[PATCH 3.5 12/71] NFS: Fix a delegation callback race

[Luis Henriques]

3.5.7.33 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <trond.myklebust at primarydata.com>

commit 755a48a7a4eb05b9c8424e3017d947b2961a60e0 upstream.

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 at intel.com>
Link: http://lkml.kernel.org/r/5313E9F6.2020405@intel.com
Fixes: 36281caa839f (NFSv4: Further clean-ups of delegation stateid validation)
Signed-off-by: Trond Myklebust <trond.myklebust at primarydata.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/nfs/delegation.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index bd3a960..04cae5c 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -548,16 +548,19 @@ 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 *
-- 
1.9.1