On Tue, Apr 10, 2018 at 10:29:00PM +0300, Amir Goldstein wrote:
> On Tue, Apr 10, 2018 at 10:20 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > On Tue, Apr 10, 2018 at 5:00 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> [...]
> >>
> >> In fact I see OVL_INDEX being used in ovl_getattr(). If a parallel copy
> >> up took place it is possible that ovl_getattr() saw upperdentry but not
> >> the OVL_INDEX. And then nlink count will be off. IOW, what barrier/lock
> >> guarantees that this does not happen.
> >>
> >
> > Yes. and that is not the only problem I see with ovl_getattr().
> >
> > stat->dev could be set to ovl_get_pseudo_dev(dentry), even
> > if stat->ino is not set to lowerstat.ino; that is not good.
> >
> > If I am not mistaken, all the special conditions in ovl_getattr()
> > to use lower st_ino are already encoded in ovl_hash_bylower(),
> > so you may completely remove those extra tests if
> > OVL_TYPE_ORIGIN(type) already checks the OVL_BYLOWER
> > flag.
> >
> > It may be hard to see my claim above is true, because, for
> > example, sb->s_export_op in ovl_hash_bylower() is equivalent
> > to ovl_verify_lower(dentry->d_sb) in ovl_getattr().
> >
> > Please double check my claims, and if you agree, you can submit a
> > patch that Fixes: ("a0c5ad307ac0 ovl: relax same fs constraint for
> > constant st_ino"), which already does the right thing for metacopy.
> >
>
> On second thought, it would be better to submit the simple fix patch
> first, so it could be applied to stable kernels that don't have
> ovl_hash_bylower() and only then submit the patch that adds
> OVL_BYLOWER and removes the extra tests in ovl_getattr().
> Something like this (untested) should do.
> Let me know if you would like me to submit the fix patch.
Frankly speaking I don't understand the fix. So I would prefer that
you submit it with a proper commit message.
Vivek
>
> Thanks,
> Amir.
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 3b1bd469accd..34fe86dedd3b 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -118,13 +118,10 @@ int ovl_getattr(const struct path *path, struct
> kstat *stat,
> */
> if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
> (!ovl_verify_lower(dentry->d_sb) &&
> - (is_dir || lowerstat.nlink == 1)))
> + (is_dir || lowerstat.nlink == 1))) {
> stat->ino = lowerstat.ino;
> -
> - if (samefs)
> - WARN_ON_ONCE(stat->dev != lowerstat.dev);
> - else
> stat->dev = ovl_get_pseudo_dev(dentry);
> + }
> }
> if (samefs) {
> /*
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