nfsd: hold ->cl_lock for hash_delegation_locked()

The protocol for creating a new state in nfsd is to allocate the state
leaving it largely uninitialised, add that state to the ->cl_stateids
idr so as to reserve a state-id, then complete initialisation of the
state and only set ->sc_type to non-zero once the state is fully
initialised.

If a state is found in the idr with ->sc_type == 0, it is ignored.
The ->cl_lock lock is used to avoid races - it is held while checking
sc_type during lookup, and held when a non-zero value is stored in
->sc_type.

... except... hash_delegation_locked() finalises the initialisation of a
delegation state, but does NOT hold ->cl_lock.

So this patch takes ->cl_lock at the appropriate time w.r.t other locks,
and so ensures there are no races (which are extremely unlikely in any
case).
As ->fi_lock is often taken when ->cl_lock is held, we need to take
->cl_lock first of those two.
Currently ->cl_lock and state_lock are never both taken at the same time.
We need both for this patch so an arbitrary choice is needed concerning
which to take first.  As state_lock is more global, it might be more
contended, so take it first.

Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: NeilBrown <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

fs/nfsd/nfs4state.c

@@ -1312,6 +1312,7 @@ hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
 
  lockdep_assert_held(&state_lock);
  lockdep_assert_held(&fp->fi_lock);
+ lockdep_assert_held(&clp->cl_lock);
 
  if (nfs4_delegation_exists(clp, fp))
  return -EAGAIN;
@@ -5560,9 +5561,11 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
  goto out_unlock;
 
  spin_lock(&state_lock);
+ spin_lock(&clp->cl_lock);
  spin_lock(&fp->fi_lock);
  status = hash_delegation_locked(dp, fp);
  spin_unlock(&fp->fi_lock);
+ spin_unlock(&clp->cl_lock);
  spin_unlock(&state_lock);
 
  if (status)