On Thu, 2020-01-16 at 10:19 -0500, Benjamin Coddington wrote:
> I'd like to bump this one again while we're talking about
> lookup/revalidation.
>
> We have folks that hit this problem in the field:
> - client caches a dentry
> - file gets moved
> - server gives out a delegation
> - client never notices the change because we always skip
> revalidation
>
> Is this the wrong place to fix this? Any other feedback?
>
> Ben
>
> On 19 Sep 2019, at 10:49, Benjamin Coddington wrote:
>
> > If we skip lookup revalidation while holding a delegation, we
> > might
> > miss
> > that the file has changed directories on the server. The
> > directory's
> > change attribute should still be checked against the dentry's
> > d_time
> > to
> > perform a complete revalidation.
> >
> > V2 - Add some commentary as suggested-by J. Bruce Fields.
> >
> > Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> > ---
> > fs/nfs/dir.c | 17 +++++++++++------
> > 1 file changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > index 0adfd8840110..8723e82f5c9d 100644
> > --- a/fs/nfs/dir.c
> > +++ b/fs/nfs/dir.c
> > @@ -1197,12 +1197,20 @@ nfs_do_lookup_revalidate(struct inode
> > *dir,
> > struct dentry *dentry,
> > goto out_bad;
> > }
> >
> > - if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> > - return nfs_lookup_revalidate_delegated(dir, dentry,
> > inode);
> > -
> > /* Force a full look up iff the parent directory has changed */
> > if (!(flags & (LOOKUP_EXCL | LOOKUP_REVAL)) &&
> > nfs_check_verifier(dir, dentry, flags & LOOKUP_RCU)) {
> > +
> > + /*
> > + * Note that the file can't move while we hold a
> > + * delegation. But this dentry could have been cached
> > + * before we got a delegation. So it's only safe to
> > + * skip revalidation when the parent directory is
> > + * unchanged:
> > + */
> > + if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> > + return nfs_lookup_revalidate_delegated(dir,
> > dentry, inode);
> > +
> > error = nfs_lookup_verify_inode(inode, flags);
> > if (error) {
> > if (error == -ESTALE)
> > @@ -1635,9 +1643,6 @@ nfs4_do_lookup_revalidate(struct inode *dir,
> > struct dentry *dentry,
> > if (inode == NULL)
> > goto full_reval;
> >
> > - if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> > - return nfs_lookup_revalidate_delegated(dir, dentry,
> > inode);
> > -
> > /* NFS only supports OPEN on regular files */
> > if (!S_ISREG(inode->i_mode))
> > goto full_reval;
> > --
> > 2.20.1
We should need to perform this revalidation once, and only once for
that directory, and only if we opened the file using a CLAIM_FH open,
or if we opened it through a different hard linked name (and did not
create this hard link after we got the delegation).
Perhaps we could define a magic value for dentry->d_time that causes us
to skip revalidation if and only if we hold a delegation?
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
