linux-kernel - [PATCH 4.16 048/196] cifs: smbd: avoid reconnect lockup

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Message-Id: <20180422135106.570822475@linuxfoundation.org>
Date:   Sun, 22 Apr 2018 15:51:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Long Li <longli@...rosoft.com>,
        Steve French <smfrench@...il.com>,
        Ronnie Sahlberg <lsahlber@...hat.com>
Subject: [PATCH 4.16 048/196] cifs: smbd: avoid reconnect lockup

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

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

From: Long Li <longli@...rosoft.com>

commit 48f238a79f668f8ff013024d83010de551833d7f upstream.

During transport reconnect, other processes may have registered memory
and blocked on transport. This creates a deadlock situation because the
transport resources can't be freed, and reconnect is blocked.

Fix this by returning to upper layer on timeout. Before returning,
transport status is set to reconnecting so other processes will release
memory registration resources.

Upper layer will retry the reconnect. This is not in fast I/O path so
setting the timeout to 5 seconds.

Signed-off-by: Long Li <longli@...rosoft.com>
Signed-off-by: Steve French <smfrench@...il.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@...hat.com>
CC: Stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/cifs/smbdirect.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/fs/cifs/smbdirect.c
+++ b/fs/cifs/smbdirect.c
@@ -1498,8 +1498,8 @@ int smbd_reconnect(struct TCP_Server_Inf
 	log_rdma_event(INFO, "reconnecting rdma session\n");
 
 	if (!server->smbd_conn) {
-		log_rdma_event(ERR, "rdma session already destroyed\n");
-		return -EINVAL;
+		log_rdma_event(INFO, "rdma session already destroyed\n");
+		goto create_conn;
 	}
 
 	/*
@@ -1512,15 +1512,19 @@ int smbd_reconnect(struct TCP_Server_Inf
 	}
 
 	/* wait until the transport is destroyed */
-	wait_event(server->smbd_conn->wait_destroy,
-		server->smbd_conn->transport_status == SMBD_DESTROYED);
+	if (!wait_event_timeout(server->smbd_conn->wait_destroy,
+		server->smbd_conn->transport_status == SMBD_DESTROYED, 5*HZ))
+		return -EAGAIN;
 
 	destroy_workqueue(server->smbd_conn->workqueue);
 	kfree(server->smbd_conn);
 
+create_conn:
 	log_rdma_event(INFO, "creating rdma session\n");
 	server->smbd_conn = smbd_get_connection(
 		server, (struct sockaddr *) &server->dstaddr);
+	log_rdma_event(INFO, "created rdma session info=%p\n",
+		server->smbd_conn);
 
 	return server->smbd_conn ? 0 : -ENOENT;
 }