Re: [PATCH] binderfs: rework superblock destruction

From: Christian Brauner
Date: Wed Aug 17 2022 - 10:51:59 EST


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"?

I think at least these below. Completely untested...

Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
---
arch/s390/hypfs/inode.c | 3 +--
fs/devpts/inode.c | 2 +-
fs/ramfs/inode.c | 4 +++-
security/selinux/selinuxfs.c | 12 ++++++------
4 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/s390/hypfs/inode.c b/arch/s390/hypfs/inode.c
index 5c97f48cea91..d7d275ef132f 100644
--- a/arch/s390/hypfs/inode.c
+++ b/arch/s390/hypfs/inode.c
@@ -329,9 +329,8 @@ static void hypfs_kill_super(struct super_block *sb)
hypfs_delete_tree(sb->s_root);
if (sb_info && sb_info->update_file)
hypfs_remove(sb_info->update_file);
- kfree(sb->s_fs_info);
- sb->s_fs_info = NULL;
kill_litter_super(sb);
+ kfree(sb->s_fs_info);
}

static struct dentry *hypfs_create_file(struct dentry *parent, const char *name,
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 4f25015aa534..78a9095e1748 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -509,10 +509,10 @@ static void devpts_kill_sb(struct super_block *sb)
{
struct pts_fs_info *fsi = DEVPTS_SB(sb);

+ kill_litter_super(sb);
if (fsi)
ida_destroy(&fsi->allocated_ptys);
kfree(fsi);
- kill_litter_super(sb);
}

static struct file_system_type devpts_fs_type = {
diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index bc66d0173e33..bff49294e037 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -280,8 +280,10 @@ int ramfs_init_fs_context(struct fs_context *fc)

static void ramfs_kill_sb(struct super_block *sb)
{
- kfree(sb->s_fs_info);
+ struct ramfs_fs_info *fsi = sb->s_fs_info;
+
kill_litter_super(sb);
+ kfree(fsi);
}

static struct file_system_type ramfs_fs_type = {
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 8fcdd494af27..fb1dae422d93 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -96,9 +96,8 @@ static int selinux_fs_info_create(struct super_block *sb)
return 0;
}

-static void selinux_fs_info_free(struct super_block *sb)
+static void selinux_fs_info_free(struct selinux_fs_info *fsi)
{
- struct selinux_fs_info *fsi = sb->s_fs_info;
int i;

if (fsi) {
@@ -107,8 +106,7 @@ static void selinux_fs_info_free(struct super_block *sb)
kfree(fsi->bool_pending_names);
kfree(fsi->bool_pending_values);
}
- kfree(sb->s_fs_info);
- sb->s_fs_info = NULL;
+ kfree(fsi);
}

#define SEL_INITCON_INO_OFFSET 0x01000000
@@ -2180,7 +2178,7 @@ static int sel_fill_super(struct super_block *sb, struct fs_context *fc)
pr_err("SELinux: %s: failed while creating inodes\n",
__func__);

- selinux_fs_info_free(sb);
+ selinux_fs_info_free(fsi);

return ret;
}
@@ -2202,8 +2200,10 @@ static int sel_init_fs_context(struct fs_context *fc)

static void sel_kill_sb(struct super_block *sb)
{
- selinux_fs_info_free(sb);
+ struct selinux_fs_info *fsi = sb->s_fs_info;
+
kill_litter_super(sb);
+ selinux_fs_info_free(fsi);
}

static struct file_system_type sel_fs_type = {
--
2.34.1