MFV 314243

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

illumos/illumos-gate@40510e8eba18690b9a9843b26393725eeb0f1dac
https://github.com/illumos/illumos-gate/commit/40510e8eba18690b9a9843b26393725eeb0f1dac

https://www.illumos.org/issues/6676

  The fsid of zfs filesystems might change after reboot or remount. The problem seems to
  be caused by a race between unique_insert() and unique_remove(). The unique_remove()
  is called from dsl_dataset_evict() which is now an asynchronous thread. In a case the
  dsl_dataset_evict() thread is very slow and calls unique_remove() too late we will end
  up with changed fsid on zfs mount.

  This problem is very likely caused by #5056.

  Steps to Reproduce
  Note: I'm able to reproduce this always on a single core (virtual) machine. On multicore
  machines it is not so easy to reproduce.

# uname -a
SunOS openindiana 5.11 illumos-633aa80 i86pc i386 i86pc Solaris
# zfs create rpool/TEST
# FS=$(echo ::fsinfo | mdb -k | grep TEST | awk '{print $1}')
# echo $FS::print vfs_t vfs_fsid | mdb -k
vfs_fsid = {
    vfs_fsid.val = [ 0x54d7028a, 0x70311508 ]
}
# zfs umount rpool/TEST
# zfs mount rpool/TEST
# FS=$(echo ::fsinfo | mdb -k | grep TEST | awk '{print $1}')
# echo $FS::print vfs_t vfs_fsid | mdb -k
vfs_fsid = {
    vfs_fsid.val = [ 0xd9454e49, 0x6b36d08 ]
}
#

  Impact
  The persistent fsid (filesystem id) is essential for proper NFS functionality.
  If the fsid of a filesystem changes on remount (or after reboot) the NFS
  clients might not be able to automatically recover from such event and the
  manual remount of the NFS filesystems on every NFS client might be needed.

Author: 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>

9 files changed, 90 insertions, 36 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
index 40b217e4daad..5a873a149cbe 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
@@ -54,7 +54,9 @@ 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 */
 
 /*
@@ -361,11 +363,24 @@ 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);
+	boolean_t 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
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
index 9c618d932755..8bcb6cbede72 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
@@ -1014,7 +1014,7 @@ 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;
@@ -1140,8 +1140,8 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag,
 		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) {
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
index 5053bdf7d6fe..01dd3d8aab30 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
@@ -21,7 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2011 Martin Matuska <mm@FreeBSD.org>
- * 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.
@@ -279,16 +279,30 @@ 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);
 
-	ds->ds_dbuf = NULL;
-
 	unique_remove(ds->ds_fsid_guid);
+}
+
+static void
+dsl_dataset_evict_async(void *dbu)
+{
+	dsl_dataset_t *ds = dbu;
+
+	ASSERT(ds->ds_owner == NULL);
+
+	ds->ds_dbuf = NULL;
 
 	if (ds->ds_objset != NULL)
 		dmu_objset_evict(ds->ds_objset);
@@ -528,7 +542,8 @@ 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);
 
@@ -551,6 +566,16 @@ 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);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
index 224575e951d7..3bb6a02c5483 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
@@ -22,7 +22,7 @@
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2011 Pawel Jakub Dawidek <pawel@dawidek.net>.
  * All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014 Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright 2015 Nexenta Systems, Inc. All rights reserved.
@@ -133,7 +133,7 @@ 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;
 	dsl_pool_t *dp = dd->dd_pool;
@@ -240,7 +240,8 @@ 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)
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sa.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sa.c
index e11dd4db0185..853059c3526b 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sa.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sa.c
@@ -22,7 +22,7 @@
 /*
  * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright 2011 iXsystems, Inc
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2013, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  */
@@ -1299,7 +1299,7 @@ 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");
 }
@@ -1383,7 +1383,8 @@ 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;
@@ -1394,7 +1395,8 @@ 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);
 		}
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
index b405e1e70e9f..ae09e14385ad 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
@@ -539,8 +539,14 @@ typedef struct dmu_buf_user {
 	 */
 	taskq_ent_t	dbu_tqent;
 
-	/* This instance's eviction function pointer. */
-	dmu_buf_evict_func_t *dbu_evict_func;
+	/*
+	 * This instance's eviction function pointers.
+	 *
+	 * dbu_evict_func_sync is called synchronously and then
+	 * dbu_evict_func_async is executed asynchronously on a taskq.
+	 */
+	dmu_buf_evict_func_t *dbu_evict_func_sync;
+	dmu_buf_evict_func_t *dbu_evict_func_async;
 #ifdef ZFS_DEBUG
 	/*
 	 * Pointer to user's dbuf pointer.  NULL for clients that do
@@ -564,15 +570,19 @@ typedef struct dmu_buf_user {
 /* Very ugly, but it beats issuing suppression directives in many Makefiles. */
 extern 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_async, dmu_buf_t **clear_on_evict_dbufp);
 #else /* __lint */
 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_init_user(dmu_buf_user_t *dbu, dmu_buf_evict_func_t *evict_func_sync,
+    dmu_buf_evict_func_t *evict_func_async, dmu_buf_t **clear_on_evict_dbufp)
 {
-	ASSERT(dbu->dbu_evict_func == NULL);
-	ASSERT(evict_func != NULL);
-	dbu->dbu_evict_func = evict_func;
+	ASSERT(dbu->dbu_evict_func_sync == NULL);
+	ASSERT(dbu->dbu_evict_func_async == NULL);
+
+	/* must have at least one evict func */
+	IMPLY(evict_func_sync == NULL, evict_func_async != NULL);
+	dbu->dbu_evict_func_sync = evict_func_sync;
+	dbu->dbu_evict_func_async = evict_func_async;
 #ifdef ZFS_DEBUG
 	dbu->dbu_clear_on_evict_dbufp = clear_on_evict_dbufp;
 #endif
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap_impl.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap_impl.h
index dc522f9f7b6f..ea30e923f460 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap_impl.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap_impl.h
@@ -199,7 +199,7 @@ boolean_t zap_match(zap_name_t *zn, const char *matchname);
 int zap_lockdir(objset_t *os, uint64_t obj, dmu_tx_t *tx,
     krw_t lti, boolean_t fatreader, boolean_t adding, void *tag, zap_t **zapp);
 void zap_unlockdir(zap_t *zap, void *tag);
-void zap_evict(void *dbu);
+void zap_evict_sync(void *dbu);
 zap_name_t *zap_name_alloc(zap_t *zap, const char *key, matchtype_t mt);
 void zap_name_free(zap_name_t *zn);
 int zap_hashbits(zap_t *zap);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c
index 7050d6a341a2..e0bea807d589 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/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;
 	}
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
index c836a3182dc5..67644a08b3fc 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap_micro.c
@@ -403,7 +403,7 @@ 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)
@@ -747,7 +747,7 @@ 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;