NFSv4: Ensure that we don't drop a state owner more than once

Retest the RB_EMPTY_NODE() condition under the spin lock
to ensure that we don't call rb_erase() more than once on the
same state owner.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index 3b07f094f3a9..b300fb840b21 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -435,13 +435,17 @@ nfs4_alloc_state_owner(struct nfs_server *server,
 static void
 nfs4_drop_state_owner(struct nfs4_state_owner *sp)
 {
-        if (!RB_EMPTY_NODE(&sp->so_server_node)) {
+        struct rb_node *rb_node = &sp->so_server_node;
+
+        if (!RB_EMPTY_NODE(rb_node)) {
                 struct nfs_server *server = sp->so_server;
                 struct nfs_client *clp = server->nfs_client;
 
                 spin_lock(&clp->cl_lock);
-                rb_erase(&sp->so_server_node, &server->state_owners);
-                RB_CLEAR_NODE(&sp->so_server_node);
+                if (!RB_EMPTY_NODE(rb_node)) {
+                        rb_erase(rb_node, &server->state_owners);
+                        RB_CLEAR_NODE(rb_node);
+                }
                 spin_unlock(&clp->cl_lock);
         }
 }