On Tue, May 02, 2023 at 03:38:46PM +0200, Michal Koutný wrote: > The function current_cgns_cgroup_from_root() expects a stable > cgroup_root, which is currently ensured with RCU read side paired with > cgroup_destroy_root() called after RCU period. > > The particular current_cgns_cgroup_from_root() is called from VFS code > and cgroup_root stability can be also ensured by namespace_sem. Mark it > explicitly as a preparation for further rework. > > Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx> > --- > fs/namespace.c | 5 ++++- > include/linux/mount.h | 4 ++++ > kernel/cgroup/cgroup.c | 7 +++---- > 3 files changed, 11 insertions(+), 5 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 54847db5b819..0d2333832064 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -71,7 +71,10 @@ static DEFINE_IDA(mnt_group_ida); > static struct hlist_head *mount_hashtable __read_mostly; > static struct hlist_head *mountpoint_hashtable __read_mostly; > static struct kmem_cache *mnt_cache __read_mostly; > -static DECLARE_RWSEM(namespace_sem); > +DECLARE_RWSEM(namespace_sem); > +#ifdef CONFIG_LOCKDEP > +EXPORT_SYMBOL_GPL(namespace_sem); > +#endif > static HLIST_HEAD(unmounted); /* protected by namespace_sem */ > static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */ > > diff --git a/include/linux/mount.h b/include/linux/mount.h > index 1ea326c368f7..6277435f6748 100644 > --- a/include/linux/mount.h > +++ b/include/linux/mount.h > @@ -80,6 +80,10 @@ static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt) > return smp_load_acquire(&mnt->mnt_idmap); > } > > +#ifdef CONFIG_LOCKDEP > +extern struct rw_semaphore namespace_sem; > +#endif Nope, we're not putting namespace_sem in a header. The code it protects is massively sensitive and it interacts with mount_lock and other locks. This stays private to fs/namespace.c as far as I'm concerned.
