dmu_tx_t *tx)
 #ifdef ZFS_DEBUG
 	{
 		uint64_t val;
+		int err;
 
 		err = dsl_dataset_snap_lookup(ds_head,
 		    ds->ds_snapname, &val);
@@ -490,6 +490,7 @@ dsl_destroy_snapshot_sync(void *arg, dmu_tx_t *tx)
 		VERIFY0(dsl_dataset_hold(dp, nvpair_name(pair), FTAG, &ds));
 
 		dsl_destroy_snapshot_sync_impl(ds, dsda->dsda_defer, tx);
+		zvol_remove_minors(dp->dp_spa, nvpair_name(pair), B_TRUE);
 		dsl_dataset_rele(ds, FTAG);
 	}
 }
@@ -889,6 +890,7 @@ dsl_destroy_head_sync(void *arg, dmu_tx_t *tx)
 
 	VERIFY0(dsl_dataset_hold(dp, ddha->ddha_name, FTAG, &ds));
 	dsl_destroy_head_sync_impl(ds, tx);
+	zvol_remove_minors(dp->dp_spa, ddha->ddha_name, B_TRUE);
 	dsl_dataset_rele(ds, FTAG);
 }
 

module/zfs/dsl_dir.c

@@ -24,6 +24,7 @@
  * Copyright (c) 2013 Martin Matuska. All rights reserved.
  * Copyright (c) 2014 Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <sys/dmu.h>
@@ -1909,9 +1910,8 @@ dsl_dir_rename_sync(void *arg, dmu_tx_t *tx)
 	VERIFY0(zap_add(mos, dsl_dir_phys(newparent)->dd_child_dir_zapobj,
 	    dd->dd_myname, 8, 1, &dd->dd_object, tx));
 
-#ifdef _KERNEL
-	zvol_rename_minors(ddra->ddra_oldname, ddra->ddra_newname);
-#endif
+	zvol_rename_minors(dp->dp_spa, ddra->ddra_oldname,
+	    ddra->ddra_newname, B_TRUE);
 
 	dsl_prop_notify_all(dd);
 

module/zfs/spa.c

@@ -24,6 +24,7 @@
  * Copyright (c) 2013 by Delphix. All rights reserved.
  * Copyright (c) 2013, 2014, Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 /*
@@ -1136,6 +1137,24 @@ spa_activate(spa_t *spa, int mode)
 	avl_create(&spa->spa_errlist_last,
 	    spa_error_entry_compare, sizeof (spa_error_entry_t),
 	    offsetof(spa_error_entry_t, se_avl));
+
+	/*
+	 * This taskq is used to perform zvol-minor-related tasks
+	 * asynchronously. This has several advantages, including easy
+	 * resolution of various deadlocks (zfsonlinux bug #3681).
+	 *
+	 * The taskq must be single threaded to ensure tasks are always
+	 * processed in the order in which they were dispatched.
+	 *
+	 * A taskq per pool allows one to keep the pools independent.
+	 * This way if one pool is suspended, it will not impact another.
+	 *
+	 * The preferred location to dispatch a zvol minor task is a sync
+	 * task. In this context, there is easy access to the spa_t and minimal
+	 * error handling is required because the sync task must succeed.
+	 */
+	spa->spa_zvol_taskq = taskq_create("z_zvol", 1, defclsyspri,
+	    1, INT_MAX, 0);
 }
 
 /*
@@ -1154,6 +1173,11 @@ spa_deactivate(spa_t *spa)
 
 	spa_evicting_os_wait(spa);
 
+	if (spa->spa_zvol_taskq) {
+		taskq_destroy(spa->spa_zvol_taskq);
+		spa->spa_zvol_taskq = NULL;
+	}
+
 	txg_list_destroy(&spa->spa_vdev_txg_list);
 
 	list_destroy(&spa->spa_config_dirty_list);
@@ -3088,10 +3112,8 @@ spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
 		mutex_exit(&spa_namespace_lock);
 	}
 
-#ifdef _KERNEL
 	if (firstopen)
-		zvol_create_minors(spa->spa_name);
-#endif
+		zvol_create_minors(spa, spa_name(spa), B_TRUE);
 
 	*spapp = spa;
 
@@ -4211,10 +4233,7 @@ spa_import(char *pool, nvlist_t *config, nvlist_t *props, uint64_t flags)
 
 	mutex_exit(&spa_namespace_lock);
 	spa_history_log_version(spa, "import");
-
-#ifdef _KERNEL
-	zvol_create_minors(pool);
-#endif
+	zvol_create_minors(spa, pool, B_TRUE);
 
 	return (0);
 }
@@ -4349,6 +4368,10 @@ spa_export_common(char *pool, int new_state, nvlist_t **oldconfig,
 	spa_open_ref(spa, FTAG);
 	mutex_exit(&spa_namespace_lock);
 	spa_async_suspend(spa);
+	if (spa->spa_zvol_taskq) {
+		zvol_remove_minors(spa, spa_name(spa), B_TRUE);
+		taskq_wait(spa->spa_zvol_taskq);
+	}
 	mutex_enter(&spa_namespace_lock);
 	spa_close(spa, FTAG);