Re: [heads-up] buggered refcounting logics in cgroup1_mount()

[Zefan Li <lizefan@huawei.com>]

On 2019/1/12 4:54, 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.
> 
> Thanks a lot and happy new year!
> 

+1.

We've fixed bugs there quite a few times. Would be great to see it's fixed
once and for all. Thnaks for the work!