On Tue, 2020-01-28 at 15:21 -0500, Trond Myklebust wrote:
> On Tue, 2020-01-28 at 10:56 -0500, Trond Myklebust wrote:
> > On Tue, 2020-01-28 at 10:26 -0500, Benjamin Coddington wrote:
> > > If we skip lookup revalidataion while holding a delegation, we
> > > might
> > > miss
> > > that the file has changed directories on the server. This can
> > > happen
> > > if
> > > the file is moved in between the client caching a dentry and
> > > obtaining a
> > > delegation. That can be reproduced on a single system with this
> > > bash:
> > >
> > > mkdir -p /exports/dir{1,2}
> > > exportfs -o rw localhost:/exports
> > > mount -t nfs -ov4.1,noac localhost:/exports /mnt/localhost
> > >
> > > touch /exports/dir1/fubar
> > >
> > > cat /mnt/localhost/dir1/fubar
> > > mv /mnt/localhost/dir{1,2}/fubar
> > >
> > > mv /exports/dir{2,1}/fubar
> > >
> > > cat /mnt/localhost/dir1/fubar
> > > mv /mnt/localhost/dir{1,2}/fubar
> > >
> > > In this example, the final `mv` will stat source and destination
> > > and
> > > find
> > > they are the same dentry.
> > >
> > > To fix this without giving up the increased lookup performance
> > > that
> > > holding
> > > a delegation provides, let's revalidate the dentry only once
> > > after
> > > obtaining a delegation by placing a magic value in the dentry's
> > > verifier.
> > >
> > > Suggested-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> > > ---
> > > fs/nfs/dir.c | 22 ++++++++++++++++++++--
> > > 1 file changed, 20 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > > index e180033e35cf..e9d07dcd6d6f 100644
> > > --- a/fs/nfs/dir.c
> > > +++ b/fs/nfs/dir.c
> > > @@ -949,6 +949,7 @@ static int nfs_fsync_dir(struct file *filp,
> > > loff_t start, loff_t end,
> > > return 0;
> > > }
> > >
> > > +#define NFS_DELEGATION_VERF 0xfeeddeaf
> > > /**
> > > * nfs_force_lookup_revalidate - Mark the directory as having
> > > changed
> > > * @dir: pointer to directory inode
> > > @@ -962,6 +963,8 @@ static int nfs_fsync_dir(struct file *filp,
> > > loff_t start, loff_t end,
> > > void nfs_force_lookup_revalidate(struct inode *dir)
> > > {
> > > NFS_I(dir)->cache_change_attribute++;
> > > + if (NFS_I(dir)->cache_change_attribute == NFS_DELEGATION_VERF)
> > > + NFS_I(dir)->cache_change_attribute++;
> >
> > Actually, I think a slight modification to this can might be
> > beneficial. If we change to the following:
> >
> > if (unlikely(NFS_I(dir)->cache_change_attribute ==
> > NFS_DELEGATION_VERF - 1))
> > NFS_I(dir)->cache_change_attribute =
> > NFS_DELEGATION_VERF + 1;
> > else
> > NFS_I(dir)->cache_change_attribute++;
> >
>
> ...actually, it would be nice to clean that up too using a
> declaration
> of 'struct nfs_inode *nfsi = NFS_I(dir));'
>
> > then that should ensure those readers of cache_change_attribute
> > that
> > do
> > not use locking will also never see the value NFS_DELEGATION_VERF
> > (assuming that gcc doesn't optimise the above to something weird).
> >
> > > }
> > > EXPORT_SYMBOL_GPL(nfs_force_lookup_revalidate);
> > >
> > > @@ -1133,6 +1136,7 @@ nfs_lookup_revalidate_dentry(struct inode
> > > *dir,
> > > struct dentry *dentry,
> > > struct nfs_fh *fhandle;
> > > struct nfs_fattr *fattr;
> > > struct nfs4_label *label;
> > > + unsigned long verifier;
> > > int ret;
> > >
> > > ret = -ENOMEM;
> > > @@ -1154,6 +1158,11 @@ nfs_lookup_revalidate_dentry(struct inode
> > > *dir, struct dentry *dentry,
> > > if (nfs_refresh_inode(inode, fattr) < 0)
> > > goto out;
> > >
> > > + if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> > > + verifier = NFS_DELEGATION_VERF;
> > > + else
> > > + verifier = nfs_save_change_attribute(dir);
> > > +
> > > nfs_setsecurity(inode, fattr, label);
> > > nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
>
> Oops! When reviewing, I missed this. Shouldn't the above be changed
> to
> nfs_set_verifier(dentry, verifier) ?
...and on a similar vein: nfs_lookup_revalidate_delegated() needs to
change so as to not reset the verifier...
Sorry for not catching that one either.
>
> > >
> > > @@ -1167,6 +1176,15 @@ nfs_lookup_revalidate_dentry(struct inode
> > > *dir, struct dentry *dentry,
> > > return nfs_lookup_revalidate_done(dir, dentry, inode, ret);
> > > }
> > >
> > > +static int nfs_delegation_matches_dentry(struct inode *dir,
> > > + struct dentry *dentry, struct inode *inode)
> > > +{
> > > + if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ) &&
> > > + dentry->d_time == NFS_DELEGATION_VERF)
> > > + return 1;
> > > + return 0;
> > > +}
> > > +
> > > /*
> > > * This is called every time the dcache has a lookup hit,
> > > * and we should check whether we can really trust that
> > > @@ -1197,7 +1215,7 @@ nfs_do_lookup_revalidate(struct inode *dir,
> > > struct dentry *dentry,
> > > goto out_bad;
> > > }
> > >
> > > - if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> > > + if (nfs_delegation_matches_dentry(dir, dentry, inode))
> > > return nfs_lookup_revalidate_delegated(dir, dentry,
> > > inode);
> > >
> > > /* Force a full look up iff the parent directory has changed */
> > > @@ -1635,7 +1653,7 @@ 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))
> > > + if (nfs_delegation_matches_dentry(dir, dentry, inode))
> > > return nfs_lookup_revalidate_delegated(dir, dentry,
> > > inode);
> > >
> > > /* NFS only supports OPEN on regular files */
--
Trond Myklebust
CTO, Hammerspace Inc
4300 El Camino Real, Suite 105
Los Altos, CA 94022
www.hammer.space
