Re: [Regression] 3.19-rc3 : memcg: Hang in mount memcg

[Johannes Weiner <hannes@cmpxchg.org>]

Hi,

On Thu, Jan 22, 2015 at 09:34:54AM -0500, Tejun Heo wrote:
> On Thu, Jan 22, 2015 at 08:45:50AM -0500, Johannes Weiner wrote:
> > diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> > index bb263d0caab3..9a09308c8066 100644
> > --- a/kernel/cgroup.c
> > +++ b/kernel/cgroup.c
> > @@ -1819,8 +1819,11 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
> >  			goto out_unlock;
> >  		}
> >  
> > -		if (root->flags ^ opts.flags)
> > -			pr_warn("new mount options do not match the existing superblock, will be ignored\n");
> > +		if (root->flags ^ opts.flags) {
> > +			pr_warn("new mount options do not match the existing superblock\n");
> > +			ret = -EBUSY;
> > +			goto out_unlock;
> > +		}
> 
> Do we really need the above chunk?

Inform and ignore or fail hard?  I guess we can drop this hunk and
keep with the current behavior.

> > @@ -1909,7 +1912,7 @@ static void cgroup_kill_sb(struct super_block *sb)
> >  	 *
> >  	 * And don't kill the default root.
> >  	 */
> > -	if (css_has_online_children(&root->cgrp.self) ||
> > +	if (!list_empty(&root->cgrp.self.children) ||
> >  	    root == &cgrp_dfl_root)
> >  		cgroup_put(&root->cgrp);
> 
> I tried to do something a bit more advanced so that eventual async
> release of dying children, if they happen, can also release the
> hierarchy but I don't think it really matters unless we can forcefully
> drain.  So, shouldn't just the above part be enough?

Yep, I'd be fine with that.

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