On Sat, Jan 12, 2019 at 05:38:25AM +0000, Al Viro wrote: > On Fri, Jan 11, 2019 at 12:54:51PM -0800, Tejun Heo wrote: > > Hello, Al. > > > > On Fri, Jan 11, 2019 at 07:23:09AM +0000, Al Viro wrote: > > > AFAICS, a cleaner solution would be this: > > > * to hell with kernfs_pin_sb(); just try to grab a reference to > > > cgroup_root on reuse. > > > * have cgroup_kill_sb() treat "it's already marked killed" as > > > "just drop the reference, then". > > > * after cgroup_do_mount() check if cgroup_root got marked killed and > > > do deactivate_locked_super() in such case (with the same > > > restart_syscall() failure exit). > > > > > > Objections? I would love to kill kernfs_pin_sb() as > > > a followup (it's a fundamentally broken API), but that's not > > > a stable fodder; some fix of refcounting bugs, OTOH, should be. > > > > cgroup1 hierarchies have really weird set of requirements and the > > implementation has always been somewhat broken. I thought I fixed it > > but obviously not. I have no objection whatsoever and would much > > appreciate the work. > > See vfs.git #fixes (the last two commits in there). It seems to > work here, but I don't have the CRIU regression tests, etc., so > I would really appreciate if that thing got a real beating. BTW, while kernfs_pin_sb() and struct kernfs_root ->supers definitely ought to die, there's something else that might be killable with that approach. percpu_ref_reinit() has no users left after that, and, as David Howells has observed, PERCPU_REF_INIT_DEAD is also unused. Do we want to keep these two?
