afs: Fix cell proc list

Access to the list of cells by /proc/net/afs/cells has a couple of
problems:

 (1) It should be checking against SEQ_START_TOKEN for the keying the
     header line.

 (2) It's only holding the RCU read lock, so it can't just walk over the
     list without following the proper RCU methods.

Fix these by using an hlist instead of an ordinary list and using the
appropriate accessor functions to follow it with RCU.

Since the code that adds a cell to the list must also necessarily change,
sort the list on insertion whilst we're at it.

Fixes: 989782dc ("afs: Overhaul cell database management")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/afs/cell.c

@@ -514,6 +514,8 @@ static int afs_alloc_anon_key(struct afs_cell *cell)
  */
 static int afs_activate_cell(struct afs_net *net, struct afs_cell *cell)
 {
+	struct hlist_node **p;
+	struct afs_cell *pcell;
 	int ret;
 
 	if (!cell->anonymous_key) {
@@ -534,7 +536,18 @@ static int afs_activate_cell(struct afs_net *net, struct afs_cell *cell)
 		return ret;
 
 	mutex_lock(&net->proc_cells_lock);
-	list_add_tail(&cell->proc_link, &net->proc_cells);
+	for (p = &net->proc_cells.first; *p; p = &(*p)->next) {
+		pcell = hlist_entry(*p, struct afs_cell, proc_link);
+		if (strcmp(cell->name, pcell->name) < 0)
+			break;
+	}
+
+	cell->proc_link.pprev = p;
+	cell->proc_link.next = *p;
+	rcu_assign_pointer(*p, &cell->proc_link.next);
+	if (cell->proc_link.next)
+		cell->proc_link.next->pprev = &cell->proc_link.next;
+
 	afs_dynroot_mkdir(net, cell);
 	mutex_unlock(&net->proc_cells_lock);
 	return 0;
@@ -550,7 +563,7 @@ static void afs_deactivate_cell(struct afs_net *net, struct afs_cell *cell)
 	afs_proc_cell_remove(cell);
 
 	mutex_lock(&net->proc_cells_lock);
-	list_del_init(&cell->proc_link);
+	hlist_del_rcu(&cell->proc_link);
 	afs_dynroot_rmdir(net, cell);
 	mutex_unlock(&net->proc_cells_lock);
 

fs/afs/dynroot.c

@@ -265,7 +265,7 @@ int afs_dynroot_populate(struct super_block *sb)
 		return -ERESTARTSYS;
 
 	net->dynroot_sb = sb;
-	list_for_each_entry(cell, &net->proc_cells, proc_link) {
+	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
 		ret = afs_dynroot_mkdir(net, cell);
 		if (ret < 0)
 			goto error;

fs/afs/internal.h

@@ -242,7 +242,7 @@ struct afs_net {
 	seqlock_t		cells_lock;
 
 	struct mutex		proc_cells_lock;
-	struct list_head	proc_cells;
+	struct hlist_head	proc_cells;
 
 	/* Known servers.  Theoretically each fileserver can only be in one
 	 * cell, but in practice, people create aliases and subsets and there's
@@ -320,7 +320,7 @@ struct afs_cell {
 	struct afs_net		*net;
 	struct key		*anonymous_key;	/* anonymous user key for this cell */
 	struct work_struct	manager;	/* Manager for init/deinit/dns */
-	struct list_head	proc_link;	/* /proc cell list link */
+	struct hlist_node	proc_link;	/* /proc cell list link */
 #ifdef CONFIG_AFS_FSCACHE
 	struct fscache_cookie	*cache;		/* caching cookie */
 #endif

fs/afs/main.c

@@ -87,7 +87,7 @@ static int __net_init afs_net_init(struct net *net_ns)
 	timer_setup(&net->cells_timer, afs_cells_timer, 0);
 
 	mutex_init(&net->proc_cells_lock);
-	INIT_LIST_HEAD(&net->proc_cells);
+	INIT_HLIST_HEAD(&net->proc_cells);
 
 	seqlock_init(&net->fs_lock);
 	net->fs_servers = RB_ROOT;

fs/afs/proc.c

@@ -33,9 +33,8 @@ static inline struct afs_net *afs_seq2net_single(struct seq_file *m)
 static int afs_proc_cells_show(struct seq_file *m, void *v)
 {
 	struct afs_cell *cell = list_entry(v, struct afs_cell, proc_link);
-	struct afs_net *net = afs_seq2net(m);
 
-	if (v == &net->proc_cells) {
+	if (v == SEQ_START_TOKEN) {
 		/* display header on line 1 */
 		seq_puts(m, "USE NAME\n");
 		return 0;
@@ -50,12 +49,12 @@ static void *afs_proc_cells_start(struct seq_file *m, loff_t *_pos)
 	__acquires(rcu)
 {
 	rcu_read_lock();
-	return seq_list_start_head(&afs_seq2net(m)->proc_cells, *_pos);
+	return seq_hlist_start_head_rcu(&afs_seq2net(m)->proc_cells, *_pos);
 }
 
 static void *afs_proc_cells_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	return seq_list_next(v, &afs_seq2net(m)->proc_cells, pos);
+	return seq_hlist_next_rcu(v, &afs_seq2net(m)->proc_cells, pos);
 }
 
 static void afs_proc_cells_stop(struct seq_file *m, void *v)