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>

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index ef792f2..5d8ccec 100644 (file)
--- 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 *