NFSv4: Fix the locking in nfs_inode_reclaim_delegation()

Ensure that we correctly rcu-dereference the delegation itself, and that we
protect against removal while we're changing the contents.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 28 insertions, 14 deletions

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 15671245c6ee..8d9ec494a944 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -129,21 +129,35 @@ again:
  */
 void nfs_inode_reclaim_delegation(struct inode *inode, struct rpc_cred *cred, struct nfs_openres *res)
 {
-        struct nfs_delegation *delegation = NFS_I(inode)->delegation;
-        struct rpc_cred *oldcred;
+        struct nfs_delegation *delegation;
+        struct rpc_cred *oldcred = NULL;
 
-        if (delegation == NULL)
-                return;
-        memcpy(delegation->stateid.data, res->delegation.data,
-                        sizeof(delegation->stateid.data));
-        delegation->type = res->delegation_type;
-        delegation->maxsize = res->maxsize;
-        oldcred = delegation->cred;
-        delegation->cred = get_rpccred(cred);
-        clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
-        NFS_I(inode)->delegation_state = delegation->type;
-        smp_wmb();
-        put_rpccred(oldcred);
+        rcu_read_lock();
+        delegation = rcu_dereference(NFS_I(inode)->delegation);
+        if (delegation != NULL) {
+                spin_lock(&delegation->lock);
+                if (delegation->inode != NULL) {
+                        memcpy(delegation->stateid.data, res->delegation.data,
+                               sizeof(delegation->stateid.data));
+                        delegation->type = res->delegation_type;
+                        delegation->maxsize = res->maxsize;
+                        oldcred = delegation->cred;
+                        delegation->cred = get_rpccred(cred);
+                        clear_bit(NFS_DELEGATION_NEED_RECLAIM,
+                                  &delegation->flags);
+                        NFS_I(inode)->delegation_state = delegation->type;
+                        spin_unlock(&delegation->lock);
+                        put_rpccred(oldcred);
+                        rcu_read_unlock();
+                } else {
+                        /* We appear to have raced with a delegation return. */
+                        spin_unlock(&delegation->lock);
+                        rcu_read_unlock();
+                        nfs_inode_set_delegation(inode, cred, res);
+                }
+        } else {
+                rcu_read_unlock();
+        }
 }
 
 static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)