linux-kernel - Re: [PATCH 7/8] cgroup: mount cgroupns-root when inside non-init cgroupns

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Date:	Mon, 7 Dec 2015 15:53:01 +0000
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	serge@...lyn.com, linux-kernel@...r.kernel.org,
	adityakali@...gle.com, linux-api@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	lxc-devel@...ts.linuxcontainers.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com
Subject: Re: [PATCH 7/8] cgroup: mount cgroupns-root when inside non-init
 cgroupns

Quoting Tejun Heo (tj@...nel.org):
> Hello, Serge.
> 
> On Thu, Dec 03, 2015 at 04:47:06PM -0600, Serge E. Hallyn wrote:
> ...
> > +	dentry = dget(sb->s_root);
> > +	if (!kn->parent) // this is the root
> > +		return dentry;
> > +
> > +	knparent = find_kn_ancestor_below(kn, NULL);
> > +	BUG_ON(!knparent);
> 
> Doing WARN_ON() and returning failure is better, I think.  Failing ns
> mount is an okay failure mode and a lot better than crashing the
> system.

Ok - this shouldn't be user-triggerable, so if it happens it really
is a bug in our code, but I'll change it,

> Also, how about find_next_ancestor() for the name of the
> function?

Yeah it's static anyway :)

will change, squash, and resend the set.

> > +	do {
> > +		struct dentry *dtmp;
> > +		struct kernfs_node *kntmp;
> > +
> > +		if (kn == knparent)
> > +			return dentry;
> > +		kntmp = find_kn_ancestor_below(kn, knparent);
> > +		BUG_ON(!kntmp);
> > +		dtmp = lookup_one_len(kntmp->name, dentry, strlen(kntmp->name));
> > +		dput(dentry);
> > +		if (IS_ERR(dtmp))
> > +			return dtmp;
> > +		knparent = kntmp;
> > +		dentry = dtmp;
> > +	} while (1);
> 
> Other than the nitpicks, looks good to me.
> 
> Thanks.
> 
> -- 
> tejun
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