[PATCH 4.9 158/164] NFSv4: Fix a hang in OPEN related to server reboot

[Greg Kroah-Hartman]

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

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

From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

commit 56e0d71ef12f026d96213e45a662bde6bbff4676 upstream.

If the server fails to return the attributes as part of an OPEN
reply, and then reboots, we can end up hanging. The reason is that
the client attempts to send a GETATTR in order to pick up the
missing OPEN call, but fails to release the slot first, causing
reboot recovery to deadlock.

Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Fixes: 2e80dbe7ac51a ("NFSv4.1: Close callback races for OPEN, LAYOUTGET...")
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/nfs/nfs4proc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -2385,8 +2385,10 @@ static int _nfs4_proc_open(struct nfs4_o
 		if (status != 0)
 			return status;
 	}
-	if (!(o_res->f_attr->valid & NFS_ATTR_FATTR))
+	if (!(o_res->f_attr->valid & NFS_ATTR_FATTR)) {
+		nfs4_sequence_free_slot(&o_res->seq_res);
 		nfs4_proc_getattr(server, &o_res->fh, o_res->f_attr, o_res->f_label);
+	}
 	return 0;
 }