OpenZFS 6676 - Race between unique_insert() and unique_remove() causes ZFS fsid change

Authored by: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: Sanjay Nadkarni <sanjay.nadkarni@nexenta.com>
Reviewed by: Dan Vatca <dan.vatca@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/6676
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/40510e8
Closes #5667

module/zfs/dbuf.c

@@ -85,7 +85,9 @@ static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);
 
 #ifndef __lint
 extern inline void dmu_buf_init_user(dmu_buf_user_t *dbu,
-    dmu_buf_evict_func_t *evict_func, dmu_buf_t **clear_on_evict_dbufp);
+    dmu_buf_evict_func_t *evict_func_sync,
+    dmu_buf_evict_func_t *evict_func_async,
+    dmu_buf_t **clear_on_evict_dbufp);
 #endif /* ! __lint */
 
 /*
@@ -385,6 +387,7 @@ static void
 dbuf_evict_user(dmu_buf_impl_t *db)
 {
 	dmu_buf_user_t *dbu = db->db_user;
+	boolean_t has_async;
 
 	ASSERT(MUTEX_HELD(&db->db_mtx));
 
@@ -400,11 +403,24 @@ dbuf_evict_user(dmu_buf_impl_t *db)
 #endif
 
 	/*
-	 * Invoke the callback from a taskq to avoid lock order reversals
-	 * and limit stack depth.
+	 * There are two eviction callbacks - one that we call synchronously
+	 * and one that we invoke via a taskq.  The async one is useful for
+	 * avoiding lock order reversals and limiting stack depth.
+	 *
+	 * Note that if we have a sync callback but no async callback,
+	 * it's likely that the sync callback will free the structure
+	 * containing the dbu.  In that case we need to take care to not
+	 * dereference dbu after calling the sync evict func.
 	 */
-	taskq_dispatch_ent(dbu_evict_taskq, dbu->dbu_evict_func, dbu, 0,
-	    &dbu->dbu_tqent);
+	has_async = (dbu->dbu_evict_func_async != NULL);
+
+	if (dbu->dbu_evict_func_sync != NULL)
+		dbu->dbu_evict_func_sync(dbu);
+
+	if (has_async) {
+		taskq_dispatch_ent(dbu_evict_taskq, dbu->dbu_evict_func_async,
+		    dbu, 0, &dbu->dbu_tqent);
+	}
 }
 
 boolean_t

module/zfs/dnode.c

@@ -1021,7 +1021,7 @@ dnode_special_open(objset_t *os, dnode_phys_t *dnp, uint64_t object,
 }
 
 static void
-dnode_buf_pageout(void *dbu)
+dnode_buf_evict_async(void *dbu)
 {
 	dnode_children_t *children_dnodes = dbu;
 	int i;
@@ -1271,8 +1271,8 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 		for (i = 0; i < epb; i++) {
 			zrl_init(&dnh[i].dnh_zrlock);
 		}
-		dmu_buf_init_user(&children_dnodes->dnc_dbu,
-		    dnode_buf_pageout, NULL);
+		dmu_buf_init_user(&children_dnodes->dnc_dbu, NULL,
+		    dnode_buf_evict_async, NULL);
 		winner = dmu_buf_set_user(&db->db, &children_dnodes->dnc_dbu);
 		if (winner != NULL) {
 

module/zfs/dsl_dataset.c

@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 RackTop Systems.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
@@ -273,8 +273,24 @@ dsl_dataset_block_freeable(dsl_dataset_t *ds, const blkptr_t *bp,
 	return (B_TRUE);
 }
 
+/*
+ * We have to release the fsid syncronously or we risk that a subsequent
+ * mount of the same dataset will fail to unique_insert the fsid.  This
+ * failure would manifest itself as the fsid of this dataset changing
+ * between mounts which makes NFS clients quite unhappy.
+ */
 static void
-dsl_dataset_evict(void *dbu)
+dsl_dataset_evict_sync(void *dbu)
+{
+	dsl_dataset_t *ds = dbu;
+
+	ASSERT(ds->ds_owner == NULL);
+
+	unique_remove(ds->ds_fsid_guid);
+}
+
+static void
+dsl_dataset_evict_async(void *dbu)
 {
 	dsl_dataset_t *ds = dbu;
 
@@ -282,8 +298,6 @@ dsl_dataset_evict(void *dbu)
 
 	ds->ds_dbuf = NULL;
 
-	unique_remove(ds->ds_fsid_guid);
-
 	if (ds->ds_objset != NULL)
 		dmu_objset_evict(ds->ds_objset);
 
@@ -525,7 +539,8 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 			ds->ds_reserved = ds->ds_quota = 0;
 		}
 
-		dmu_buf_init_user(&ds->ds_dbu, dsl_dataset_evict, &ds->ds_dbuf);
+		dmu_buf_init_user(&ds->ds_dbu, dsl_dataset_evict_sync,
+		    dsl_dataset_evict_async, &ds->ds_dbuf);
 		if (err == 0)
 			winner = dmu_buf_set_user_ie(dbuf, &ds->ds_dbu);
 
@@ -548,6 +563,16 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		} else {
 			ds->ds_fsid_guid =
 			    unique_insert(dsl_dataset_phys(ds)->ds_fsid_guid);
+			if (ds->ds_fsid_guid !=
+			    dsl_dataset_phys(ds)->ds_fsid_guid) {
+				zfs_dbgmsg("ds_fsid_guid changed from "
+				    "%llx to %llx for pool %s dataset id %llu",
+				    (long long)
+				    dsl_dataset_phys(ds)->ds_fsid_guid,
+				    (long long)ds->ds_fsid_guid,
+				    spa_name(dp->dp_spa),
+				    dsobj);
+			}
 		}
 	}
 	ASSERT3P(ds->ds_dbuf, ==, dbuf);

module/zfs/dsl_dir.c

@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
  * 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.
@@ -129,7 +129,7 @@ extern inline dsl_dir_phys_t *dsl_dir_phys(dsl_dir_t *dd);
 static uint64_t dsl_dir_space_towrite(dsl_dir_t *dd);
 
 static void
-dsl_dir_evict(void *dbu)
+dsl_dir_evict_async(void *dbu)
 {
 	dsl_dir_t *dd = dbu;
 	int t;
@@ -237,7 +237,8 @@ dsl_dir_hold_obj(dsl_pool_t *dp, uint64_t ddobj,
 			dmu_buf_rele(origin_bonus, FTAG);
 		}
 
-		dmu_buf_init_user(&dd->dd_dbu, dsl_dir_evict, &dd->dd_dbuf);
+		dmu_buf_init_user(&dd->dd_dbu, NULL, dsl_dir_evict_async,
+		    &dd->dd_dbuf);
 		winner = dmu_buf_set_user_ie(dbuf, &dd->dd_dbu);
 		if (winner != NULL) {
 			if (dd->dd_parent)

module/zfs/sa.c

@@ -21,7 +21,7 @@
 
 /*
  * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  */
 
@@ -1297,7 +1297,7 @@ sa_build_index(sa_handle_t *hdl, sa_buf_type_t buftype)
 
 /*ARGSUSED*/
 static void
-sa_evict(void *dbu)
+sa_evict_sync(void *dbu)
 {
 	panic("evicting sa dbuf\n");
 }
@@ -1394,7 +1394,8 @@ sa_handle_get_from_db(objset_t *os, dmu_buf_t *db, void *userp,
 		sa_handle_t *winner = NULL;
 
 		handle = kmem_cache_alloc(sa_cache, KM_SLEEP);
-		handle->sa_dbu.dbu_evict_func = NULL;
+		handle->sa_dbu.dbu_evict_func_sync = NULL;
+		handle->sa_dbu.dbu_evict_func_async = NULL;
 		handle->sa_userp = userp;
 		handle->sa_bonus = db;
 		handle->sa_os = os;
@@ -1405,7 +1406,8 @@ sa_handle_get_from_db(objset_t *os, dmu_buf_t *db, void *userp,
 		error = sa_build_index(handle, SA_BONUS);
 
 		if (hdl_type == SA_HDL_SHARED) {
-			dmu_buf_init_user(&handle->sa_dbu, sa_evict, NULL);
+			dmu_buf_init_user(&handle->sa_dbu, sa_evict_sync, NULL,
+			    NULL);
 			winner = dmu_buf_set_user_ie(db, &handle->sa_dbu);
 		}
 

module/zfs/zap.c

@@ -81,7 +81,8 @@ fzap_upgrade(zap_t *zap, dmu_tx_t *tx, zap_flags_t flags)
 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
 	zap->zap_ismicro = FALSE;
 
-	zap->zap_dbu.dbu_evict_func = zap_evict;
+	zap->zap_dbu.dbu_evict_func_sync = zap_evict_sync;
+	zap->zap_dbu.dbu_evict_func_async = NULL;
 
 	mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, 0, 0);
 	zap->zap_f.zap_block_shift = highbit64(zap->zap_dbuf->db_size) - 1;
@@ -399,7 +400,7 @@ zap_allocate_blocks(zap_t *zap, int nblocks)
 }
 
 static void
-zap_leaf_pageout(void *dbu)
+zap_leaf_evict_sync(void *dbu)
 {
 	zap_leaf_t *l = dbu;
 
@@ -423,7 +424,7 @@ zap_create_leaf(zap_t *zap, dmu_tx_t *tx)
 	VERIFY(0 == dmu_buf_hold(zap->zap_objset, zap->zap_object,
 	    l->l_blkid << FZAP_BLOCK_SHIFT(zap), NULL, &l->l_dbuf,
 	    DMU_READ_NO_PREFETCH));
-	dmu_buf_init_user(&l->l_dbu, zap_leaf_pageout, &l->l_dbuf);
+	dmu_buf_init_user(&l->l_dbu, zap_leaf_evict_sync, NULL, &l->l_dbuf);
 	winner = dmu_buf_set_user(l->l_dbuf, &l->l_dbu);
 	ASSERT(winner == NULL);
 	dmu_buf_will_dirty(l->l_dbuf, tx);
@@ -470,13 +471,13 @@ zap_open_leaf(uint64_t blkid, dmu_buf_t *db)
 	l->l_bs = highbit64(db->db_size) - 1;
 	l->l_dbuf = db;
 
-	dmu_buf_init_user(&l->l_dbu, zap_leaf_pageout, &l->l_dbuf);
+	dmu_buf_init_user(&l->l_dbu, zap_leaf_evict_sync, NULL, &l->l_dbuf);
 	winner = dmu_buf_set_user(db, &l->l_dbu);
 
 	rw_exit(&l->l_rwlock);
 	if (winner != NULL) {
 		/* someone else set it first */
-		zap_leaf_pageout(&l->l_dbu);
+		zap_leaf_evict_sync(&l->l_dbu);
 		l = winner;
 	}
 

module/zfs/zap_micro.c

@@ -392,7 +392,7 @@ mzap_open(objset_t *os, uint64_t obj, dmu_buf_t *db)
 	 * it, because zap_lockdir() checks zap_ismicro without the lock
 	 * held.
 	 */
-	dmu_buf_init_user(&zap->zap_dbu, zap_evict, &zap->zap_dbuf);
+	dmu_buf_init_user(&zap->zap_dbu, zap_evict_sync, NULL, &zap->zap_dbuf);
 	winner = dmu_buf_set_user(db, &zap->zap_dbu);
 
 	if (winner != NULL)
@@ -774,7 +774,7 @@ zap_destroy(objset_t *os, uint64_t zapobj, dmu_tx_t *tx)
 }
 
 void
-zap_evict(void *dbu)
+zap_evict_sync(void *dbu)
 {
 	zap_t *zap = dbu;