On 2014/2/12 10:15, Li Zefan wrote: > On 2014/2/12 0:26, Michal Hocko wrote: >> On Tue 11-02-14 10:41:05, Tejun Heo wrote: >> [...] >>> @@ -4254,12 +4256,12 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, >>> >>> return 0; >>> >>> -err_unlock: >>> - mutex_unlock(&cgroup_mutex); >>> - /* Release the reference count that we took on the superblock */ >>> - deactivate_super(sb); >>> err_free_id: >>> idr_remove(&root->cgroup_idr, cgrp->id); >>> + /* Release the reference count that we took on the superblock */ >>> + deactivate_super(sb); >>> +err_unlock: >>> + mutex_unlock(&cgroup_mutex); >>> err_free_name: >>> kfree(rcu_dereference_raw(cgrp->name)); >>> err_free_cgrp: >> >> Do I have to change deactivate_super vs. mutex_unlock ordering in my >> backport for 3.12 as well? >> > > Your change is wrong that you shouldn't drop sb refcnt in err_unlock path. > > But you made me think if it's OK to hold cgroup_mutex while calling deactivate_super(), > and the answer is NO! deactive_super() may call cgroup_kill_sb() which will > acquire cgroup_mutex. > > I'll update the patch. > > Thank Tejun we won't be entangled with vfs internal anymore after coverting > to kernfs. > On second thought, it should be safe to call deactivate_super() before releasing cgroup_mutex, as cgroup_create() is called through vfs, so vfs should guanrantee the superblock won't disapear, so this deactivate_super() won't drop sb refcnt to 0. Still this is just my guess without diving into vfs code, and we'd better not depend on it even my guess is correct. -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
