Hey,
On Wed, Jun 25, 2014 at 09:56:31AM +0800, Li Zefan wrote:
> > Hmmm? Why does that matter? The only region in cgroup_mount() which
> > needs to be put inside such mutex would be root lookup, no?
>
> unfortunately that won't help. I think what you suggest is:
>
> cgroup_mount()
> {
> mutex_lock();
> lookup_cgroup_root();
> mutex_unlock();
> kernfs_mount();
> }
>
> cgroup_kill_sb()
> {
> mutex_lock();
> percpu_ref_kill();
> mutex_Unlock();
> kernfs_kill_sb();
> }
>
> See, we may still be destroying the superblock after we've succeeded
> in getting the refcnt of cgroup root.
Sure, but now the decision to kill is synchronized so the other side
can interlock with it. e.g.
cgroup_mount()
{
mutex_lock();
lookup_cgroup_root();
if (root isn't killed yet)
root->this_better_stay_alive++;
mutex_unlock();
kernfs_mount();
}
cgroup_kill_sb()
{
mutex_lock();
if (check whether root can be killed)
percpu_ref_kill();
mutex_unlock();
if (the above condition was true)
kernfs_kill_sb();
}
--
tejun
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