Re: [PATCH v13 27/28] ovl: Verify a data dentry has been found for metacopy inode

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Mar 30, 2018 at 01:53:24PM +0300, Amir Goldstein wrote:
> On Thu, Mar 29, 2018 at 10:38 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > If we find a upper metacopy inode, make sure we also found associated data
> > dentry in lower. Otherwise copy up operation later will fail.
> >
> > There are two cases where this can happen. First case is that somehow
> > data file was removed from lower layer. Other case is that REDIRECT
> > xattr was removed due to copy up of file on another cpu (when inode is
> > shared between two dentries) and hence ovl_lookup() could not find the
> > correct dentry.
> >
> 
> Remind me again why we remove REDIRECT xattr?
> Is it a must for functionality or just for being boy scouts?
> I would prefer to avoid having to deal with races of this sort.
> You can cleanup REDIRECT for non-dir that is not metacopy
> on lookup when finding a I_NEW inode.

Ok, thinking more about it. If we were to clean REDIRECT on lookup when
finding I_NEW inode, that means we will have to always do
vfs_removexattr(OVL_XATTR_REDIRECT) on all non-metacopy non-dir files.
That does not sound like a very good idea. Its unnecessary overhead in
lookup path.

IOW, I think removing REDIRECT and doing appropriate locking around
ovl_inode->redirect is probably better.

Thanks
Vivek