Messages in this thread | | | Date | Wed, 17 Aug 2022 15:32:03 +0100 | From | Al Viro <> | Subject | Re: [PATCH] binderfs: rework superblock destruction |
| |
On Wed, Aug 17, 2022 at 03:19:13PM +0100, Al Viro wrote: > On Wed, Aug 17, 2022 at 04:01:49PM +0200, Christian Brauner wrote: > > On Wed, Aug 17, 2022 at 02:59:02PM +0100, Al Viro wrote: > > > On Wed, Aug 17, 2022 at 03:03:06PM +0200, Christian Brauner wrote: > > > > > > > +static void binderfs_kill_super(struct super_block *sb) > > > > +{ > > > > + struct binderfs_info *info = sb->s_fs_info; > > > > + > > > > + if (info && info->ipc_ns) > > > > + put_ipc_ns(info->ipc_ns); > > > > + > > > > + kfree(info); > > > > + kill_litter_super(sb); > > > > +} > > > > > > Other way round, please - shut the superblock down, *then* > > > free the objects it'd been using. IOW, > > > > I wondered about that but a lot of places do it the other way around. > > So maybe the expected order should be documented somewhere. > > ??? > > "If you are holding internal references to dentries/inodes/etc., drop them > first; if you are going to free something that is used by filesystem > methods, don't do that before the filesystem is shut down" > > That's just common sense... Which filesystems are doing that "the other > way around"?
Note that something like e.g. ramfs, where we have a dynamically allocated object ->s_fs_info is pointing to and gets freed early in their ->kill_sb() is somewhat misleading - it's used only for two things, one is the creation of root directory inode (obviously not going to happen at any point after mount) and another - ->show_options(). By the point we get around to killing a superblock, it would better *NOT* have mounts pointing to it that might show up in /proc/mounts and make us call ->show_options().
So there we really know that nothing during the shutdown will even look at that thing we'd just freed. Not that there'd ever been a point allocating it - all that object contains is one unsigned short, so we might as well just have stored (void *)root_mode in ->s_fs_info. Oh, well...
| |