afs: Defer volume record destruction to a workqueue

Defer volume record destruction to a workqueue so that afs_put_volume()
isn't going to run the destruction process in the callback workqueue whilst
the server is holding up other clients whilst waiting for us to reply to a
CB.CallBack notification RPC.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

fs/afs/cell.c

@@ -818,7 +818,7 @@ static void afs_manage_cell(struct afs_cell *cell)
 
 final_destruction:
 	/* The root volume is pinning the cell */
-	afs_put_volume(cell->net, cell->root_volume, afs_volume_trace_put_cell_root);
+	afs_put_volume(cell->root_volume, afs_volume_trace_put_cell_root);
 	cell->root_volume = NULL;
 	afs_put_cell(cell, afs_cell_trace_put_destroy);
 }

fs/afs/fs_operation.c

@@ -265,7 +265,7 @@ int afs_put_operation(struct afs_operation *op)
 	}
 
 	afs_put_serverlist(op->net, op->server_list);
-	afs_put_volume(op->net, op->volume, afs_volume_trace_put_put_op);
+	afs_put_volume(op->volume, afs_volume_trace_put_put_op);
 	key_put(op->key);
 	kfree(op);
 	return ret;

fs/afs/internal.h

@@ -636,6 +636,7 @@ struct afs_volume {
 	struct rb_node		cell_node;	/* Link in cell->volumes */
 	struct hlist_node	proc_link;	/* Link in cell->proc_volumes */
 	struct super_block __rcu *sb;		/* Superblock on which inodes reside */
+	struct work_struct	destructor;	/* Deferred destructor */
 	unsigned long		flags;
 #define AFS_VOLUME_NEEDS_UPDATE	0	/* - T if an update needs performing */
 #define AFS_VOLUME_UPDATING	1	/* - T if an update is in progress */
@@ -1613,7 +1614,7 @@ extern int afs_activate_volume(struct afs_volume *);
 extern void afs_deactivate_volume(struct afs_volume *);
 bool afs_try_get_volume(struct afs_volume *volume, enum afs_volume_trace reason);
 extern struct afs_volume *afs_get_volume(struct afs_volume *, enum afs_volume_trace);
-extern void afs_put_volume(struct afs_net *, struct afs_volume *, enum afs_volume_trace);
+void afs_put_volume(struct afs_volume *volume, enum afs_volume_trace reason);
 extern int afs_check_volume_status(struct afs_volume *, struct afs_operation *);
 
 /*

fs/afs/super.c

@@ -381,8 +381,7 @@ static int afs_validate_fc(struct fs_context *fc)
 		ctx->key = key;
 
 		if (ctx->volume) {
-			afs_put_volume(ctx->net, ctx->volume,
-				       afs_volume_trace_put_validate_fc);
+			afs_put_volume(ctx->volume, afs_volume_trace_put_validate_fc);
 			ctx->volume = NULL;
 		}
 
@@ -529,7 +528,7 @@ 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_volume(as->volume, afs_volume_trace_put_destroy_sbi);
 		afs_unuse_cell(net, as->cell, afs_cell_trace_unuse_sbi);
 		put_net(as->net_ns);
 		kfree(as);
@@ -615,7 +614,7 @@ static void afs_free_fc(struct fs_context *fc)
 	struct afs_fs_context *ctx = fc->fs_private;
 
 	afs_destroy_sbi(fc->s_fs_info);
-	afs_put_volume(ctx->net, ctx->volume, afs_volume_trace_put_free_fc);
+	afs_put_volume(ctx->volume, afs_volume_trace_put_free_fc);
 	afs_unuse_cell(ctx->net, ctx->cell, afs_cell_trace_unuse_fc);
 	key_put(ctx->key);
 	kfree(ctx);

fs/afs/vl_alias.c

@@ -156,7 +156,7 @@ static int afs_query_for_alias_one(struct afs_cell *cell, struct key *key,
 	/* And see if it's in the new cell. */
 	volume = afs_sample_volume(cell, key, pvol->name, pvol->name_len);
 	if (IS_ERR(volume)) {
-		afs_put_volume(cell->net, pvol, afs_volume_trace_put_query_alias);
+		afs_put_volume(pvol, afs_volume_trace_put_query_alias);
 		if (PTR_ERR(volume) != -ENOMEDIUM)
 			return PTR_ERR(volume);
 		/* That volume is not in the new cell, so not an alias */
@@ -174,8 +174,8 @@ static int afs_query_for_alias_one(struct afs_cell *cell, struct key *key,
 		rcu_read_unlock();
 	}
 
-	afs_put_volume(cell->net, volume, afs_volume_trace_put_query_alias);
-	afs_put_volume(cell->net, pvol, afs_volume_trace_put_query_alias);
+	afs_put_volume(volume, afs_volume_trace_put_query_alias);
+	afs_put_volume(pvol, afs_volume_trace_put_query_alias);
 	return ret;
 }
 

fs/afs/volume.c

@@ -11,6 +11,8 @@
 
 static unsigned __read_mostly afs_volume_record_life = 60 * 60;
 
+static void afs_destroy_volume(struct work_struct *work);
+
 /*
  * Insert a volume into a cell.  If there's an existing volume record, that is
  * returned instead with a ref held.
@@ -91,6 +93,7 @@ static struct afs_volume *afs_alloc_volume(struct afs_fs_context *params,
 
 	refcount_set(&volume->ref, 1);
 	INIT_HLIST_NODE(&volume->proc_link);
+	INIT_WORK(&volume->destructor, afs_destroy_volume);
 	rwlock_init(&volume->servers_lock);
 	rwlock_init(&volume->cb_v_break_lock);
 	memcpy(volume->name, vldb->name, vldb->name_len + 1);
@@ -133,7 +136,7 @@ static struct afs_volume *afs_lookup_volume(struct afs_fs_context *params,
 	if (volume == candidate)
 		afs_attach_volume_to_servers(volume, slist);
 	else
-		afs_put_volume(params->net, candidate, afs_volume_trace_put_cell_dup);
+		afs_put_volume(candidate, afs_volume_trace_put_cell_dup);
 	return volume;
 }
 
@@ -223,8 +226,9 @@ struct afs_volume *afs_create_volume(struct afs_fs_context *params)
 /*
  * Destroy a volume record
  */
-static void afs_destroy_volume(struct afs_net *net, struct afs_volume *volume)
+static void afs_destroy_volume(struct work_struct *work)
 {
+	struct afs_volume *volume = container_of(work, struct afs_volume, destructor);
 	struct afs_server_list *slist = rcu_access_pointer(volume->servers);
 
 	_enter("%p", volume);
@@ -235,7 +239,7 @@ static void afs_destroy_volume(struct afs_net *net, struct afs_volume *volume)
 
 	afs_detach_volume_from_servers(volume, slist);
 	afs_remove_volume_from_cell(volume);
-	afs_put_serverlist(net, slist);
+	afs_put_serverlist(volume->cell->net, slist);
 	afs_put_cell(volume->cell, afs_cell_trace_put_vol);
 	trace_afs_volume(volume->vid, refcount_read(&volume->ref),
 			 afs_volume_trace_free);
@@ -277,8 +281,7 @@ struct afs_volume *afs_get_volume(struct afs_volume *volume,
 /*
  * Drop a reference on a volume record.
  */
-void afs_put_volume(struct afs_net *net, struct afs_volume *volume,
-		    enum afs_volume_trace reason)
+void afs_put_volume(struct afs_volume *volume, enum afs_volume_trace reason)
 {
 	if (volume) {
 		afs_volid_t vid = volume->vid;
@@ -288,7 +291,7 @@ void afs_put_volume(struct afs_net *net, struct afs_volume *volume,
 		zero = __refcount_dec_and_test(&volume->ref, &r);
 		trace_afs_volume(vid, r - 1, reason);
 		if (zero)
-			afs_destroy_volume(net, volume);
+			schedule_work(&volume->destructor);
 	}
 }