NFSv4.1: Return NFS4ERR_BADSESSION to callbacks during session resets

If the client is in the process of resetting the session when it receives
a callback, then returning NFS4ERR_DELAY may cause a deadlock with the
DESTROY_SESSION call.

Basically, if the client returns NFS4ERR_DELAY in response to the
CB_SEQUENCE call, then the server is entitled to believe that the
client is busy because it is already processing that call. In that
case, the server is perfectly entitled to respond with a
NFS4ERR_BACK_CHAN_BUSY to any DESTROY_SESSION call.

Fix this by having the client reply with a NFS4ERR_BADSESSION in
response to the callback if it is resetting the session.

Cc: stable@kernel.org [2.6.38+]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
index 0ab82020f5db2e9a3b786fe54af35625e760a2cb..43926add945b0a4a88625b23062e1cdd393a743d 100644 (file)
--- a/fs/nfs/callback_proc.c
+++ b/fs/nfs/callback_proc.c
@@ -452,6 +452,11 @@ __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
        if (test_bit(NFS4_SESSION_DRAINING, &clp->cl_session->session_state)) {
                spin_unlock(&tbl->slot_tbl_lock);
                status = htonl(NFS4ERR_DELAY);
+               /* Return NFS4ERR_BADSESSION if we're draining the session
+                * in order to reset it.
+                */
+               if (test_bit(NFS4CLNT_SESSION_RESET, &clp->cl_state))
+                       status = htonl(NFS4ERR_BADSESSION);
                goto out;
        }