NFS: Fix a delegation callback race

The clean-up in commit 36281caa839f ended up removing a NULL pointer check
that is needed in order to prevent an Oops in
nfs_async_inode_return_delegation().

Reported-by: "Yan, Zheng" <zheng.z.yan@intel.com>
Link: http://lkml.kernel.org/r/5313E9F6.2020405@intel.com
Fixes: 36281caa839f (NFSv4: Further clean-ups of delegation stateid validation)
Cc: stable@vger.kernel.org # 3.4+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index ef792f29f831..5d8ccecf5f5c 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -659,16 +659,19 @@ int nfs_async_inode_return_delegation(struct inode *inode,
 
         rcu_read_lock();
         delegation = rcu_dereference(NFS_I(inode)->delegation);
+        if (delegation == NULL)
+                goto out_enoent;
 
-        if (!clp->cl_mvops->match_stateid(&delegation->stateid, stateid)) {
-                rcu_read_unlock();
-                return -ENOENT;
-        }
+        if (!clp->cl_mvops->match_stateid(&delegation->stateid, stateid))
+                goto out_enoent;
         nfs_mark_return_delegation(server, delegation);
         rcu_read_unlock();
 
         nfs_delegation_run_state_manager(clp);
         return 0;
+out_enoent:
+        rcu_read_unlock();
+        return -ENOENT;
 }
 
 static struct inode *