ocfs2_dlm: fix cluster-wide refcounting of lock resources

This was previously broken and migration of some locks had to be temporarily
disabled. We use a new (and backward-incompatible) set of network messages
to account for all references to a lock resources held across the cluster.
once these are all freed, the master node may then free the lock resource
memory once its local references are dropped.

Signed-off-by: Kurt Hackel <kurt.hackel@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

7 files changed, 725 insertions, 173 deletions

diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h
index 6b6ff76538c5..9fa427119a3c 100644
--- a/fs/ocfs2/dlm/dlmcommon.h
+++ b/fs/ocfs2/dlm/dlmcommon.h
@@ -222,6 +222,7 @@ static inline void __dlm_set_joining_node(struct dlm_ctxt *dlm,
 #define DLM_LOCK_RES_DIRTY                0x00000008
 #define DLM_LOCK_RES_IN_PROGRESS          0x00000010
 #define DLM_LOCK_RES_MIGRATING            0x00000020
+#define DLM_LOCK_RES_DROPPING_REF         0x00000040
 
 /* max milliseconds to wait to sync up a network failure with a node death */
 #define DLM_NODE_DEATH_WAIT_MAX (5 * 1000)
@@ -265,6 +266,8 @@ struct dlm_lock_resource
 	u8  owner;              //node which owns the lock resource, or unknown
 	u16 state;
 	char lvb[DLM_LVB_LEN];
+	unsigned int inflight_locks;
+	unsigned long refmap[BITS_TO_LONGS(O2NM_MAX_NODES)];
 };
 
 struct dlm_migratable_lock
@@ -367,7 +370,7 @@ enum {
 	DLM_CONVERT_LOCK_MSG,	 /* 504 */
 	DLM_PROXY_AST_MSG,	 /* 505 */
 	DLM_UNLOCK_LOCK_MSG,	 /* 506 */
-	DLM_UNUSED_MSG2,	 /* 507 */
+	DLM_DEREF_LOCKRES_MSG,	 /* 507 */
 	DLM_MIGRATE_REQUEST_MSG, /* 508 */
 	DLM_MIG_LOCKRES_MSG, 	 /* 509 */
 	DLM_QUERY_JOIN_MSG,	 /* 510 */
@@ -417,6 +420,9 @@ struct dlm_master_request
 	u8 name[O2NM_MAX_NAME_LEN];
 };
 
+#define DLM_ASSERT_RESPONSE_REASSERT       0x00000001
+#define DLM_ASSERT_RESPONSE_MASTERY_REF    0x00000002
+
 #define DLM_ASSERT_MASTER_MLE_CLEANUP      0x00000001
 #define DLM_ASSERT_MASTER_REQUERY          0x00000002
 #define DLM_ASSERT_MASTER_FINISH_MIGRATION 0x00000004
@@ -430,6 +436,8 @@ struct dlm_assert_master
 	u8 name[O2NM_MAX_NAME_LEN];
 };
 
+#define DLM_MIGRATE_RESPONSE_MASTERY_REF   0x00000001
+
 struct dlm_migrate_request
 {
 	u8 master;
@@ -648,6 +656,16 @@ struct dlm_finalize_reco
 	__be32 pad2;
 };
 
+struct dlm_deref_lockres
+{
+	u32 pad1;
+	u16 pad2;
+	u8 node_idx;
+	u8 namelen;
+
+	u8 name[O2NM_MAX_NAME_LEN];
+};
+
 static inline enum dlm_status
 __dlm_lockres_state_to_status(struct dlm_lock_resource *res)
 {
@@ -721,8 +739,8 @@ void __dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
 			      struct dlm_lock_resource *res);
 void dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
 			    struct dlm_lock_resource *res);
-void dlm_purge_lockres(struct dlm_ctxt *dlm,
-		       struct dlm_lock_resource *lockres);
+int dlm_purge_lockres(struct dlm_ctxt *dlm,
+		      struct dlm_lock_resource *lockres);
 static inline void dlm_lockres_get(struct dlm_lock_resource *res)
 {
 	/* This is called on every lookup, so it might be worth
@@ -733,6 +751,10 @@ void dlm_lockres_put(struct dlm_lock_resource *res);
 void __dlm_unhash_lockres(struct dlm_lock_resource *res);
 void __dlm_insert_lockres(struct dlm_ctxt *dlm,
 			  struct dlm_lock_resource *res);
+struct dlm_lock_resource * __dlm_lookup_lockres_full(struct dlm_ctxt *dlm,
+						     const char *name,
+						     unsigned int len,
+						     unsigned int hash);
 struct dlm_lock_resource * __dlm_lookup_lockres(struct dlm_ctxt *dlm,
 						const char *name,
 						unsigned int len,
@@ -753,6 +775,47 @@ struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
 					  const char *name,
 					  unsigned int namelen);
 
+#define dlm_lockres_set_refmap_bit(bit,res)  \
+	__dlm_lockres_set_refmap_bit(bit,res,__FILE__,__LINE__)
+#define dlm_lockres_clear_refmap_bit(bit,res)  \
+	__dlm_lockres_clear_refmap_bit(bit,res,__FILE__,__LINE__)
+
+static inline void __dlm_lockres_set_refmap_bit(int bit,
+						struct dlm_lock_resource *res,
+						const char *file,
+						int line)
+{
+	//printk("%s:%d:%.*s: setting bit %d\n", file, line,
+	//     res->lockname.len, res->lockname.name, bit);
+	set_bit(bit, res->refmap);
+}
+
+static inline void __dlm_lockres_clear_refmap_bit(int bit,
+						  struct dlm_lock_resource *res,
+						  const char *file,
+						  int line)
+{
+	//printk("%s:%d:%.*s: clearing bit %d\n", file, line,
+	//     res->lockname.len, res->lockname.name, bit);
+	clear_bit(bit, res->refmap);
+}
+
+void __dlm_lockres_drop_inflight_ref(struct dlm_ctxt *dlm,
+				   struct dlm_lock_resource *res,
+				   const char *file,
+				   int line);
+void __dlm_lockres_grab_inflight_ref(struct dlm_ctxt *dlm,
+				   struct dlm_lock_resource *res,
+				   int new_lockres,
+				   const char *file,
+				   int line);
+#define dlm_lockres_drop_inflight_ref(d,r)  \
+	__dlm_lockres_drop_inflight_ref(d,r,__FILE__,__LINE__)
+#define dlm_lockres_grab_inflight_ref(d,r)  \
+	__dlm_lockres_grab_inflight_ref(d,r,0,__FILE__,__LINE__)
+#define dlm_lockres_grab_inflight_ref_new(d,r)  \
+	__dlm_lockres_grab_inflight_ref(d,r,1,__FILE__,__LINE__)
+
 void dlm_queue_ast(struct dlm_ctxt *dlm, struct dlm_lock *lock);
 void dlm_queue_bast(struct dlm_ctxt *dlm, struct dlm_lock *lock);
 void dlm_do_local_ast(struct dlm_ctxt *dlm,
@@ -805,6 +868,7 @@ int dlm_lockres_is_dirty(struct dlm_ctxt *dlm, struct dlm_lock_resource *res);
 int dlm_migrate_lockres(struct dlm_ctxt *dlm,
 			struct dlm_lock_resource *res,
 			u8 target);
+int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res);
 int dlm_finish_migration(struct dlm_ctxt *dlm,
 			 struct dlm_lock_resource *res,
 			 u8 old_master);
@@ -814,6 +878,7 @@ void __dlm_lockres_reserve_ast(struct dlm_lock_resource *res);
 
 int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data);
 int dlm_assert_master_handler(struct o2net_msg *msg, u32 len, void *data);
+int dlm_deref_lockres_handler(struct o2net_msg *msg, u32 len, void *data);
 int dlm_migrate_request_handler(struct o2net_msg *msg, u32 len, void *data);
 int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data);
 int dlm_master_requery_handler(struct o2net_msg *msg, u32 len, void *data);
@@ -856,10 +921,12 @@ static inline void __dlm_wait_on_lockres(struct dlm_lock_resource *res)
 int dlm_init_mle_cache(void);
 void dlm_destroy_mle_cache(void);
 void dlm_hb_event_notify_attached(struct dlm_ctxt *dlm, int idx, int node_up);
+int dlm_drop_lockres_ref(struct dlm_ctxt *dlm,
+			 struct dlm_lock_resource *res);
 void dlm_clean_master_list(struct dlm_ctxt *dlm,
 			   u8 dead_node);
 int dlm_lock_basts_flushed(struct dlm_ctxt *dlm, struct dlm_lock *lock);
-
+int __dlm_lockres_has_locks(struct dlm_lock_resource *res);
 int __dlm_lockres_unused(struct dlm_lock_resource *res);
 
 static inline const char * dlm_lock_mode_name(int mode)
diff --git a/fs/ocfs2/dlm/dlmdebug.c b/fs/ocfs2/dlm/dlmdebug.c
index 3f6c8d88f7af..1015cc7bf9cb 100644
--- a/fs/ocfs2/dlm/dlmdebug.c
+++ b/fs/ocfs2/dlm/dlmdebug.c
@@ -53,6 +53,23 @@ void dlm_print_one_lock_resource(struct dlm_lock_resource *res)
 	spin_unlock(&res->spinlock);
 }
 
+static void dlm_print_lockres_refmap(struct dlm_lock_resource *res)
+{
+	int bit;
+	assert_spin_locked(&res->spinlock);
+
+	mlog(ML_NOTICE, "  refmap nodes: [ ");
+	bit = 0;
+	while (1) {
+		bit = find_next_bit(res->refmap, O2NM_MAX_NODES, bit);
+		if (bit >= O2NM_MAX_NODES)
+			break;
+		printk("%u ", bit);
+		bit++;
+	}
+	printk("], inflight=%u\n", res->inflight_locks);
+}
+
 void __dlm_print_one_lock_resource(struct dlm_lock_resource *res)
 {
 	struct list_head *iter2;
@@ -65,6 +82,7 @@ void __dlm_print_one_lock_resource(struct dlm_lock_resource *res)
 	       res->owner, res->state);
 	mlog(ML_NOTICE, "  last used: %lu, on purge list: %s\n",
 	     res->last_used, list_empty(&res->purge) ? "no" : "yes");
+	dlm_print_lockres_refmap(res);
 	mlog(ML_NOTICE, "  granted queue: \n");
 	list_for_each(iter2, &res->granted) {
 		lock = list_entry(iter2, struct dlm_lock, list);
diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
index f0b25f2dd205..3995de360264 100644
--- a/fs/ocfs2/dlm/dlmdomain.c
+++ b/fs/ocfs2/dlm/dlmdomain.c
@@ -125,10 +125,10 @@ void __dlm_insert_lockres(struct dlm_ctxt *dlm,
 	hlist_add_head(&res->hash_node, bucket);
 }
 
-struct dlm_lock_resource * __dlm_lookup_lockres(struct dlm_ctxt *dlm,
-						const char *name,
-						unsigned int len,
-						unsigned int hash)
+struct dlm_lock_resource * __dlm_lookup_lockres_full(struct dlm_ctxt *dlm,
+						     const char *name,
+						     unsigned int len,
+						     unsigned int hash)
 {
 	struct hlist_head *bucket;
 	struct hlist_node *list;
@@ -154,6 +154,37 @@ struct dlm_lock_resource * __dlm_lookup_lockres(struct dlm_ctxt *dlm,
 	return NULL;
 }
 
+/* intended to be called by functions which do not care about lock
+ * resources which are being purged (most net _handler functions).
+ * this will return NULL for any lock resource which is found but
+ * currently in the process of dropping its mastery reference.
+ * use __dlm_lookup_lockres_full when you need the lock resource
+ * regardless (e.g. dlm_get_lock_resource) */
+struct dlm_lock_resource * __dlm_lookup_lockres(struct dlm_ctxt *dlm,
+						const char *name,
+						unsigned int len,
+						unsigned int hash)
+{
+	struct dlm_lock_resource *res = NULL;
+
+	mlog_entry("%.*s\n", len, name);
+
+	assert_spin_locked(&dlm->spinlock);
+
+	res = __dlm_lookup_lockres_full(dlm, name, len, hash);
+	if (res) {
+		spin_lock(&res->spinlock);
+		if (res->state & DLM_LOCK_RES_DROPPING_REF) {
+			spin_unlock(&res->spinlock);
+			dlm_lockres_put(res);
+			return NULL;
+		}
+		spin_unlock(&res->spinlock);
+	}
+
+	return res;
+}
+
 struct dlm_lock_resource * dlm_lookup_lockres(struct dlm_ctxt *dlm,
 				    const char *name,
 				    unsigned int len)
@@ -330,43 +361,60 @@ static void dlm_complete_dlm_shutdown(struct dlm_ctxt *dlm)
 	wake_up(&dlm_domain_events);
 }
 
-static void dlm_migrate_all_locks(struct dlm_ctxt *dlm)
+static int dlm_migrate_all_locks(struct dlm_ctxt *dlm)
 {
-	int i;
+	int i, num, n, ret = 0;
 	struct dlm_lock_resource *res;
+	struct hlist_node *iter;
+	struct hlist_head *bucket;
+	int dropped;
 
 	mlog(0, "Migrating locks from domain %s\n", dlm->name);
-restart:
+
+	num = 0;
 	spin_lock(&dlm->spinlock);
 	for (i = 0; i < DLM_HASH_BUCKETS; i++) {
-		while (!hlist_empty(dlm_lockres_hash(dlm, i))) {
-			res = hlist_entry(dlm_lockres_hash(dlm, i)->first,
-					  struct dlm_lock_resource, hash_node);
-			/* need reference when manually grabbing lockres */
+redo_bucket:
+		n = 0;
+		bucket = dlm_lockres_hash(dlm, i);
+		iter = bucket->first;
+		while (iter) {
+			n++;
+			res = hlist_entry(iter, struct dlm_lock_resource,
+					  hash_node);
 			dlm_lockres_get(res);
-			/* this should unhash the lockres
-			 * and exit with dlm->spinlock */
-			mlog(0, "purging res=%p\n", res);
-			if (dlm_lockres_is_dirty(dlm, res)) {
-				/* HACK!  this should absolutely go.
-				 * need to figure out why some empty
-				 * lockreses are still marked dirty */
-				mlog(ML_ERROR, "lockres %.*s dirty!\n",
-				     res->lockname.len, res->lockname.name);
-
-				spin_unlock(&dlm->spinlock);
-				dlm_kick_thread(dlm, res);
-				wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
-				dlm_lockres_put(res);
-				goto restart;
-			}
-			dlm_purge_lockres(dlm, res);
+			/* migrate, if necessary.  this will drop the dlm
+			 * spinlock and retake it if it does migration. */
+			dropped = dlm_empty_lockres(dlm, res);
+
+			spin_lock(&res->spinlock);
+			__dlm_lockres_calc_usage(dlm, res);
+			iter = res->hash_node.next;
+			spin_unlock(&res->spinlock);
+
 			dlm_lockres_put(res);
+
+			cond_resched_lock(&dlm->spinlock);
+
+			if (dropped)
+				goto redo_bucket;
 		}
+		num += n;
+		mlog(0, "%s: touched %d lockreses in bucket %d "
+		     "(tot=%d)\n", dlm->name, n, i, num);
 	}
 	spin_unlock(&dlm->spinlock);
-
+	wake_up(&dlm->dlm_thread_wq);
+
+	/* let the dlm thread take care of purging, keep scanning until
+	 * nothing remains in the hash */
+	if (num) {
+		mlog(0, "%s: %d lock resources in hash last pass\n",
+		     dlm->name, num);
+		ret = -EAGAIN;
+	}
 	mlog(0, "DONE Migrating locks from domain %s\n", dlm->name);
+	return ret;
 }
 
 static int dlm_no_joining_node(struct dlm_ctxt *dlm)
@@ -571,7 +619,9 @@ void dlm_unregister_domain(struct dlm_ctxt *dlm)
 		/* We changed dlm state, notify the thread */
 		dlm_kick_thread(dlm, NULL);
 
-		dlm_migrate_all_locks(dlm);
+		while (dlm_migrate_all_locks(dlm)) {
+			mlog(0, "%s: more migration to do\n", dlm->name);
+		}
 		dlm_mark_domain_leaving(dlm);
 		dlm_leave_domain(dlm);
 		dlm_complete_dlm_shutdown(dlm);
@@ -1082,6 +1132,13 @@ static int dlm_register_domain_handlers(struct dlm_ctxt *dlm)
 	if (status)
 		goto bail;
 
+	status = o2net_register_handler(DLM_DEREF_LOCKRES_MSG, dlm->key,
+					sizeof(struct dlm_deref_lockres),
+					dlm_deref_lockres_handler,
+					dlm, &dlm->dlm_domain_handlers);
+	if (status)
+		goto bail;
+
 	status = o2net_register_handler(DLM_MIGRATE_REQUEST_MSG, dlm->key,
 					sizeof(struct dlm_migrate_request),
 					dlm_migrate_request_handler,
diff --git a/fs/ocfs2/dlm/dlmlock.c b/fs/ocfs2/dlm/dlmlock.c
index e5ca3db197f6..ac91a76b1e78 100644
--- a/fs/ocfs2/dlm/dlmlock.c
+++ b/fs/ocfs2/dlm/dlmlock.c
@@ -163,6 +163,10 @@ static enum dlm_status dlmlock_master(struct dlm_ctxt *dlm,
 			kick_thread = 1;
 		}
 	}
+	/* reduce the inflight count, this may result in the lockres
+	 * being purged below during calc_usage */
+	if (lock->ml.node == dlm->node_num)
+		dlm_lockres_drop_inflight_ref(dlm, res);
 
 	spin_unlock(&res->spinlock);
 	wake_up(&res->wq);
diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 0ad872055cb3..4645ec2e0fc3 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -99,9 +99,9 @@ static void dlm_mle_node_up(struct dlm_ctxt *dlm,
 			    int idx);
 
 static void dlm_assert_master_worker(struct dlm_work_item *item, void *data);
-static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
-				unsigned int namelen, void *nodemap,
-				u32 flags);
+static int dlm_do_assert_master(struct dlm_ctxt *dlm,
+				struct dlm_lock_resource *res,
+				void *nodemap, u32 flags);
 
 static inline int dlm_mle_equal(struct dlm_ctxt *dlm,
 				struct dlm_master_list_entry *mle,
@@ -237,7 +237,8 @@ static int dlm_find_mle(struct dlm_ctxt *dlm,
 			struct dlm_master_list_entry **mle,
 			char *name, unsigned int namelen);
 
-static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to);
+static int dlm_do_master_request(struct dlm_lock_resource *res,
+				 struct dlm_master_list_entry *mle, int to);
 
 
 static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
@@ -687,6 +688,7 @@ static void dlm_init_lockres(struct dlm_ctxt *dlm,
 	INIT_LIST_HEAD(&res->purge);
 	atomic_set(&res->asts_reserved, 0);
 	res->migration_pending = 0;
+	res->inflight_locks = 0;
 
 	kref_init(&res->refs);
 
@@ -700,6 +702,7 @@ static void dlm_init_lockres(struct dlm_ctxt *dlm,
 	res->last_used = 0;
 
 	memset(res->lvb, 0, DLM_LVB_LEN);
+	memset(res->refmap, 0, sizeof(res->refmap));
 }
 
 struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
@@ -722,6 +725,42 @@ struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
 	return res;
 }
 
+void __dlm_lockres_grab_inflight_ref(struct dlm_ctxt *dlm,
+				   struct dlm_lock_resource *res,
+				   int new_lockres,
+				   const char *file,
+				   int line)
+{
+	if (!new_lockres)
+		assert_spin_locked(&res->spinlock);
+
+	if (!test_bit(dlm->node_num, res->refmap)) {
+		BUG_ON(res->inflight_locks != 0);
+		dlm_lockres_set_refmap_bit(dlm->node_num, res);
+	}
+	res->inflight_locks++;
+	mlog(0, "%s:%.*s: inflight++: now %u\n",
+	     dlm->name, res->lockname.len, res->lockname.name,
+	     res->inflight_locks);
+}
+
+void __dlm_lockres_drop_inflight_ref(struct dlm_ctxt *dlm,
+				   struct dlm_lock_resource *res,
+				   const char *file,
+				   int line)
+{
+	assert_spin_locked(&res->spinlock);
+
+	BUG_ON(res->inflight_locks == 0);
+	res->inflight_locks--;
+	mlog(0, "%s:%.*s: inflight--: now %u\n",
+	     dlm->name, res->lockname.len, res->lockname.name,
+	     res->inflight_locks);
+	if (res->inflight_locks == 0)
+		dlm_lockres_clear_refmap_bit(dlm->node_num, res);
+	wake_up(&res->wq);
+}
+
 /*
  * lookup a lock resource by name.
  * may already exist in the hashtable.
@@ -752,6 +791,7 @@ struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
 	unsigned int hash;
 	int tries = 0;
 	int bit, wait_on_recovery = 0;
+	int drop_inflight_if_nonlocal = 0;
 
 	BUG_ON(!lockid);
 
@@ -761,9 +801,30 @@ struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
 
 lookup:
 	spin_lock(&dlm->spinlock);
-	tmpres = __dlm_lookup_lockres(dlm, lockid, namelen, hash);
+	tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
 	if (tmpres) {
+		int dropping_ref = 0;
+
+		spin_lock(&tmpres->spinlock);
+		if (tmpres->owner == dlm->node_num) {
+			BUG_ON(tmpres->state & DLM_LOCK_RES_DROPPING_REF);
+			dlm_lockres_grab_inflight_ref(dlm, tmpres);
+		} else if (tmpres->state & DLM_LOCK_RES_DROPPING_REF)
+			dropping_ref = 1;
+		spin_unlock(&tmpres->spinlock);
 		spin_unlock(&dlm->spinlock);
+
+		/* wait until done messaging the master, drop our ref to allow
+		 * the lockres to be purged, start over. */
+		if (dropping_ref) {
+			spin_lock(&tmpres->spinlock);
+			__dlm_wait_on_lockres_flags(tmpres, DLM_LOCK_RES_DROPPING_REF);
+			spin_unlock(&tmpres->spinlock);
+			dlm_lockres_put(tmpres);
+			tmpres = NULL;
+			goto lookup;
+		}
+
 		mlog(0, "found in hash!\n");
 		if (res)
 			dlm_lockres_put(res);
@@ -793,6 +854,7 @@ lookup:
 		spin_lock(&res->spinlock);
 		dlm_change_lockres_owner(dlm, res, dlm->node_num);
 		__dlm_insert_lockres(dlm, res);
+		dlm_lockres_grab_inflight_ref(dlm, res);
 		spin_unlock(&res->spinlock);
 		spin_unlock(&dlm->spinlock);
 		/* lockres still marked IN_PROGRESS */
@@ -805,29 +867,40 @@ lookup:
 	/* if we found a block, wait for lock to be mastered by another node */
 	blocked = dlm_find_mle(dlm, &mle, (char *)lockid, namelen);
 	if (blocked) {
+		int mig;
 		if (mle->type == DLM_MLE_MASTER) {
 			mlog(ML_ERROR, "master entry for nonexistent lock!\n");
 			BUG();
-		} else if (mle->type == DLM_MLE_MIGRATION) {
-			/* migration is in progress! */
-			/* the good news is that we now know the
-			 * "current" master (mle->master). */
-
+		}
+		mig = (mle->type == DLM_MLE_MIGRATION);
+		/* if there is a migration in progress, let the migration
+		 * finish before continuing.  we can wait for the absence
+		 * of the MIGRATION mle: either the migrate finished or
+		 * one of the nodes died and the mle was cleaned up.
+		 * if there is a BLOCK here, but it already has a master
+		 * set, we are too late.  the master does not have a ref
+		 * for us in the refmap.  detach the mle and drop it.
+		 * either way, go back to the top and start over. */
+		if (mig || mle->master != O2NM_MAX_NODES) {
+			BUG_ON(mig && mle->master == dlm->node_num);
+			/* we arrived too late.  the master does not
+			 * have a ref for us. retry. */
+			mlog(0, "%s:%.*s: late on %s\n",
+			     dlm->name, namelen, lockid,
+			     mig ?  "MIGRATION" : "BLOCK");
 			spin_unlock(&dlm->master_lock);
-			assert_spin_locked(&dlm->spinlock);
-
-			/* set the lockres owner and hash it */
-			spin_lock(&res->spinlock);
-			dlm_set_lockres_owner(dlm, res, mle->master);
-			__dlm_insert_lockres(dlm, res);
-			spin_unlock(&res->spinlock);
 			spin_unlock(&dlm->spinlock);
 
 			/* master is known, detach */
-			dlm_mle_detach_hb_events(dlm, mle);
+			if (!mig)
+				dlm_mle_detach_hb_events(dlm, mle);
 			dlm_put_mle(mle);
 			mle = NULL;
-			goto wake_waiters;
+			/* this is lame, but we cant wait on either
+			 * the mle or lockres waitqueue here */
+			if (mig)
+				msleep(100);
+			goto lookup;
 		}
 	} else {
 		/* go ahead and try to master lock on this node */
@@ -858,6 +931,13 @@ lookup:
 
 	/* finally add the lockres to its hash bucket */
 	__dlm_insert_lockres(dlm, res);
+	/* since this lockres is new it doesnt not require the spinlock */
+	dlm_lockres_grab_inflight_ref_new(dlm, res);
+
+	/* if this node does not become the master make sure to drop
+	 * this inflight reference below */
+	drop_inflight_if_nonlocal = 1;
+
 	/* get an extra ref on the mle in case this is a BLOCK
 	 * if so, the creator of the BLOCK may try to put the last
 	 * ref at this time in the assert master handler, so we
@@ -910,7 +990,7 @@ redo_request:
 	ret = -EINVAL;
 	dlm_node_iter_init(mle->vote_map, &iter);
 	while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
-		ret = dlm_do_master_request(mle, nodenum);
+		ret = dlm_do_master_request(res, mle, nodenum);
 		if (ret < 0)
 			mlog_errno(ret);
 		if (mle->master != O2NM_MAX_NODES) {
@@ -960,6 +1040,8 @@ wait:
 
 wake_waiters:
 	spin_lock(&res->spinlock);
+	if (res->owner != dlm->node_num && drop_inflight_if_nonlocal)
+		dlm_lockres_drop_inflight_ref(dlm, res);
 	res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
 	spin_unlock(&res->spinlock);
 	wake_up(&res->wq);
@@ -998,7 +1080,7 @@ recheck:
 		/* this will cause the master to re-assert across
 		 * the whole cluster, freeing up mles */
 		if (res->owner != dlm->node_num) {
-			ret = dlm_do_master_request(mle, res->owner);
+			ret = dlm_do_master_request(res, mle, res->owner);
 			if (ret < 0) {
 				/* give recovery a chance to run */
 				mlog(ML_ERROR, "link to %u went down?: %d\n", res->owner, ret);
@@ -1062,6 +1144,8 @@ recheck:
 			 	 * now tell other nodes that I am
 				 * mastering this. */
 				mle->master = dlm->node_num;
+				/* ref was grabbed in get_lock_resource
+				 * will be dropped in dlmlock_master */
 				assert = 1;
 				sleep = 0;
 			}
@@ -1087,7 +1171,8 @@ recheck:
 					 (atomic_read(&mle->woken) == 1),
 					 timeo);
 		if (res->owner == O2NM_MAX_NODES) {
-			mlog(0, "waiting again\n");
+			mlog(0, "%s:%.*s: waiting again\n", dlm->name,
+			     res->lockname.len, res->lockname.name);
 			goto recheck;
 		}
 		mlog(0, "done waiting, master is %u\n", res->owner);
@@ -1100,8 +1185,7 @@ recheck:
 		m = dlm->node_num;
 		mlog(0, "about to master %.*s here, this=%u\n",
 		     res->lockname.len, res->lockname.name, m);
-		ret = dlm_do_assert_master(dlm, res->lockname.name,
-					   res->lockname.len, mle->vote_map, 0);
+		ret = dlm_do_assert_master(dlm, res, mle->vote_map, 0);
 		if (ret) {
 			/* This is a failure in the network path,
 			 * not in the response to the assert_master
@@ -1117,6 +1201,8 @@ recheck:
 
 	/* set the lockres owner */
 	spin_lock(&res->spinlock);
+	/* mastery reference obtained either during
+	 * assert_master_handler or in get_lock_resource */
 	dlm_change_lockres_owner(dlm, res, m);
 	spin_unlock(&res->spinlock);
 
@@ -1283,7 +1369,8 @@ static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
  *
  */
 
-static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to)
+static int dlm_do_master_request(struct dlm_lock_resource *res,
+				 struct dlm_master_list_entry *mle, int to)
 {
 	struct dlm_ctxt *dlm = mle->dlm;
 	struct dlm_master_request request;
@@ -1339,6 +1426,9 @@ again:
 		case DLM_MASTER_RESP_YES:
 			set_bit(to, mle->response_map);
 			mlog(0, "node %u is the master, response=YES\n", to);
+			mlog(0, "%s:%.*s: master node %u now knows I have a "
+			     "reference\n", dlm->name, res->lockname.len,
+			     res->lockname.name, to);
 			mle->master = to;
 			break;
 		case DLM_MASTER_RESP_NO:
@@ -1428,8 +1518,10 @@ way_up_top:
 		}
 
 		if (res->owner == dlm->node_num) {
+			mlog(0, "%s:%.*s: setting bit %u in refmap\n",
+			     dlm->name, namelen, name, request->node_idx);
+			dlm_lockres_set_refmap_bit(request->node_idx, res);
 			spin_unlock(&res->spinlock);
-			// mlog(0, "this node is the master\n");
 			response = DLM_MASTER_RESP_YES;
 			if (mle)
 				kmem_cache_free(dlm_mle_cache, mle);
@@ -1477,7 +1569,6 @@ way_up_top:
 			mlog(0, "node %u is master, but trying to migrate to "
 			     "node %u.\n", tmpmle->master, tmpmle->new_master);
 			if (tmpmle->master == dlm->node_num) {
-				response = DLM_MASTER_RESP_YES;
 				mlog(ML_ERROR, "no owner on lockres, but this "
 				     "node is trying to migrate it to %u?!\n",
 				     tmpmle->new_master);
@@ -1494,6 +1585,10 @@ way_up_top:
 				 * go back and clean the mles on any
 				 * other nodes */
 				dispatch_assert = 1;
+				dlm_lockres_set_refmap_bit(request->node_idx, res);
+				mlog(0, "%s:%.*s: setting bit %u in refmap\n",
+				     dlm->name, namelen, name,
+				     request->node_idx);
 			} else
 				response = DLM_MASTER_RESP_NO;
 		} else {
@@ -1607,15 +1702,17 @@ send_response:
  * can periodically run all locks owned by this node
  * and re-assert across the cluster...
  */
-static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
-				unsigned int namelen, void *nodemap,
-				u32 flags)
+int dlm_do_assert_master(struct dlm_ctxt *dlm,
+			 struct dlm_lock_resource *res,
+			 void *nodemap, u32 flags)
 {
 	struct dlm_assert_master assert;
 	int to, tmpret;
 	struct dlm_node_iter iter;
 	int ret = 0;
 	int reassert;
+	const char *lockname = res->lockname.name;
+	unsigned int namelen = res->lockname.len;
 
 	BUG_ON(namelen > O2NM_MAX_NAME_LEN);
 again:
@@ -1647,6 +1744,7 @@ again:
 			mlog(0, "link to %d went down!\n", to);
 			/* any nonzero status return will do */
 			ret = tmpret;
+			r = 0;
 		} else if (r < 0) {
 			/* ok, something horribly messed.  kill thyself. */
 			mlog(ML_ERROR,"during assert master of %.*s to %u, "
@@ -1661,12 +1759,29 @@ again:
 			spin_unlock(&dlm->master_lock);
 			spin_unlock(&dlm->spinlock);
 			BUG();
-		} else if (r == EAGAIN) {
+		}
+
+		if (r & DLM_ASSERT_RESPONSE_REASSERT &&
+		    !(r & DLM_ASSERT_RESPONSE_MASTERY_REF)) {
+				mlog(ML_ERROR, "%.*s: very strange, "
+				     "master MLE but no lockres on %u\n",
+				     namelen, lockname, to);
+		}
+
+		if (r & DLM_ASSERT_RESPONSE_REASSERT) {
 			mlog(0, "%.*s: node %u create mles on other "
 			     "nodes and requests a re-assert\n", 
 			     namelen, lockname, to);
 			reassert = 1;
 		}
+		if (r & DLM_ASSERT_RESPONSE_MASTERY_REF) {
+			mlog(0, "%.*s: node %u has a reference to this "
+			     "lockres, set the bit in the refmap\n",
+			     namelen, lockname, to);
+			spin_lock(&res->spinlock);
+			dlm_lockres_set_refmap_bit(to, res);
+			spin_unlock(&res->spinlock);
+		}
 	}
 
 	if (reassert)
@@ -1693,7 +1808,7 @@ int dlm_assert_master_handler(struct o2net_msg *msg, u32 len, void *data)
 	char *name;
 	unsigned int namelen, hash;
 	u32 flags;
-	int master_request = 0;
+	int master_request = 0, have_lockres_ref = 0;
 	int ret = 0;
 
 	if (!dlm_grab(dlm))
@@ -1864,6 +1979,7 @@ ok:
 				dlm_change_lockres_owner(dlm, res, mle->master);
 			}
 			spin_unlock(&res->spinlock);
+			have_lockres_ref = 1;
 		}
 
 		/* master is known, detach if not already detached.
@@ -1918,7 +2034,19 @@ done:
 	dlm_put(dlm);
 	if (master_request) {
 		mlog(0, "need to tell master to reassert\n");
-		ret = EAGAIN;  // positive. negative would shoot down the node.
+		/* positive. negative would shoot down the node. */
+		ret |= DLM_ASSERT_RESPONSE_REASSERT;
+		if (!have_lockres_ref) {
+			mlog(ML_ERROR, "strange, got assert from %u, MASTER "
+			     "mle present here for %s:%.*s, but no lockres!\n",
+			     assert->node_idx, dlm->name, namelen, name);
+		}
+	}
+	if (have_lockres_ref) {
+		/* let the master know we have a reference to the lockres */
+		ret |= DLM_ASSERT_RESPONSE_MASTERY_REF;
+		mlog(0, "%s:%.*s: got assert from %u, need a ref\n",
+		     dlm->name, namelen, name, assert->node_idx);
 	}
 	return ret;
 
@@ -2023,9 +2151,7 @@ static void dlm_assert_master_worker(struct dlm_work_item *item, void *data)
 	 * even if one or more nodes die */
 	mlog(0, "worker about to master %.*s here, this=%u\n",
 		     res->lockname.len, res->lockname.name, dlm->node_num);
-	ret = dlm_do_assert_master(dlm, res->lockname.name,
-				   res->lockname.len,
-				   nodemap, flags);
+	ret = dlm_do_assert_master(dlm, res, nodemap, flags);
 	if (ret < 0) {
 		/* no need to restart, we are done */
 		if (!dlm_is_host_down(ret))
@@ -2097,6 +2223,104 @@ static int dlm_pre_master_reco_lockres(struct dlm_ctxt *dlm,
 	return ret;
 }
 
+/*
+ * DLM_DEREF_LOCKRES_MSG
+ */
+
+int dlm_drop_lockres_ref(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
+{
+	struct dlm_deref_lockres deref;
+	int ret = 0, r;
+	const char *lockname;
+	unsigned int namelen;
+
+	lockname = res->lockname.name;
+	namelen = res->lockname.len;
+	BUG_ON(namelen > O2NM_MAX_NAME_LEN);
+
+	mlog(0, "%s:%.*s: sending deref to %d\n",
+	     dlm->name, namelen, lockname, res->owner);
+	memset(&deref, 0, sizeof(deref));
+	deref.node_idx = dlm->node_num;
+	deref.namelen = namelen;
+	memcpy(deref.name, lockname, namelen);
+
+	ret = o2net_send_message(DLM_DEREF_LOCKRES_MSG, dlm->key,
+				 &deref, sizeof(deref), res->owner, &r);
+	if (ret < 0)
+		mlog_errno(ret);
+	else if (r < 0) {
+		/* BAD.  other node says I did not have a ref. */
+		mlog(ML_ERROR,"while dropping ref on %s:%.*s "
+		    "(master=%u) got %d.\n", dlm->name, namelen,
+		    lockname, res->owner, r);
+		dlm_print_one_lock_resource(res);
+		BUG();
+	}
+	return ret;
+}
+
+int dlm_deref_lockres_handler(struct o2net_msg *msg, u32 len, void *data)
+{
+	struct dlm_ctxt *dlm = data;
+	struct dlm_deref_lockres *deref = (struct dlm_deref_lockres *)msg->buf;
+	struct dlm_lock_resource *res = NULL;
+	char *name;
+	unsigned int namelen;
+	int ret = -EINVAL;
+	u8 node;
+	unsigned int hash;
+
+	if (!dlm_grab(dlm))
+		return 0;
+
+	name = deref->name;
+	namelen = deref->namelen;
+	node = deref->node_idx;
+
+	if (namelen > DLM_LOCKID_NAME_MAX) {
+		mlog(ML_ERROR, "Invalid name length!");
+		goto done;
+	}
+	if (deref->node_idx >= O2NM_MAX_NODES) {
+		mlog(ML_ERROR, "Invalid node number: %u\n", node);
+		goto done;
+	}
+
+	hash = dlm_lockid_hash(name, namelen);
+
+	spin_lock(&dlm->spinlock);
+	res = __dlm_lookup_lockres_full(dlm, name, namelen, hash);
+	if (!res) {
+		spin_unlock(&dlm->spinlock);
+		mlog(ML_ERROR, "%s:%.*s: bad lockres name\n",
+		     dlm->name, namelen, name);
+		goto done;
+	}
+	spin_unlock(&dlm->spinlock);
+
+	spin_lock(&res->spinlock);
+	BUG_ON(res->state & DLM_LOCK_RES_DROPPING_REF);
+	if (test_bit(node, res->refmap)) {
+		ret = 0;
+		dlm_lockres_clear_refmap_bit(node, res);
+	} else {
+		mlog(ML_ERROR, "%s:%.*s: node %u trying to drop ref "
+		     "but it is already dropped!\n", dlm->name, namelen,
+		     name, node);
+		__dlm_print_one_lock_resource(res);
+	}
+	spin_unlock(&res->spinlock);
+
+	if (!ret)
+		dlm_lockres_calc_usage(dlm, res);
+done:
+	if (res)
+		dlm_lockres_put(res);
+	dlm_put(dlm);
+	return ret;
+}
+
 
 /*
  * DLM_MIGRATE_LOCKRES
@@ -2376,6 +2600,53 @@ leave:
 	return ret;
 }
 
+#define DLM_MIGRATION_RETRY_MS  100
+
+/* Should be called only after beginning the domain leave process.
+ * There should not be any remaining locks on nonlocal lock resources,
+ * and there should be no local locks left on locally mastered resources.
+ *
+ * Called with the dlm spinlock held, may drop it to do migration, but
+ * will re-acquire before exit.
+ *
+ * Returns: 1 if dlm->spinlock was dropped/retaken, 0 if never dropped */
+int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
+{
+	int ret;
+	int lock_dropped = 0;
+
+	if (res->owner != dlm->node_num) {
+		if (!__dlm_lockres_unused(res)) {
+			mlog(ML_ERROR, "%s:%.*s: this node is not master, "
+			     "trying to free this but locks remain\n",
+			     dlm->name, res->lockname.len, res->lockname.name);
+		}
+		goto leave;
+	}
+
+	/* Wheee! Migrate lockres here! Will sleep so drop spinlock. */
+	spin_unlock(&dlm->spinlock);
+	lock_dropped = 1;
+	while (1) {
+		ret = dlm_migrate_lockres(dlm, res, O2NM_MAX_NODES);
+		if (ret >= 0)
+			break;
+		if (ret == -ENOTEMPTY) {
+			mlog(ML_ERROR, "lockres %.*s still has local locks!\n",
+		     		res->lockname.len, res->lockname.name);
+			BUG();
+		}
+
+		mlog(0, "lockres %.*s: migrate failed, "
+		     "retrying\n", res->lockname.len,
+		     res->lockname.name);
+		msleep(DLM_MIGRATION_RETRY_MS);
+	}
+	spin_lock(&dlm->spinlock);
+leave:
+	return lock_dropped;
+}
+
 int dlm_lock_basts_flushed(struct dlm_ctxt *dlm, struct dlm_lock *lock)
 {
 	int ret;
@@ -2490,7 +2761,7 @@ static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
 {
 	struct list_head *iter, *iter2;
 	struct list_head *queue = &res->granted;
-	int i;
+	int i, bit;
 	struct dlm_lock *lock;
 
 	assert_spin_locked(&res->spinlock);
@@ -2508,12 +2779,28 @@ static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
 				BUG_ON(!list_empty(&lock->bast_list));
 				BUG_ON(lock->ast_pending);
 				BUG_ON(lock->bast_pending);
+				dlm_lockres_clear_refmap_bit(lock->ml.node, res);
 				list_del_init(&lock->list);
 				dlm_lock_put(lock);
 			}
 		}
 		queue++;
 	}
+	bit = 0;
+	while (1) {
+		bit = find_next_bit(res->refmap, O2NM_MAX_NODES, bit);
+		if (bit >= O2NM_MAX_NODES)
+			break;
+		/* do not clear the local node reference, if there is a
+		 * process holding this, let it drop the ref itself */
+		if (bit != dlm->node_num) {
+			mlog(0, "%s:%.*s: node %u had a ref to this "
+			     "migrating lockres, clearing\n", dlm->name,
+			     res->lockname.len, res->lockname.name, bit);
+			dlm_lockres_clear_refmap_bit(bit, res);
+		}
+		bit++;
+	}
 }
 
 /* for now this is not too intelligent.  we will
@@ -2601,6 +2888,16 @@ static int dlm_do_migrate_request(struct dlm_ctxt *dlm,
 			mlog(0, "migrate request (node %u) returned %d!\n",
 			     nodenum, status);
 			ret = status;
+		} else if (status == DLM_MIGRATE_RESPONSE_MASTERY_REF) {
+			/* during the migration request we short-circuited
+			 * the mastery of the lockres.  make sure we have
+			 * a mastery ref for nodenum */
+			mlog(0, "%s:%.*s: need ref for node %u\n",
+			     dlm->name, res->lockname.len, res->lockname.name,
+			     nodenum);
+			spin_lock(&res->spinlock);
+			dlm_lockres_set_refmap_bit(nodenum, res);
+			spin_unlock(&res->spinlock);
 		}
 	}
 
@@ -2745,7 +3042,13 @@ static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
 			/* remove it from the list so that only one
 			 * mle will be found */
 			list_del_init(&tmp->list);
-			__dlm_mle_detach_hb_events(dlm, mle);
+			/* this was obviously WRONG.  mle is uninited here.  should be tmp. */
+			__dlm_mle_detach_hb_events(dlm, tmp);
+			ret = DLM_MIGRATE_RESPONSE_MASTERY_REF;
+			mlog(0, "%s:%.*s: master=%u, newmaster=%u, "
+			    "telling master to get ref for cleared out mle "
+			    "during migration\n", dlm->name, namelen, name,
+			    master, new_master);
 		}
 		spin_unlock(&tmp->spinlock);
 	}
@@ -2753,6 +3056,8 @@ static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
 	/* now add a migration mle to the tail of the list */
 	dlm_init_mle(mle, DLM_MLE_MIGRATION, dlm, res, name, namelen);
 	mle->new_master = new_master;
+	/* the new master will be sending an assert master for this.
+	 * at that point we will get the refmap reference */
 	mle->master = master;
 	/* do this for consistency with other mle types */
 	set_bit(new_master, mle->maybe_map);
@@ -2902,6 +3207,13 @@ int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
 	clear_bit(dlm->node_num, iter.node_map);
 	spin_unlock(&dlm->spinlock);
 
+	/* ownership of the lockres is changing.  account for the
+	 * mastery reference here since old_master will briefly have
+	 * a reference after the migration completes */
+	spin_lock(&res->spinlock);
+	dlm_lockres_set_refmap_bit(old_master, res);
+	spin_unlock(&res->spinlock);
+
 	mlog(0, "now time to do a migrate request to other nodes\n");
 	ret = dlm_do_migrate_request(dlm, res, old_master,
 				     dlm->node_num, &iter);
@@ -2914,8 +3226,7 @@ int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
 	     res->lockname.len, res->lockname.name);
 	/* this call now finishes out the nodemap
 	 * even if one or more nodes die */
-	ret = dlm_do_assert_master(dlm, res->lockname.name,
-				   res->lockname.len, iter.node_map,
+	ret = dlm_do_assert_master(dlm, res, iter.node_map,
 				   DLM_ASSERT_MASTER_FINISH_MIGRATION);
 	if (ret < 0) {
 		/* no longer need to retry.  all living nodes contacted. */
@@ -2927,8 +3238,7 @@ int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
 	set_bit(old_master, iter.node_map);
 	mlog(0, "doing assert master of %.*s back to %u\n",
 	     res->lockname.len, res->lockname.name, old_master);
-	ret = dlm_do_assert_master(dlm, res->lockname.name,
-				   res->lockname.len, iter.node_map,
+	ret = dlm_do_assert_master(dlm, res, iter.node_map,
 				   DLM_ASSERT_MASTER_FINISH_MIGRATION);
 	if (ret < 0) {
 		mlog(0, "assert master to original master failed "
diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index 367a11e9e2ed..d011a2a22742 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1129,6 +1129,11 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
 	if (total_locks == mres_total_locks)
 		mres->flags |= DLM_MRES_ALL_DONE;
 
+	mlog(0, "%s:%.*s: sending mig lockres (%s) to %u\n",
+	     dlm->name, res->lockname.len, res->lockname.name,
+	     orig_flags & DLM_MRES_MIGRATION ? "migrate" : "recovery",
+	     send_to);
+
 	/* send it */
 	ret = o2net_send_message(DLM_MIG_LOCKRES_MSG, dlm->key, mres,
 				 sz, send_to, &status);
@@ -1213,6 +1218,34 @@ static int dlm_add_lock_to_array(struct dlm_lock *lock,
 	return 0;
 }
 
+static void dlm_add_dummy_lock(struct dlm_ctxt *dlm,
+			       struct dlm_migratable_lockres *mres)
+{
+	struct dlm_lock dummy;
+	memset(&dummy, 0, sizeof(dummy));
+	dummy.ml.cookie = 0;
+	dummy.ml.type = LKM_IVMODE;
+	dummy.ml.convert_type = LKM_IVMODE;
+	dummy.ml.highest_blocked = LKM_IVMODE;
+	dummy.lksb = NULL;
+	dummy.ml.node = dlm->node_num;
+	dlm_add_lock_to_array(&dummy, mres, DLM_BLOCKED_LIST);
+}
+
+static inline int dlm_is_dummy_lock(struct dlm_ctxt *dlm,
+				    struct dlm_migratable_lock *ml,
+				    u8 *nodenum)
+{
+	if (unlikely(ml->cookie == 0 &&
+	    ml->type == LKM_IVMODE &&
+	    ml->convert_type == LKM_IVMODE &&
+	    ml->highest_blocked == LKM_IVMODE &&
+	    ml->list == DLM_BLOCKED_LIST)) {
+		*nodenum = ml->node;
+		return 1;
+	}
+	return 0;
+}
 
 int dlm_send_one_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
 			 struct dlm_migratable_lockres *mres,
@@ -1260,6 +1293,14 @@ int dlm_send_one_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
 				goto error;
 		}
 	}
+	if (total_locks == 0) {
+		/* send a dummy lock to indicate a mastery reference only */
+		mlog(0, "%s:%.*s: sending dummy lock to %u, %s\n",
+		     dlm->name, res->lockname.len, res->lockname.name,
+		     send_to, flags & DLM_MRES_RECOVERY ? "recovery" :
+		     "migration");
+		dlm_add_dummy_lock(dlm, mres);
+	}
 	/* flush any remaining locks */
 	ret = dlm_send_mig_lockres_msg(dlm, mres, send_to, res, total_locks);
 	if (ret < 0)
@@ -1386,13 +1427,16 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data)
 		/* add an extra ref for just-allocated lockres 
 		 * otherwise the lockres will be purged immediately */
 		dlm_lockres_get(res);
-
 	}
 
 	/* at this point we have allocated everything we need,
 	 * and we have a hashed lockres with an extra ref and
 	 * the proper res->state flags. */
 	ret = 0;
+	spin_lock(&res->spinlock);
+	/* drop this either when master requery finds a different master
+	 * or when a lock is added by the recovery worker */
+	dlm_lockres_grab_inflight_ref(dlm, res);
 	if (mres->master == DLM_LOCK_RES_OWNER_UNKNOWN) {
 		/* migration cannot have an unknown master */
 		BUG_ON(!(mres->flags & DLM_MRES_RECOVERY));
@@ -1400,10 +1444,11 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data)
 			  "unknown owner.. will need to requery: "
 			  "%.*s\n", mres->lockname_len, mres->lockname);
 	} else {
-		spin_lock(&res->spinlock);
+		/* take a reference now to pin the lockres, drop it
+		 * when locks are added in the worker */
 		dlm_change_lockres_owner(dlm, res, dlm->node_num);
-		spin_unlock(&res->spinlock);
 	}
+	spin_unlock(&res->spinlock);
 
 	/* queue up work for dlm_mig_lockres_worker */
 	dlm_grab(dlm);  /* get an extra ref for the work item */
@@ -1459,6 +1504,9 @@ again:
 				   "this node will take it.\n",
 				   res->lockname.len, res->lockname.name);
 		} else {
+			spin_lock(&res->spinlock);
+			dlm_lockres_drop_inflight_ref(dlm, res);
+			spin_unlock(&res->spinlock);
 			mlog(0, "master needs to respond to sender "
 				  "that node %u still owns %.*s\n",
 				  real_master, res->lockname.len,
@@ -1666,10 +1714,25 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 	int i, bad;
 	struct list_head *iter;
 	struct dlm_lock *lock = NULL;
+	u8 from = O2NM_MAX_NODES;
+	unsigned int added = 0;
 
 	mlog(0, "running %d locks for this lockres\n", mres->num_locks);
 	for (i=0; i<mres->num_locks; i++) {
 		ml = &(mres->ml[i]);
+
+		if (dlm_is_dummy_lock(dlm, ml, &from)) {
+			/* placeholder, just need to set the refmap bit */
+			BUG_ON(mres->num_locks != 1);
+			mlog(0, "%s:%.*s: dummy lock for %u\n",
+			     dlm->name, mres->lockname_len, mres->lockname,
+			     from);
+			spin_lock(&res->spinlock);
+			dlm_lockres_set_refmap_bit(from, res);
+			spin_unlock(&res->spinlock);
+			added++;
+			break;
+		}
 		BUG_ON(ml->highest_blocked != LKM_IVMODE);
 		newlock = NULL;
 		lksb = NULL;
@@ -1711,6 +1774,7 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 			/* do not alter lock refcount.  switching lists. */
 			list_move_tail(&lock->list, queue);
 			spin_unlock(&res->spinlock);
+			added++;
 
 			mlog(0, "just reordered a local lock!\n");
 			continue;
@@ -1817,12 +1881,24 @@ skip_lvb:
 		if (!bad) {
 			dlm_lock_get(newlock);
 			list_add_tail(&newlock->list, queue);
+			mlog(0, "%s:%.*s: added lock for node %u, "
+			     "setting refmap bit\n", dlm->name,
+			     res->lockname.len, res->lockname.name, ml->node);
+			dlm_lockres_set_refmap_bit(ml->node, res);
+			added++;
 		}
 		spin_unlock(&res->spinlock);
 	}
 	mlog(0, "done running all the locks\n");
 
 leave:
+	/* balance the ref taken when the work was queued */
+	if (added > 0) {
+		spin_lock(&res->spinlock);
+		dlm_lockres_drop_inflight_ref(dlm, res);
+		spin_unlock(&res->spinlock);
+	}
+
 	if (ret < 0) {
 		mlog_errno(ret);
 		if (newlock)
@@ -1935,9 +2011,11 @@ static void dlm_finish_local_lockres_recovery(struct dlm_ctxt *dlm,
 		if (res->owner == dead_node) {
 			list_del_init(&res->recovering);
 			spin_lock(&res->spinlock);
+			/* new_master has our reference from
+			 * the lock state sent during recovery */
 			dlm_change_lockres_owner(dlm, res, new_master);
 			res->state &= ~DLM_LOCK_RES_RECOVERING;
-			if (!__dlm_lockres_unused(res))
+			if (__dlm_lockres_has_locks(res))
 				__dlm_dirty_lockres(dlm, res);
 			spin_unlock(&res->spinlock);
 			wake_up(&res->wq);
@@ -1977,9 +2055,11 @@ static void dlm_finish_local_lockres_recovery(struct dlm_ctxt *dlm,
 					dlm_lockres_put(res);
 				}
 				spin_lock(&res->spinlock);
+				/* new_master has our reference from
+				 * the lock state sent during recovery */
 				dlm_change_lockres_owner(dlm, res, new_master);
 				res->state &= ~DLM_LOCK_RES_RECOVERING;
-				if (!__dlm_lockres_unused(res))
+				if (__dlm_lockres_has_locks(res))
 					__dlm_dirty_lockres(dlm, res);
 				spin_unlock(&res->spinlock);
 				wake_up(&res->wq);
@@ -2048,6 +2128,7 @@ static void dlm_free_dead_locks(struct dlm_ctxt *dlm,
 {
 	struct list_head *iter, *tmpiter;
 	struct dlm_lock *lock;
+	unsigned int freed = 0;
 
 	/* this node is the lockres master:
 	 * 1) remove any stale locks for the dead node
@@ -2062,6 +2143,7 @@ static void dlm_free_dead_locks(struct dlm_ctxt *dlm,
 		if (lock->ml.node == dead_node) {
 			list_del_init(&lock->list);
 			dlm_lock_put(lock);
+			freed++;
 		}
 	}
 	list_for_each_safe(iter, tmpiter, &res->converting) {
@@ -2069,6 +2151,7 @@ static void dlm_free_dead_locks(struct dlm_ctxt *dlm,
 		if (lock->ml.node == dead_node) {
 			list_del_init(&lock->list);
 			dlm_lock_put(lock);
+			freed++;
 		}
 	}
 	list_for_each_safe(iter, tmpiter, &res->blocked) {
@@ -2076,9 +2159,23 @@ static void dlm_free_dead_locks(struct dlm_ctxt *dlm,
 		if (lock->ml.node == dead_node) {
 			list_del_init(&lock->list);
 			dlm_lock_put(lock);
+			freed++;
 		}
 	}
 
+	if (freed) {
+		mlog(0, "%s:%.*s: freed %u locks for dead node %u, "
+		     "dropping ref from lockres\n", dlm->name,
+		     res->lockname.len, res->lockname.name, freed, dead_node);
+		BUG_ON(!test_bit(dead_node, res->refmap));
+		dlm_lockres_clear_refmap_bit(dead_node, res);
+	} else if (test_bit(dead_node, res->refmap)) {
+		mlog(0, "%s:%.*s: dead node %u had a ref, but had "
+		     "no locks and had not purged before dying\n", dlm->name,
+		     res->lockname.len, res->lockname.name, dead_node);
+		dlm_lockres_clear_refmap_bit(dead_node, res);
+	}
+
 	/* do not kick thread yet */
 	__dlm_dirty_lockres(dlm, res);
 }
@@ -2141,9 +2238,21 @@ static void dlm_do_local_recovery_cleanup(struct dlm_ctxt *dlm, u8 dead_node)
 			spin_lock(&res->spinlock);
 			/* zero the lvb if necessary */
 			dlm_revalidate_lvb(dlm, res, dead_node);
-			if (res->owner == dead_node)
+			if (res->owner == dead_node) {
+				if (res->state & DLM_LOCK_RES_DROPPING_REF)
+					mlog(0, "%s:%.*s: owned by "
+					     "dead node %u, this node was "
+					     "dropping its ref when it died. "
+					     "continue, dropping the flag.\n",
+					     dlm->name, res->lockname.len,
+					     res->lockname.name, dead_node);
+
+				/* the wake_up for this will happen when the
+				 * RECOVERING flag is dropped later */
+				res->state &= ~DLM_LOCK_RES_DROPPING_REF;
+
 				dlm_move_lockres_to_recovery_list(dlm, res);
-			else if (res->owner == dlm->node_num) {
+			} else if (res->owner == dlm->node_num) {
 				dlm_free_dead_locks(dlm, res, dead_node);
 				__dlm_lockres_calc_usage(dlm, res);
 			}
diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
index 0c822f3ffb05..620eb824ce1d 100644
--- a/fs/ocfs2/dlm/dlmthread.c
+++ b/fs/ocfs2/dlm/dlmthread.c
@@ -54,9 +54,6 @@
 #include "cluster/masklog.h"
 
 static int dlm_thread(void *data);
-static void dlm_purge_lockres_now(struct dlm_ctxt *dlm,
-				  struct dlm_lock_resource *lockres);
-
 static void dlm_flush_asts(struct dlm_ctxt *dlm);
 
 #define dlm_lock_is_remote(dlm, lock)     ((lock)->ml.node != (dlm)->node_num)
@@ -82,14 +79,33 @@ repeat:
 	current->state = TASK_RUNNING;
 }
 
-
-int __dlm_lockres_unused(struct dlm_lock_resource *res)
+int __dlm_lockres_has_locks(struct dlm_lock_resource *res)
 {
 	if (list_empty(&res->granted) &&
 	    list_empty(&res->converting) &&
-	    list_empty(&res->blocked) &&
-	    list_empty(&res->dirty))
-		return 1;
+	    list_empty(&res->blocked))
+		return 0;
+	return 1;
+}
+
+/* "unused": the lockres has no locks, is not on the dirty list,
+ * has no inflight locks (in the gap between mastery and acquiring
+ * the first lock), and has no bits in its refmap.
+ * truly ready to be freed. */
+int __dlm_lockres_unused(struct dlm_lock_resource *res)
+{
+	if (!__dlm_lockres_has_locks(res) &&
+	    list_empty(&res->dirty)) {
+		/* try not to scan the bitmap unless the first two
+		 * conditions are already true */
+		int bit = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
+		if (bit >= O2NM_MAX_NODES) {
+			/* since the bit for dlm->node_num is not
+			 * set, inflight_locks better be zero */
+			BUG_ON(res->inflight_locks != 0);
+			return 1;
+		}
+	}
 	return 0;
 }
 
@@ -106,46 +122,21 @@ void __dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
 	assert_spin_locked(&res->spinlock);
 
 	if (__dlm_lockres_unused(res)){
-		/* For now, just keep any resource we master */
-		if (res->owner == dlm->node_num)
-		{
-			if (!list_empty(&res->purge)) {
-				mlog(0, "we master %s:%.*s, but it is on "
-				     "the purge list.  Removing\n",
-				     dlm->name, res->lockname.len,
-				     res->lockname.name);
-				list_del_init(&res->purge);
-				dlm->purge_count--;
-			}
-			return;
-		}
-
 		if (list_empty(&res->purge)) {
-			mlog(0, "putting lockres %.*s from purge list\n",
-			     res->lockname.len, res->lockname.name);
+			mlog(0, "putting lockres %.*s:%p onto purge list\n",
+			     res->lockname.len, res->lockname.name, res);
 
 			res->last_used = jiffies;
+			dlm_lockres_get(res);
 			list_add_tail(&res->purge, &dlm->purge_list);
 			dlm->purge_count++;
-
-			/* if this node is not the owner, there is
-			 * no way to keep track of who the owner could be.
-			 * unhash it to avoid serious problems. */
-			if (res->owner != dlm->node_num) {
-				mlog(0, "%s:%.*s: doing immediate "
-				     "purge of lockres owned by %u\n",
-				     dlm->name, res->lockname.len,
-				     res->lockname.name, res->owner);
-
-				dlm_purge_lockres_now(dlm, res);
-			}
 		}
 	} else if (!list_empty(&res->purge)) {
-		mlog(0, "removing lockres %.*s from purge list, "
-		     "owner=%u\n", res->lockname.len, res->lockname.name,
-		     res->owner);
+		mlog(0, "removing lockres %.*s:%p from purge list, owner=%u\n",
+		     res->lockname.len, res->lockname.name, res, res->owner);
 
 		list_del_init(&res->purge);
+		dlm_lockres_put(res);
 		dlm->purge_count--;
 	}
 }
@@ -163,68 +154,60 @@ void dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
 	spin_unlock(&dlm->spinlock);
 }
 
-/* TODO: Eventual API: Called with the dlm spinlock held, may drop it
- * to do migration, but will re-acquire before exit. */
-void dlm_purge_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *lockres)
+int dlm_purge_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
 {
 	int master;
-	int ret;
-
-	spin_lock(&lockres->spinlock);
-	master = lockres->owner == dlm->node_num;
-	spin_unlock(&lockres->spinlock);
-
-	mlog(0, "purging lockres %.*s, master = %d\n", lockres->lockname.len,
-	     lockres->lockname.name, master);
+	int ret = 0;
 
-	/* Non master is the easy case -- no migration required, just
-	 * quit. */
+	spin_lock(&res->spinlock);
+	if (!__dlm_lockres_unused(res)) {
+		spin_unlock(&res->spinlock);
+		mlog(0, "%s:%.*s: tried to purge but not unused\n",
+		     dlm->name, res->lockname.len, res->lockname.name);
+		return -ENOTEMPTY;
+	}
+	master = (res->owner == dlm->node_num);
 	if (!master)
-		goto finish;
-
-	/* Wheee! Migrate lockres here! */
-	spin_unlock(&dlm->spinlock);
-again:
+		res->state |= DLM_LOCK_RES_DROPPING_REF;
+	spin_unlock(&res->spinlock);
 
-	ret = dlm_migrate_lockres(dlm, lockres, O2NM_MAX_NODES);
-	if (ret == -ENOTEMPTY) {
-		mlog(ML_ERROR, "lockres %.*s still has local locks!\n",
-		     lockres->lockname.len, lockres->lockname.name);
+	mlog(0, "purging lockres %.*s, master = %d\n", res->lockname.len,
+	     res->lockname.name, master);
 
-		BUG();
-	} else if (ret < 0) {
-		mlog(ML_NOTICE, "lockres %.*s: migrate failed, retrying\n",
-		     lockres->lockname.len, lockres->lockname.name);
-		msleep(100);
-		goto again;
+	if (!master) {
+		/* drop spinlock to do messaging, retake below */
+		spin_unlock(&dlm->spinlock);
+		/* clear our bit from the master's refmap, ignore errors */
+		ret = dlm_drop_lockres_ref(dlm, res);
+		if (ret < 0) {
+			mlog_errno(ret);
+			if (!dlm_is_host_down(ret))
+				BUG();
+		}
+		mlog(0, "%s:%.*s: dlm_deref_lockres returned %d\n",
+		     dlm->name, res->lockname.len, res->lockname.name, ret);
+		spin_lock(&dlm->spinlock);
 	}
 
-	spin_lock(&dlm->spinlock);
-
-finish:
-	if (!list_empty(&lockres->purge)) {
-		list_del_init(&lockres->purge);
+	if (!list_empty(&res->purge)) {
+		mlog(0, "removing lockres %.*s:%p from purgelist, "
+		     "master = %d\n", res->lockname.len, res->lockname.name,
+		     res, master);
+		list_del_init(&res->purge);
+		dlm_lockres_put(res);
 		dlm->purge_count--;
 	}
-	__dlm_unhash_lockres(lockres);
-}
-
-/* make an unused lockres go away immediately.
- * as soon as the dlm spinlock is dropped, this lockres
- * will not be found. kfree still happens on last put. */
-static void dlm_purge_lockres_now(struct dlm_ctxt *dlm,
-				  struct dlm_lock_resource *lockres)
-{
-	assert_spin_locked(&dlm->spinlock);
-	assert_spin_locked(&lockres->spinlock);
-
-	BUG_ON(!__dlm_lockres_unused(lockres));
+	__dlm_unhash_lockres(res);
 
-	if (!list_empty(&lockres->purge)) {
-		list_del_init(&lockres->purge);
-		dlm->purge_count--;
+	/* lockres is not in the hash now.  drop the flag and wake up
+	 * any processes waiting in dlm_get_lock_resource. */
+	if (!master) {
+		spin_lock(&res->spinlock);
+		res->state &= ~DLM_LOCK_RES_DROPPING_REF;
+		spin_unlock(&res->spinlock);
+		wake_up(&res->wq);
 	}
-	__dlm_unhash_lockres(lockres);
+	return 0;
 }
 
 static void dlm_run_purge_list(struct dlm_ctxt *dlm,
@@ -268,13 +251,17 @@ static void dlm_run_purge_list(struct dlm_ctxt *dlm,
 			break;
 		}
 
+		mlog(0, "removing lockres %.*s:%p from purgelist\n",
+		     lockres->lockname.len, lockres->lockname.name, lockres);
 		list_del_init(&lockres->purge);
+		dlm_lockres_put(lockres);
 		dlm->purge_count--;
 
 		/* This may drop and reacquire the dlm spinlock if it
 		 * has to do migration. */
 		mlog(0, "calling dlm_purge_lockres!\n");
-		dlm_purge_lockres(dlm, lockres);
+		if (dlm_purge_lockres(dlm, lockres))
+			BUG();
 		mlog(0, "DONE calling dlm_purge_lockres!\n");
 
 		/* Avoid adding any scheduling latencies */