linux-kernel - Re: [PATCH 04/11] vfs: check unlinked ancestors before mount

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Date:	Thu, 5 Sep 2013 17:07:29 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>,
	David Howells <dhowells@...hat.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 04/11] vfs: check unlinked ancestors before mount

On Thu, Sep 05, 2013 at 05:52:51PM +0200, Miklos Szeredi wrote:
> On Thu, Sep 5, 2013 at 4:56 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > I'd probably just do this, and to hell with helper functions...
> >
> > int d_set_mounted(struct dentry *dentry)
> > {
> >         struct dentry *p;
> >         int ret = 0;
> >         write_seqlock(&rename_lock);
> >         for (p = dentry; !IS_ROOT(p); p = p->d_parent) {
> >                 /* Need exclusion wrt. check_submounts_and_drop() */
> >                 spin_lock(&p->d_lock);
> >                 if (unlikely(d_unhashed(p))) {
> >                         spin_unlock(&p->d_lock);
> >                         ret = -ENOENT;
> >                         goto out;
> >                 }
> >                 spin_unlock(&p->d_lock);
> >         }
> >         spin_lock(&dentry->d_lock);
> >         dentry->d_flags |= DCACHE_MOUNTED;
> >         spin_unlock(&dentry->d_lock);
> > out:
> >         write_sequnlock(&rename_lock);
> >         return ret;
> > }
> 
> One issue with that: the dentry should be checked and marked within
> the same d_locked region.   Because e.g. d_invalidate() relies solely
> on d_lock for non-dir mounts and d_mountpoint() checking, no
> rename_lock protection there.

Point...  OK, could you check if vfs.git#for-miklos looks sane now?  It should
be at cf7543f...
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