Patch "nfsd: back channel stuck in SEQ4_STATUS_CB_PATH_DOWN" has been added to the 5.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nfsd: back channel stuck in SEQ4_STATUS_CB_PATH_DOWN

to the 5.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-back-channel-stuck-in-seq4_status_cb_path_down.patch
and it can be found in the queue-5.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5b8d14945fbe1c2253721b9b5dbf4d36fa83f644
Author: Dai Ngo <dai.ngo@xxxxxxxxxx>
Date:   Thu Sep 16 14:22:12 2021 -0400

    nfsd: back channel stuck in SEQ4_STATUS_CB_PATH_DOWN
    
    [ Upstream commit 02579b2ff8b0becfb51d85a975908ac4ab15fba8 ]
    
    When the back channel enters SEQ4_STATUS_CB_PATH_DOWN state, the client
    recovers by sending BIND_CONN_TO_SESSION but the server fails to recover
    the back channel and leaves it as NFSD4_CB_DOWN.
    
    Fix by enhancing nfsd4_bind_conn_to_session to probe the back channel
    by calling nfsd4_probe_callback.
    
    Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 3d805f5b1f5d..1c33a5255893 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -3570,7 +3570,7 @@ static struct nfsd4_conn *__nfsd4_find_conn(struct svc_xprt *xpt, struct nfsd4_s
 }
 
 static __be32 nfsd4_match_existing_connection(struct svc_rqst *rqst,
-				struct nfsd4_session *session, u32 req)
+		struct nfsd4_session *session, u32 req, struct nfsd4_conn **conn)
 {
 	struct nfs4_client *clp = session->se_client;
 	struct svc_xprt *xpt = rqst->rq_xprt;
@@ -3593,6 +3593,8 @@ static __be32 nfsd4_match_existing_connection(struct svc_rqst *rqst,
 	else
 		status = nfserr_inval;
 	spin_unlock(&clp->cl_lock);
+	if (status == nfs_ok && conn)
+		*conn = c;
 	return status;
 }
 
@@ -3617,8 +3619,16 @@ __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
 	status = nfserr_wrong_cred;
 	if (!nfsd4_mach_creds_match(session->se_client, rqstp))
 		goto out;
-	status = nfsd4_match_existing_connection(rqstp, session, bcts->dir);
-	if (status == nfs_ok || status == nfserr_inval)
+	status = nfsd4_match_existing_connection(rqstp, session,
+			bcts->dir, &conn);
+	if (status == nfs_ok) {
+		if (bcts->dir == NFS4_CDFC4_FORE_OR_BOTH ||
+				bcts->dir == NFS4_CDFC4_BACK)
+			conn->cn_flags |= NFS4_CDFC4_BACK;
+		nfsd4_probe_callback(session->se_client);
+		goto out;
+	}
+	if (status == nfserr_inval)
 		goto out;
 	status = nfsd4_map_bcts_dir(&bcts->dir);
 	if (status)