NFSv4: Fix a hang in OPEN related to server reboot

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@primarydata.com>
Fixes: 2e80dbe7ac51a ("NFSv4.1: Close callback races for OPEN, LAYOUTGET...")
Cc: stable@vger.kernel.org # v4.8+

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 4e52ac773d1f531d2b2128db3a554968c5f1a6d6..6e9ff2d9a5bf5cf7db104e1e952a12c3e823834d 100644 (file)
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -2300,8 +2300,10 @@ static int _nfs4_proc_open(struct nfs4_opendata *data)
                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;
 }