nfsd: ensure that delegation stateid hash references are only put once

It's possible that a DELEGRETURN could race with (e.g.) client expiry,
in which case we could end up putting the delegation hash reference more
than once.

Have unhash_delegation_locked return a bool that indicates whether it
was already unhashed. In the case of destroy_delegation we only
conditionally put the hash reference if that returns true.

The other callers of unhash_delegation_locked call it while walking
list_heads that shouldn't yet be detached. If we find that it doesn't
return true in those cases, then throw a WARN_ON as that indicates that
we have a partially hashed delegation, and that something is likely very
wrong.

Tested-by: Andrew W Elble <aweits@rit.edu>
Tested-by: Anna Schumaker <Anna.Schumaker@netapp.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 17 insertions, 9 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f318e706cb35..416f32e34a33 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -777,13 +777,16 @@ hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
         list_add(&dp->dl_perclnt, &dp->dl_stid.sc_client->cl_delegations);
 }
 
-static void
+static bool
 unhash_delegation_locked(struct nfs4_delegation *dp)
 {
         struct nfs4_file *fp = dp->dl_stid.sc_file;
 
         lockdep_assert_held(&state_lock);
 
+        if (list_empty(&dp->dl_perfile))
+                return false;
+
         dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
         /* Ensure that deleg break won't try to requeue it */
         ++dp->dl_time;
@@ -792,16 +795,21 @@ unhash_delegation_locked(struct nfs4_delegation *dp)
         list_del_init(&dp->dl_recall_lru);
         list_del_init(&dp->dl_perfile);
         spin_unlock(&fp->fi_lock);
+        return true;
 }
 
 static void destroy_delegation(struct nfs4_delegation *dp)
 {
+        bool unhashed;
+
         spin_lock(&state_lock);
-        unhash_delegation_locked(dp);
+        unhashed = unhash_delegation_locked(dp);
         spin_unlock(&state_lock);
-        put_clnt_odstate(dp->dl_clnt_odstate);
-        nfs4_put_deleg_lease(dp->dl_stid.sc_file);
-        nfs4_put_stid(&dp->dl_stid);
+        if (unhashed) {
+                put_clnt_odstate(dp->dl_clnt_odstate);
+                nfs4_put_deleg_lease(dp->dl_stid.sc_file);
+                nfs4_put_stid(&dp->dl_stid);
+        }
 }
 
 static void revoke_delegation(struct nfs4_delegation *dp)
@@ -1730,7 +1738,7 @@ __destroy_client(struct nfs4_client *clp)
         spin_lock(&state_lock);
         while (!list_empty(&clp->cl_delegations)) {
                 dp = list_entry(clp->cl_delegations.next, struct nfs4_delegation, dl_perclnt);
-                unhash_delegation_locked(dp);
+                WARN_ON(!unhash_delegation_locked(dp));
                 list_add(&dp->dl_recall_lru, &reaplist);
         }
         spin_unlock(&state_lock);
@@ -4357,7 +4365,7 @@ nfs4_laundromat(struct nfsd_net *nn)
                         new_timeo = min(new_timeo, t);
                         break;
                 }
-                unhash_delegation_locked(dp);
+                WARN_ON(!unhash_delegation_locked(dp));
                 list_add(&dp->dl_recall_lru, &reaplist);
         }
         spin_unlock(&state_lock);
@@ -6314,7 +6322,7 @@ static u64 nfsd_find_all_delegations(struct nfs4_client *clp, u64 max,
                                 continue;
 
                         atomic_inc(&clp->cl_refcount);
-                        unhash_delegation_locked(dp);
+                        WARN_ON(!unhash_delegation_locked(dp));
                         list_add(&dp->dl_recall_lru, victims);
                 }
                 ++count;
@@ -6645,7 +6653,7 @@ nfs4_state_shutdown_net(struct net *net)
         spin_lock(&state_lock);
         list_for_each_safe(pos, next, &nn->del_recall_lru) {
                 dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
-                unhash_delegation_locked(dp);
+                WARN_ON(!unhash_delegation_locked(dp));
                 list_add(&dp->dl_recall_lru, &reaplist);
         }
         spin_unlock(&state_lock);