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 + extern int mnt_want_write(struct vfsmount *mnt); extern int mnt_want_write_file(struct file *file); extern void mnt_drop_write(struct vfsmount *mnt); diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 55e5f0110e3b..32d693a797b9 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1440,13 +1440,12 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) lockdep_assert_held(&css_set_lock); - rcu_read_lock(); + /* namespace_sem ensures `root` stability on unmount */ + lockdep_assert(lockdep_is_held_type(&namespace_sem, -1)); cset = current->nsproxy->cgroup_ns->root_cset; res = __cset_cgroup_from_root(cset, root); - rcu_read_unlock(); - return res; } @@ -1454,7 +1453,7 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) * Look up cgroup associated with current task's cgroup namespace on the default * hierarchy. * - * Unlike current_cgns_cgroup_from_root(), this doesn't need locks: + * Relaxed locking requirements: * - Internal rcu_read_lock is unnecessary because we don't dereference any rcu * pointers. * - css_set_lock is not needed because we just read cset->dfl_cgrp. -- 2.40.1
