12 files changed, 378 insertions, 172 deletions

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index 5b79cdceefa0..52233fa6195f 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -18,8 +18,10 @@
 static unsigned __read_mostly afs_cell_gc_delay = 10;
 static unsigned __read_mostly afs_cell_min_ttl = 10 * 60;
 static unsigned __read_mostly afs_cell_max_ttl = 24 * 60 * 60;
+static atomic_t cell_debug_id;
 
-static void afs_manage_cell(struct work_struct *);
+static void afs_queue_cell_manager(struct afs_net *);
+static void afs_manage_cell_work(struct work_struct *);
 
 static void afs_dec_cells_outstanding(struct afs_net *net)
 {
@@ -37,19 +39,22 @@ static void afs_set_cell_timer(struct afs_net *net, time64_t delay)
 		atomic_inc(&net->cells_outstanding);
 		if (timer_reduce(&net->cells_timer, jiffies + delay * HZ))
 			afs_dec_cells_outstanding(net);
+	} else {
+		afs_queue_cell_manager(net);
 	}
 }
 
 /*
- * Look up and get an activation reference on a cell record under RCU
- * conditions.  The caller must hold the RCU read lock.
+ * Look up and get an activation reference on a cell record.  The caller must
+ * hold net->cells_lock at least read-locked.
  */
-struct afs_cell *afs_lookup_cell_rcu(struct afs_net *net,
-				     const char *name, unsigned int namesz)
+static struct afs_cell *afs_find_cell_locked(struct afs_net *net,
+					     const char *name, unsigned int namesz,
+					     enum afs_cell_trace reason)
 {
 	struct afs_cell *cell = NULL;
 	struct rb_node *p;
-	int n, seq = 0, ret = 0;
+	int n;
 
 	_enter("%*.*s", namesz, namesz, name);
 
@@ -58,61 +63,48 @@ struct afs_cell *afs_lookup_cell_rcu(struct afs_net *net,
 	if (namesz > AFS_MAXCELLNAME)
 		return ERR_PTR(-ENAMETOOLONG);
 
-	do {
-		/* Unfortunately, rbtree walking doesn't give reliable results
-		 * under just the RCU read lock, so we have to check for
-		 * changes.
-		 */
-		if (cell)
-			afs_put_cell(net, cell);
-		cell = NULL;
-		ret = -ENOENT;
-
-		read_seqbegin_or_lock(&net->cells_lock, &seq);
-
-		if (!name) {
-			cell = rcu_dereference_raw(net->ws_cell);
-			if (cell) {
-				afs_get_cell(cell);
-				ret = 0;
-				break;
-			}
-			ret = -EDESTADDRREQ;
-			continue;
-		}
+	if (!name) {
+		cell = net->ws_cell;
+		if (!cell)
+			return ERR_PTR(-EDESTADDRREQ);
+		goto found;
+	}
 
-		p = rcu_dereference_raw(net->cells.rb_node);
-		while (p) {
-			cell = rb_entry(p, struct afs_cell, net_node);
-
-			n = strncasecmp(cell->name, name,
-					min_t(size_t, cell->name_len, namesz));
-			if (n == 0)
-				n = cell->name_len - namesz;
-			if (n < 0) {
-				p = rcu_dereference_raw(p->rb_left);
-			} else if (n > 0) {
-				p = rcu_dereference_raw(p->rb_right);
-			} else {
-				if (atomic_inc_not_zero(&cell->usage)) {
-					ret = 0;
-					break;
-				}
-				/* We want to repeat the search, this time with
-				 * the lock properly locked.
-				 */
-			}
-			cell = NULL;
-		}
+	p = net->cells.rb_node;
+	while (p) {
+		cell = rb_entry(p, struct afs_cell, net_node);
 
-	} while (need_seqretry(&net->cells_lock, seq));
+		n = strncasecmp(cell->name, name,
+				min_t(size_t, cell->name_len, namesz));
+		if (n == 0)
+			n = cell->name_len - namesz;
+		if (n < 0)
+			p = p->rb_left;
+		else if (n > 0)
+			p = p->rb_right;
+		else
+			goto found;
+	}
 
-	done_seqretry(&net->cells_lock, seq);
+	return ERR_PTR(-ENOENT);
 
-	if (ret != 0 && cell)
-		afs_put_cell(net, cell);
+found:
+	return afs_use_cell(cell, reason);
+}
 
-	return ret == 0 ? cell : ERR_PTR(ret);
+/*
+ * Look up and get an activation reference on a cell record.
+ */
+struct afs_cell *afs_find_cell(struct afs_net *net,
+			       const char *name, unsigned int namesz,
+			       enum afs_cell_trace reason)
+{
+	struct afs_cell *cell;
+
+	down_read(&net->cells_lock);
+	cell = afs_find_cell_locked(net, name, namesz, reason);
+	up_read(&net->cells_lock);
+	return cell;
 }
 
 /*
@@ -166,8 +158,9 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
 		cell->name[i] = tolower(name[i]);
 	cell->name[i] = 0;
 
-	atomic_set(&cell->usage, 2);
-	INIT_WORK(&cell->manager, afs_manage_cell);
+	atomic_set(&cell->ref, 1);
+	atomic_set(&cell->active, 0);
+	INIT_WORK(&cell->manager, afs_manage_cell_work);
 	cell->volumes = RB_ROOT;
 	INIT_HLIST_HEAD(&cell->proc_volumes);
 	seqlock_init(&cell->volume_lock);
@@ -206,6 +199,9 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
 	cell->dns_source = vllist->source;
 	cell->dns_status = vllist->status;
 	smp_store_release(&cell->dns_lookup_count, 1); /* vs source/status */
+	atomic_inc(&net->cells_outstanding);
+	cell->debug_id = atomic_inc_return(&cell_debug_id);
+	trace_afs_cell(cell->debug_id, 1, 0, afs_cell_trace_alloc);
 
 	_leave(" = %p", cell);
 	return cell;
@@ -245,9 +241,7 @@ struct afs_cell *afs_lookup_cell(struct afs_net *net,
 	_enter("%s,%s", name, vllist);
 
 	if (!excl) {
-		rcu_read_lock();
-		cell = afs_lookup_cell_rcu(net, name, namesz);
-		rcu_read_unlock();
+		cell = afs_find_cell(net, name, namesz, afs_cell_trace_use_lookup);
 		if (!IS_ERR(cell))
 			goto wait_for_cell;
 	}
@@ -268,7 +262,7 @@ struct afs_cell *afs_lookup_cell(struct afs_net *net,
 	/* Find the insertion point and check to see if someone else added a
 	 * cell whilst we were allocating.
 	 */
-	write_seqlock(&net->cells_lock);
+	down_write(&net->cells_lock);
 
 	pp = &net->cells.rb_node;
 	parent = NULL;
@@ -290,23 +284,26 @@ struct afs_cell *afs_lookup_cell(struct afs_net *net,
 
 	cell = candidate;
 	candidate = NULL;
+	atomic_set(&cell->active, 2);
+	trace_afs_cell(cell->debug_id, atomic_read(&cell->ref), 2, afs_cell_trace_insert);
 	rb_link_node_rcu(&cell->net_node, parent, pp);
 	rb_insert_color(&cell->net_node, &net->cells);
-	atomic_inc(&net->cells_outstanding);
-	write_sequnlock(&net->cells_lock);
+	up_write(&net->cells_lock);
 
-	queue_work(afs_wq, &cell->manager);
+	afs_queue_cell(cell, afs_cell_trace_get_queue_new);
 
 wait_for_cell:
+	trace_afs_cell(cell->debug_id, atomic_read(&cell->ref), atomic_read(&cell->active),
+		       afs_cell_trace_wait);
 	_debug("wait_for_cell");
 	wait_var_event(&cell->state,
 		       ({
 			       state = smp_load_acquire(&cell->state); /* vs error */
-			       state == AFS_CELL_ACTIVE || state == AFS_CELL_FAILED;
+			       state == AFS_CELL_ACTIVE || state == AFS_CELL_REMOVED;
 		       }));
 
 	/* Check the state obtained from the wait check. */
-	if (state == AFS_CELL_FAILED) {
+	if (state == AFS_CELL_REMOVED) {
 		ret = cell->error;
 		goto error;
 	}
@@ -320,16 +317,17 @@ cell_already_exists:
 	if (excl) {
 		ret = -EEXIST;
 	} else {
-		afs_get_cell(cursor);
+		afs_use_cell(cursor, afs_cell_trace_use_lookup);
 		ret = 0;
 	}
-	write_sequnlock(&net->cells_lock);
-	kfree(candidate);
+	up_write(&net->cells_lock);
+	if (candidate)
+		afs_put_cell(candidate, afs_cell_trace_put_candidate);
 	if (ret == 0)
 		goto wait_for_cell;
 	goto error_noput;
 error:
-	afs_put_cell(net, cell);
+	afs_unuse_cell(net, cell, afs_cell_trace_unuse_lookup);
 error_noput:
 	_leave(" = %d [error]", ret);
 	return ERR_PTR(ret);
@@ -374,15 +372,16 @@ int afs_cell_init(struct afs_net *net, const char *rootcell)
 	}
 
 	if (!test_and_set_bit(AFS_CELL_FL_NO_GC, &new_root->flags))
-		afs_get_cell(new_root);
+		afs_use_cell(new_root, afs_cell_trace_use_pin);
 
 	/* install the new cell */
-	write_seqlock(&net->cells_lock);
-	old_root = rcu_access_pointer(net->ws_cell);
-	rcu_assign_pointer(net->ws_cell, new_root);
-	write_sequnlock(&net->cells_lock);
+	down_write(&net->cells_lock);
+	afs_see_cell(new_root, afs_cell_trace_see_ws);
+	old_root = net->ws_cell;
+	net->ws_cell = new_root;
+	up_write(&net->cells_lock);
 
-	afs_put_cell(net, old_root);
+	afs_unuse_cell(net, old_root, afs_cell_trace_unuse_ws);
 	_leave(" = 0");
 	return 0;
 }
@@ -488,18 +487,22 @@ out_wake:
 static void afs_cell_destroy(struct rcu_head *rcu)
 {
 	struct afs_cell *cell = container_of(rcu, struct afs_cell, rcu);
+	struct afs_net *net = cell->net;
+	int u;
 
 	_enter("%p{%s}", cell, cell->name);
 
-	ASSERTCMP(atomic_read(&cell->usage), ==, 0);
+	u = atomic_read(&cell->ref);
+	ASSERTCMP(u, ==, 0);
+	trace_afs_cell(cell->debug_id, u, atomic_read(&cell->active), afs_cell_trace_free);
 
-	afs_put_volume(cell->net, cell->root_volume, afs_volume_trace_put_cell_root);
-	afs_put_vlserverlist(cell->net, rcu_access_pointer(cell->vl_servers));
-	afs_put_cell(cell->net, cell->alias_of);
+	afs_put_vlserverlist(net, rcu_access_pointer(cell->vl_servers));
+	afs_unuse_cell(net, cell->alias_of, afs_cell_trace_unuse_alias);
 	key_put(cell->anonymous_key);
 	kfree(cell->name);
 	kfree(cell);
 
+	afs_dec_cells_outstanding(net);
 	_leave(" [destroyed]");
 }
 
@@ -532,18 +535,63 @@ void afs_cells_timer(struct timer_list *timer)
 /*
  * Get a reference on a cell record.
  */
-struct afs_cell *afs_get_cell(struct afs_cell *cell)
+struct afs_cell *afs_get_cell(struct afs_cell *cell, enum afs_cell_trace reason)
 {
-	atomic_inc(&cell->usage);
+	int u;
+
+	if (atomic_read(&cell->ref) <= 0)
+		BUG();
+
+	u = atomic_inc_return(&cell->ref);
+	trace_afs_cell(cell->debug_id, u, atomic_read(&cell->active), reason);
 	return cell;
 }
 
 /*
  * Drop a reference on a cell record.
  */
-void afs_put_cell(struct afs_net *net, struct afs_cell *cell)
+void afs_put_cell(struct afs_cell *cell, enum afs_cell_trace reason)
 {
+	if (cell) {
+		unsigned int debug_id = cell->debug_id;
+		unsigned int u, a;
+
+		a = atomic_read(&cell->active);
+		u = atomic_dec_return(&cell->ref);
+		trace_afs_cell(debug_id, u, a, reason);
+		if (u == 0) {
+			a = atomic_read(&cell->active);
+			WARN(a != 0, "Cell active count %u > 0\n", a);
+			call_rcu(&cell->rcu, afs_cell_destroy);
+		}
+	}
+}
+
+/*
+ * Note a cell becoming more active.
+ */
+struct afs_cell *afs_use_cell(struct afs_cell *cell, enum afs_cell_trace reason)
+{
+	int u, a;
+
+	if (atomic_read(&cell->ref) <= 0)
+		BUG();
+
+	u = atomic_read(&cell->ref);
+	a = atomic_inc_return(&cell->active);
+	trace_afs_cell(cell->debug_id, u, a, reason);
+	return cell;
+}
+
+/*
+ * Record a cell becoming less active.  When the active counter reaches 1, it
+ * is scheduled for destruction, but may get reactivated.
+ */
+void afs_unuse_cell(struct afs_net *net, struct afs_cell *cell, enum afs_cell_trace reason)
+{
+	unsigned int debug_id = cell->debug_id;
 	time64_t now, expire_delay;
+	int u, a;
 
 	if (!cell)
 		return;
@@ -556,11 +604,35 @@ void afs_put_cell(struct afs_net *net, struct afs_cell *cell)
 	if (cell->vl_servers->nr_servers)
 		expire_delay = afs_cell_gc_delay;
 
-	if (atomic_dec_return(&cell->usage) > 1)
-		return;
+	u = atomic_read(&cell->ref);
+	a = atomic_dec_return(&cell->active);
+	trace_afs_cell(debug_id, u, a, reason);
+	WARN_ON(a == 0);
+	if (a == 1)
+		/* 'cell' may now be garbage collected. */
+		afs_set_cell_timer(net, expire_delay);
+}
+
+/*
+ * Note that a cell has been seen.
+ */
+void afs_see_cell(struct afs_cell *cell, enum afs_cell_trace reason)
+{
+	int u, a;
+
+	u = atomic_read(&cell->ref);
+	a = atomic_read(&cell->active);
+	trace_afs_cell(cell->debug_id, u, a, reason);
+}
 
-	/* 'cell' may now be garbage collected. */
-	afs_set_cell_timer(net, expire_delay);
+/*
+ * Queue a cell for management, giving the workqueue a ref to hold.
+ */
+void afs_queue_cell(struct afs_cell *cell, enum afs_cell_trace reason)
+{
+	afs_get_cell(cell, reason);
+	if (!queue_work(afs_wq, &cell->manager))
+		afs_put_cell(cell, afs_cell_trace_put_queue_fail);
 }
 
 /*
@@ -660,12 +732,10 @@ static void afs_deactivate_cell(struct afs_net *net, struct afs_cell *cell)
  * Manage a cell record, initialising and destroying it, maintaining its DNS
  * records.
  */
-static void afs_manage_cell(struct work_struct *work)
+static void afs_manage_cell(struct afs_cell *cell)
 {
-	struct afs_cell *cell = container_of(work, struct afs_cell, manager);
 	struct afs_net *net = cell->net;
-	bool deleted;
-	int ret, usage;
+	int ret, active;
 
 	_enter("%s", cell->name);
 
@@ -674,14 +744,19 @@ again:
 	switch (cell->state) {
 	case AFS_CELL_INACTIVE:
 	case AFS_CELL_FAILED:
-		write_seqlock(&net->cells_lock);
-		usage = 1;
-		deleted = atomic_try_cmpxchg_relaxed(&cell->usage, &usage, 0);
-		if (deleted)
+		down_write(&net->cells_lock);
+		active = 1;
+		if (atomic_try_cmpxchg_relaxed(&cell->active, &active, 0)) {
 			rb_erase(&cell->net_node, &net->cells);
-		write_sequnlock(&net->cells_lock);
-		if (deleted)
+			trace_afs_cell(cell->debug_id, atomic_read(&cell->ref), 0,
+				       afs_cell_trace_unuse_delete);
+			smp_store_release(&cell->state, AFS_CELL_REMOVED);
+		}
+		up_write(&net->cells_lock);
+		if (cell->state == AFS_CELL_REMOVED) {
+			wake_up_var(&cell->state);
 			goto final_destruction;
+		}
 		if (cell->state == AFS_CELL_FAILED)
 			goto done;
 		smp_store_release(&cell->state, AFS_CELL_UNSET);
@@ -703,7 +778,7 @@ again:
 		goto again;
 
 	case AFS_CELL_ACTIVE:
-		if (atomic_read(&cell->usage) > 1) {
+		if (atomic_read(&cell->active) > 1) {
 			if (test_and_clear_bit(AFS_CELL_FL_DO_LOOKUP, &cell->flags)) {
 				ret = afs_update_cell(cell);
 				if (ret < 0)
@@ -716,13 +791,16 @@ again:
 		goto again;
 
 	case AFS_CELL_DEACTIVATING:
-		if (atomic_read(&cell->usage) > 1)
+		if (atomic_read(&cell->active) > 1)
 			goto reverse_deactivation;
 		afs_deactivate_cell(net, cell);
 		smp_store_release(&cell->state, AFS_CELL_INACTIVE);
 		wake_up_var(&cell->state);
 		goto again;
 
+	case AFS_CELL_REMOVED:
+		goto done;
+
 	default:
 		break;
 	}
@@ -748,9 +826,18 @@ done:
 	return;
 
 final_destruction:
-	call_rcu(&cell->rcu, afs_cell_destroy);
-	afs_dec_cells_outstanding(net);
-	_leave(" [destruct %d]", atomic_read(&net->cells_outstanding));
+	/* The root volume is pinning the cell */
+	afs_put_volume(cell->net, cell->root_volume, afs_volume_trace_put_cell_root);
+	cell->root_volume = NULL;
+	afs_put_cell(cell, afs_cell_trace_put_destroy);
+}
+
+static void afs_manage_cell_work(struct work_struct *work)
+{
+	struct afs_cell *cell = container_of(work, struct afs_cell, manager);
+
+	afs_manage_cell(cell);
+	afs_put_cell(cell, afs_cell_trace_put_queue_work);
 }
 
 /*
@@ -779,26 +866,29 @@ void afs_manage_cells(struct work_struct *work)
 	 * lack of use and cells whose DNS results have expired and dispatch
 	 * their managers.
 	 */
-	read_seqlock_excl(&net->cells_lock);
+	down_read(&net->cells_lock);
 
 	for (cursor = rb_first(&net->cells); cursor; cursor = rb_next(cursor)) {
 		struct afs_cell *cell =
 			rb_entry(cursor, struct afs_cell, net_node);
-		unsigned usage;
+		unsigned active;
 		bool sched_cell = false;
 
-		usage = atomic_read(&cell->usage);
-		_debug("manage %s %u", cell->name, usage);
+		active = atomic_read(&cell->active);
+		trace_afs_cell(cell->debug_id, atomic_read(&cell->ref),
+			       active, afs_cell_trace_manage);
 
-		ASSERTCMP(usage, >=, 1);
+		ASSERTCMP(active, >=, 1);
 
 		if (purging) {
-			if (test_and_clear_bit(AFS_CELL_FL_NO_GC, &cell->flags))
-				usage = atomic_dec_return(&cell->usage);
-			ASSERTCMP(usage, ==, 1);
+			if (test_and_clear_bit(AFS_CELL_FL_NO_GC, &cell->flags)) {
+				active = atomic_dec_return(&cell->active);
+				trace_afs_cell(cell->debug_id, atomic_read(&cell->ref),
+					       active, afs_cell_trace_unuse_pin);
+			}
 		}
 
-		if (usage == 1) {
+		if (active == 1) {
 			struct afs_vlserver_list *vllist;
 			time64_t expire_at = cell->last_inactive;
 
@@ -821,10 +911,10 @@ void afs_manage_cells(struct work_struct *work)
 		}
 
 		if (sched_cell)
-			queue_work(afs_wq, &cell->manager);
+			afs_queue_cell(cell, afs_cell_trace_get_queue_manage);
 	}
 
-	read_sequnlock_excl(&net->cells_lock);
+	up_read(&net->cells_lock);
 
 	/* Update the timer on the way out.  We have to pass an increment on
 	 * cells_outstanding in the namespace that we are in to the timer or
@@ -854,11 +944,11 @@ void afs_cell_purge(struct afs_net *net)
 
 	_enter("");
 
-	write_seqlock(&net->cells_lock);
-	ws = rcu_access_pointer(net->ws_cell);
-	RCU_INIT_POINTER(net->ws_cell, NULL);
-	write_sequnlock(&net->cells_lock);
-	afs_put_cell(net, ws);
+	down_write(&net->cells_lock);
+	ws = net->ws_cell;
+	net->ws_cell = NULL;
+	up_write(&net->cells_lock);
+	afs_unuse_cell(net, ws, afs_cell_trace_unuse_ws);
 
 	_debug("del timer");
 	if (del_timer_sync(&net->cells_timer))
diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 7b784af604fd..db832cc931c8 100644
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -123,9 +123,9 @@ static int afs_probe_cell_name(struct dentry *dentry)
 		len--;
 	}
 
-	cell = afs_lookup_cell_rcu(net, name, len);
+	cell = afs_find_cell(net, name, len, afs_cell_trace_use_probe);
 	if (!IS_ERR(cell)) {
-		afs_put_cell(net, cell);
+		afs_unuse_cell(net, cell, afs_cell_trace_unuse_probe);
 		return 0;
 	}
 
@@ -179,7 +179,6 @@ static struct dentry *afs_lookup_atcell(struct dentry *dentry)
 	struct afs_cell *cell;
 	struct afs_net *net = afs_d2net(dentry);
 	struct dentry *ret;
-	unsigned int seq = 0;
 	char *name;
 	int len;
 
@@ -191,17 +190,13 @@ static struct dentry *afs_lookup_atcell(struct dentry *dentry)
 	if (!name)
 		goto out_p;
 
-	rcu_read_lock();
-	do {
-		read_seqbegin_or_lock(&net->cells_lock, &seq);
-		cell = rcu_dereference_raw(net->ws_cell);
-		if (cell) {
-			len = cell->name_len;
-			memcpy(name, cell->name, len + 1);
-		}
-	} while (need_seqretry(&net->cells_lock, seq));
-	done_seqretry(&net->cells_lock, seq);
-	rcu_read_unlock();
+	down_read(&net->cells_lock);
+	cell = net->ws_cell;
+	if (cell) {
+		len = cell->name_len;
+		memcpy(name, cell->name, len + 1);
+	}
+	up_read(&net->cells_lock);
 
 	ret = ERR_PTR(-ENOENT);
 	if (!cell)
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index e5f0446f27e5..81b0485fd22a 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -263,11 +263,11 @@ struct afs_net {
 
 	/* Cell database */
 	struct rb_root		cells;
-	struct afs_cell __rcu	*ws_cell;
+	struct afs_cell		*ws_cell;
 	struct work_struct	cells_manager;
 	struct timer_list	cells_timer;
 	atomic_t		cells_outstanding;
-	seqlock_t		cells_lock;
+	struct rw_semaphore	cells_lock;
 	struct mutex		cells_alias_lock;
 
 	struct mutex		proc_cells_lock;
@@ -326,6 +326,7 @@ enum afs_cell_state {
 	AFS_CELL_DEACTIVATING,
 	AFS_CELL_INACTIVE,
 	AFS_CELL_FAILED,
+	AFS_CELL_REMOVED,
 };
 
 /*
@@ -363,7 +364,8 @@ struct afs_cell {
 #endif
 	time64_t		dns_expiry;	/* Time AFSDB/SRV record expires */
 	time64_t		last_inactive;	/* Time of last drop of usage count */
-	atomic_t		usage;
+	atomic_t		ref;		/* Struct refcount */
+	atomic_t		active;		/* Active usage counter */
 	unsigned long		flags;
 #define AFS_CELL_FL_NO_GC	0		/* The cell was added manually, don't auto-gc */
 #define AFS_CELL_FL_DO_LOOKUP	1		/* DNS lookup requested */
@@ -373,6 +375,7 @@ struct afs_cell {
 	enum dns_record_source	dns_source:8;	/* Latest source of data from lookup */
 	enum dns_lookup_status	dns_status:8;	/* Latest status of data from lookup */
 	unsigned int		dns_lookup_count; /* Counter of DNS lookups */
+	unsigned int		debug_id;
 
 	/* The volumes belonging to this cell */
 	struct rb_root		volumes;	/* Tree of volumes on this server */
@@ -917,11 +920,16 @@ static inline bool afs_cb_is_broken(unsigned int cb_break,
  * cell.c
  */
 extern int afs_cell_init(struct afs_net *, const char *);
-extern struct afs_cell *afs_lookup_cell_rcu(struct afs_net *, const char *, unsigned);
+extern struct afs_cell *afs_find_cell(struct afs_net *, const char *, unsigned,
+				      enum afs_cell_trace);
 extern struct afs_cell *afs_lookup_cell(struct afs_net *, const char *, unsigned,
 					const char *, bool);
-extern struct afs_cell *afs_get_cell(struct afs_cell *);
-extern void afs_put_cell(struct afs_net *, struct afs_cell *);
+extern struct afs_cell *afs_use_cell(struct afs_cell *, enum afs_cell_trace);
+extern void afs_unuse_cell(struct afs_net *, struct afs_cell *, enum afs_cell_trace);
+extern struct afs_cell *afs_get_cell(struct afs_cell *, enum afs_cell_trace);
+extern void afs_see_cell(struct afs_cell *, enum afs_cell_trace);
+extern void afs_put_cell(struct afs_cell *, enum afs_cell_trace);
+extern void afs_queue_cell(struct afs_cell *, enum afs_cell_trace);
 extern void afs_manage_cells(struct work_struct *);
 extern void afs_cells_timer(struct timer_list *);
 extern void __net_exit afs_cell_purge(struct afs_net *);
diff --git a/fs/afs/main.c b/fs/afs/main.c
index 31b472f7c734..accdd8970e7c 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -78,7 +78,7 @@ static int __net_init afs_net_init(struct net *net_ns)
 	mutex_init(&net->socket_mutex);
 
 	net->cells = RB_ROOT;
-	seqlock_init(&net->cells_lock);
+	init_rwsem(&net->cells_lock);
 	INIT_WORK(&net->cells_manager, afs_manage_cells);
 	timer_setup(&net->cells_timer, afs_cells_timer, 0);
 
diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
index 79bc5f1338ed..052dab2f5c03 100644
--- a/fs/afs/mntpt.c
+++ b/fs/afs/mntpt.c
@@ -88,7 +88,7 @@ static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
 		ctx->force = true;
 	}
 	if (ctx->cell) {
-		afs_put_cell(ctx->net, ctx->cell);
+		afs_unuse_cell(ctx->net, ctx->cell, afs_cell_trace_unuse_mntpt);
 		ctx->cell = NULL;
 	}
 	if (test_bit(AFS_VNODE_PSEUDODIR, &vnode->flags)) {
@@ -124,7 +124,7 @@ static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
 		char *buf;
 
 		if (src_as->cell)
-			ctx->cell = afs_get_cell(src_as->cell);
+			ctx->cell = afs_use_cell(src_as->cell, afs_cell_trace_use_mntpt);
 
 		if (size < 2 || size > PAGE_SIZE - 1)
 			return -EINVAL;
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index e8babb62ed44..065a28bfa3f1 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -38,7 +38,7 @@ static int afs_proc_cells_show(struct seq_file *m, void *v)
 
 	if (v == SEQ_START_TOKEN) {
 		/* display header on line 1 */
-		seq_puts(m, "USE    TTL SV ST NAME\n");
+		seq_puts(m, "USE ACT    TTL SV ST NAME\n");
 		return 0;
 	}
 
@@ -46,10 +46,11 @@ static int afs_proc_cells_show(struct seq_file *m, void *v)
 	vllist = rcu_dereference(cell->vl_servers);
 
 	/* display one cell per line on subsequent lines */
-	seq_printf(m, "%3u %6lld %2u %2u %s\n",
-		   atomic_read(&cell->usage),
+	seq_printf(m, "%3u %3u %6lld %2u %2u %s\n",
+		   atomic_read(&cell->ref),
+		   atomic_read(&cell->active),
 		   cell->dns_expiry - ktime_get_real_seconds(),
-		   vllist->nr_servers,
+		   vllist ? vllist->nr_servers : 0,
 		   cell->state,
 		   cell->name);
 	return 0;
@@ -128,7 +129,7 @@ static int afs_proc_cells_write(struct file *file, char *buf, size_t size)
 		}
 
 		if (test_and_set_bit(AFS_CELL_FL_NO_GC, &cell->flags))
-			afs_put_cell(net, cell);
+			afs_unuse_cell(net, cell, afs_cell_trace_unuse_no_pin);
 	} else {
 		goto inval;
 	}
@@ -154,13 +155,11 @@ static int afs_proc_rootcell_show(struct seq_file *m, void *v)
 	struct afs_net *net;
 
 	net = afs_seq2net_single(m);
-	if (rcu_access_pointer(net->ws_cell)) {
-		rcu_read_lock();
-		cell = rcu_dereference(net->ws_cell);
-		if (cell)
-			seq_printf(m, "%s\n", cell->name);
-		rcu_read_unlock();
-	}
+	down_read(&net->cells_lock);
+	cell = net->ws_cell;
+	if (cell)
+		seq_printf(m, "%s\n", cell->name);
+	up_read(&net->cells_lock);
 	return 0;
 }
 
diff --git a/fs/afs/server.c b/fs/afs/server.c
index e82e452e2612..684a2b02b9ff 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -550,7 +550,12 @@ void afs_manage_servers(struct work_struct *work)
 
 		_debug("manage %pU %u", &server->uuid, active);
 
-		ASSERTIFCMP(purging, active, ==, 0);
+		if (purging) {
+			trace_afs_server(server, atomic_read(&server->ref),
+					 active, afs_server_trace_purging);
+			if (active != 0)
+				pr_notice("Can't purge s=%08x\n", server->debug_id);
+		}
 
 		if (active == 0) {
 			time64_t expire_at = server->unuse_time;
diff --git a/fs/afs/super.c b/fs/afs/super.c
index 3a40ee752c1e..6c5900df6aa5 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -294,7 +294,8 @@ static int afs_parse_source(struct fs_context *fc, struct fs_parameter *param)
 			       cellnamesz, cellnamesz, cellname ?: "");
 			return PTR_ERR(cell);
 		}
-		afs_put_cell(ctx->net, ctx->cell);
+		afs_unuse_cell(ctx->net, ctx->cell, afs_cell_trace_unuse_parse);
+		afs_see_cell(cell, afs_cell_trace_see_source);
 		ctx->cell = cell;
 	}
 
@@ -389,8 +390,9 @@ static int afs_validate_fc(struct fs_context *fc)
 				_debug("switch to alias");
 				key_put(ctx->key);
 				ctx->key = NULL;
-				cell = afs_get_cell(ctx->cell->alias_of);
-				afs_put_cell(ctx->net, ctx->cell);
+				cell = afs_use_cell(ctx->cell->alias_of,
+						    afs_cell_trace_use_fc_alias);
+				afs_unuse_cell(ctx->net, ctx->cell, afs_cell_trace_unuse_fc);
 				ctx->cell = cell;
 				goto reget_key;
 			}
@@ -507,7 +509,7 @@ static struct afs_super_info *afs_alloc_sbi(struct fs_context *fc)
 		if (ctx->dyn_root) {
 			as->dyn_root = true;
 		} else {
-			as->cell = afs_get_cell(ctx->cell);
+			as->cell = afs_use_cell(ctx->cell, afs_cell_trace_use_sbi);
 			as->volume = afs_get_volume(ctx->volume,
 						    afs_volume_trace_get_alloc_sbi);
 		}
@@ -520,7 +522,7 @@ static void afs_destroy_sbi(struct afs_super_info *as)
 	if (as) {
 		struct afs_net *net = afs_net(as->net_ns);
 		afs_put_volume(net, as->volume, afs_volume_trace_put_destroy_sbi);
-		afs_put_cell(net, as->cell);
+		afs_unuse_cell(net, as->cell, afs_cell_trace_unuse_sbi);
 		put_net(as->net_ns);
 		kfree(as);
 	}
@@ -606,7 +608,7 @@ static void afs_free_fc(struct fs_context *fc)
 
 	afs_destroy_sbi(fc->s_fs_info);
 	afs_put_volume(ctx->net, ctx->volume, afs_volume_trace_put_free_fc);
-	afs_put_cell(ctx->net, ctx->cell);
+	afs_unuse_cell(ctx->net, ctx->cell, afs_cell_trace_unuse_fc);
 	key_put(ctx->key);
 	kfree(ctx);
 }
@@ -633,9 +635,7 @@ static int afs_init_fs_context(struct fs_context *fc)
 	ctx->net = afs_net(fc->net_ns);
 
 	/* Default to the workstation cell. */
-	rcu_read_lock();
-	cell = afs_lookup_cell_rcu(ctx->net, NULL, 0);
-	rcu_read_unlock();
+	cell = afs_find_cell(ctx->net, NULL, 0, afs_cell_trace_use_fc);
 	if (IS_ERR(cell))
 		cell = NULL;
 	ctx->cell = cell;
diff --git a/fs/afs/vl_alias.c b/fs/afs/vl_alias.c
index 5082ef04e99c..f04a80e4f5c3 100644
--- a/fs/afs/vl_alias.c
+++ b/fs/afs/vl_alias.c
@@ -177,7 +177,7 @@ static int afs_compare_cell_roots(struct afs_cell *cell)
 
 is_alias:
 	rcu_read_unlock();
-	cell->alias_of = afs_get_cell(p);
+	cell->alias_of = afs_use_cell(p, afs_cell_trace_use_alias);
 	return 1;
 }
 
@@ -247,18 +247,18 @@ static int afs_query_for_alias(struct afs_cell *cell, struct key *key)
 			continue;
 		if (p->root_volume)
 			continue; /* Ignore cells that have a root.cell volume. */
-		afs_get_cell(p);
+		afs_use_cell(p, afs_cell_trace_use_check_alias);
 		mutex_unlock(&cell->net->proc_cells_lock);
 
 		if (afs_query_for_alias_one(cell, key, p) != 0)
 			goto is_alias;
 
 		if (mutex_lock_interruptible(&cell->net->proc_cells_lock) < 0) {
-			afs_put_cell(cell->net, p);
+			afs_unuse_cell(cell->net, p, afs_cell_trace_unuse_check_alias);
 			return -ERESTARTSYS;
 		}
 
-		afs_put_cell(cell->net, p);
+		afs_unuse_cell(cell->net, p, afs_cell_trace_unuse_check_alias);
 	}
 
 	mutex_unlock(&cell->net->proc_cells_lock);
diff --git a/fs/afs/vl_rotate.c b/fs/afs/vl_rotate.c
index c0458c903b31..488e58490b16 100644
--- a/fs/afs/vl_rotate.c
+++ b/fs/afs/vl_rotate.c
@@ -45,7 +45,7 @@ static bool afs_start_vl_iteration(struct afs_vl_cursor *vc)
 	    cell->dns_expiry <= ktime_get_real_seconds()) {
 		dns_lookup_count = smp_load_acquire(&cell->dns_lookup_count);
 		set_bit(AFS_CELL_FL_DO_LOOKUP, &cell->flags);
-		queue_work(afs_wq, &cell->manager);
+		afs_queue_cell(cell, afs_cell_trace_get_queue_dns);
 
 		if (cell->dns_source == DNS_RECORD_UNAVAILABLE) {
 			if (wait_var_event_interruptible(
diff --git a/fs/afs/volume.c b/fs/afs/volume.c
index 9bc0509e3634..f84194b791d3 100644
--- a/fs/afs/volume.c
+++ b/fs/afs/volume.c
@@ -83,7 +83,7 @@ static struct afs_volume *afs_alloc_volume(struct afs_fs_context *params,
 
 	volume->vid		= vldb->vid[params->type];
 	volume->update_at	= ktime_get_real_seconds() + afs_volume_record_life;
-	volume->cell		= afs_get_cell(params->cell);
+	volume->cell		= afs_get_cell(params->cell, afs_cell_trace_get_vol);
 	volume->type		= params->type;
 	volume->type_force	= params->force;
 	volume->name_len	= vldb->name_len;
@@ -106,7 +106,7 @@ static struct afs_volume *afs_alloc_volume(struct afs_fs_context *params,
 	return volume;
 
 error_1:
-	afs_put_cell(params->net, volume->cell);
+	afs_put_cell(volume->cell, afs_cell_trace_put_vol);
 	kfree(volume);
 error_0:
 	return ERR_PTR(ret);
@@ -228,7 +228,7 @@ static void afs_destroy_volume(struct afs_net *net, struct afs_volume *volume)
 
 	afs_remove_volume_from_cell(volume);
 	afs_put_serverlist(net, rcu_access_pointer(volume->servers));
-	afs_put_cell(net, volume->cell);
+	afs_put_cell(volume->cell, afs_cell_trace_put_vol);
 	trace_afs_volume(volume->vid, atomic_read(&volume->usage),
 			 afs_volume_trace_free);
 	kfree_rcu(volume, rcu);
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index 5f0c1cf1ea13..8eb49231c6bb 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -40,6 +40,7 @@ enum afs_server_trace {
 	afs_server_trace_get_new_cbi,
 	afs_server_trace_get_probe,
 	afs_server_trace_give_up_cb,
+	afs_server_trace_purging,
 	afs_server_trace_put_call,
 	afs_server_trace_put_cbi,
 	afs_server_trace_put_find_rsq,
@@ -50,6 +51,7 @@ enum afs_server_trace {
 	afs_server_trace_update,
 };
 
+
 enum afs_volume_trace {
 	afs_volume_trace_alloc,
 	afs_volume_trace_free,
@@ -67,6 +69,46 @@ enum afs_volume_trace {
 	afs_volume_trace_remove,
 };
 
+enum afs_cell_trace {
+	afs_cell_trace_alloc,
+	afs_cell_trace_free,
+	afs_cell_trace_get_queue_dns,
+	afs_cell_trace_get_queue_manage,
+	afs_cell_trace_get_queue_new,
+	afs_cell_trace_get_vol,
+	afs_cell_trace_insert,
+	afs_cell_trace_manage,
+	afs_cell_trace_put_candidate,
+	afs_cell_trace_put_destroy,
+	afs_cell_trace_put_queue_fail,
+	afs_cell_trace_put_queue_work,
+	afs_cell_trace_put_vol,
+	afs_cell_trace_see_source,
+	afs_cell_trace_see_ws,
+	afs_cell_trace_unuse_alias,
+	afs_cell_trace_unuse_check_alias,
+	afs_cell_trace_unuse_delete,
+	afs_cell_trace_unuse_fc,
+	afs_cell_trace_unuse_lookup,
+	afs_cell_trace_unuse_mntpt,
+	afs_cell_trace_unuse_no_pin,
+	afs_cell_trace_unuse_parse,
+	afs_cell_trace_unuse_pin,
+	afs_cell_trace_unuse_probe,
+	afs_cell_trace_unuse_sbi,
+	afs_cell_trace_unuse_ws,
+	afs_cell_trace_use_alias,
+	afs_cell_trace_use_check_alias,
+	afs_cell_trace_use_fc,
+	afs_cell_trace_use_fc_alias,
+	afs_cell_trace_use_lookup,
+	afs_cell_trace_use_mntpt,
+	afs_cell_trace_use_pin,
+	afs_cell_trace_use_probe,
+	afs_cell_trace_use_sbi,
+	afs_cell_trace_wait,
+};
+
 enum afs_fs_operation {
 	afs_FS_FetchData		= 130,	/* AFS Fetch file data */
 	afs_FS_FetchACL			= 131,	/* AFS Fetch file ACL */
@@ -270,6 +312,7 @@ enum afs_cb_break_reason {
 	EM(afs_server_trace_get_new_cbi,	"GET cbi  ") \
 	EM(afs_server_trace_get_probe,		"GET probe") \
 	EM(afs_server_trace_give_up_cb,		"giveup-cb") \
+	EM(afs_server_trace_purging,		"PURGE    ") \
 	EM(afs_server_trace_put_call,		"PUT call ") \
 	EM(afs_server_trace_put_cbi,		"PUT cbi  ") \
 	EM(afs_server_trace_put_find_rsq,	"PUT f-rsq") \
@@ -295,6 +338,44 @@ enum afs_cb_break_reason {
 	EM(afs_volume_trace_put_validate_fc,	"PUT fc-validat") \
 	E_(afs_volume_trace_remove,		"REMOVE        ")
 
+#define afs_cell_traces \
+	EM(afs_cell_trace_alloc,		"ALLOC     ") \
+	EM(afs_cell_trace_free,			"FREE      ") \
+	EM(afs_cell_trace_get_queue_dns,	"GET q-dns ") \
+	EM(afs_cell_trace_get_queue_manage,	"GET q-mng ") \
+	EM(afs_cell_trace_get_queue_new,	"GET q-new ") \
+	EM(afs_cell_trace_get_vol,		"GET vol   ") \
+	EM(afs_cell_trace_insert,		"INSERT    ") \
+	EM(afs_cell_trace_manage,		"MANAGE    ") \
+	EM(afs_cell_trace_put_candidate,	"PUT candid") \
+	EM(afs_cell_trace_put_destroy,		"PUT destry") \
+	EM(afs_cell_trace_put_queue_work,	"PUT q-work") \
+	EM(afs_cell_trace_put_queue_fail,	"PUT q-fail") \
+	EM(afs_cell_trace_put_vol,		"PUT vol   ") \
+	EM(afs_cell_trace_see_source,		"SEE source") \
+	EM(afs_cell_trace_see_ws,		"SEE ws    ") \
+	EM(afs_cell_trace_unuse_alias,		"UNU alias ") \
+	EM(afs_cell_trace_unuse_check_alias,	"UNU chk-al") \
+	EM(afs_cell_trace_unuse_delete,		"UNU delete") \
+	EM(afs_cell_trace_unuse_fc,		"UNU fc    ") \
+	EM(afs_cell_trace_unuse_lookup,		"UNU lookup") \
+	EM(afs_cell_trace_unuse_mntpt,		"UNU mntpt ") \
+	EM(afs_cell_trace_unuse_parse,		"UNU parse ") \
+	EM(afs_cell_trace_unuse_pin,		"UNU pin   ") \
+	EM(afs_cell_trace_unuse_probe,		"UNU probe ") \
+	EM(afs_cell_trace_unuse_sbi,		"UNU sbi   ") \
+	EM(afs_cell_trace_unuse_ws,		"UNU ws    ") \
+	EM(afs_cell_trace_use_alias,		"USE alias ") \
+	EM(afs_cell_trace_use_check_alias,	"USE chk-al") \
+	EM(afs_cell_trace_use_fc,		"USE fc    ") \
+	EM(afs_cell_trace_use_fc_alias,		"USE fc-al ") \
+	EM(afs_cell_trace_use_lookup,		"USE lookup") \
+	EM(afs_cell_trace_use_mntpt,		"USE mntpt ") \
+	EM(afs_cell_trace_use_pin,		"USE pin   ") \
+	EM(afs_cell_trace_use_probe,		"USE probe ") \
+	EM(afs_cell_trace_use_sbi,		"USE sbi   ") \
+	E_(afs_cell_trace_wait,			"WAIT      ")
+
 #define afs_fs_operations \
 	EM(afs_FS_FetchData,			"FS.FetchData") \
 	EM(afs_FS_FetchStatus,			"FS.FetchStatus") \
@@ -483,6 +564,7 @@ enum afs_cb_break_reason {
 
 afs_call_traces;
 afs_server_traces;
+afs_cell_traces;
 afs_fs_operations;
 afs_vl_operations;
 afs_edit_dir_ops;
@@ -1358,6 +1440,33 @@ TRACE_EVENT(afs_volume,
 		      __entry->ref)
 	    );
 
+TRACE_EVENT(afs_cell,
+	    TP_PROTO(unsigned int cell_debug_id, int usage, int active,
+		     enum afs_cell_trace reason),
+
+	    TP_ARGS(cell_debug_id, usage, active, reason),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,		cell		)
+		    __field(int,			usage		)
+		    __field(int,			active		)
+		    __field(int,			reason		)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->cell = cell_debug_id;
+		    __entry->usage = usage;
+		    __entry->active = active;
+		    __entry->reason = reason;
+			   ),
+
+	    TP_printk("L=%08x %s u=%d a=%d",
+		      __entry->cell,
+		      __print_symbolic(__entry->reason, afs_cell_traces),
+		      __entry->usage,
+		      __entry->active)
+	    );
+
 #endif /* _TRACE_AFS_H */
 
 /* This part must be outside protection */