On Tue, 22 Mar 2011, Al Viro wrote:
> On Tue, Mar 22, 2011 at 09:06:38PM +0100, Miklos Szeredi wrote:
> > On Tue, 22 Mar 2011, Al Viro wrote:
> > > Proceeding with rename is not interesting; proceeding with copyup is.
> > >
> > > Who said that by the time we get to copy_up_locked you will still have
> > > dentry (and upper) match lowerpath? Or that ->d_parent on overlay and
> > > on upper will change in sync, for that matter - there are two d_move()
> > > calls involved...
> >
> > If rename is involved, than rename itself already did the copy up.
> > And that's checked before proceeding with the actual copy up. If
> > there was no rename, then that guarantees that things are in sync, at
> > least for the duration of the copy up.
>
> What do you mean, before? It's not atomic... What happens if e.g.
> you get
>
> A: decided to do copy_up_locked
> blocked on i_mutex
>
> B: did copy_up
> did rename(), complete with d_move()
> did unlink() in new place
>
> A: got CPU back, got i_mutex
Here it can check if the file was copied up or not. OK, I see the
code doesn't quite get that right.
Patch below would fix it, I think.
Thanks,
Miklos
diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
index e7fcbde..0a1137b 100644
--- a/fs/overlayfs/overlayfs.c
+++ b/fs/overlayfs/overlayfs.c
@@ -1269,8 +1269,7 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
* racing with rename (rename means the copy up was already
* successful).
*/
- if (dentry->d_parent != parent) {
- WARN_ON((ovl_path_type(dentry) == OVL_PATH_LOWER));
+ if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
err = 0;
} else {
err = ovl_copy_up_locked(upperdir, dentry, lowerpath,
--
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