Patch "rxrpc: Make rxrpc_kernel_get_srtt() indicate validity" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    rxrpc: Make rxrpc_kernel_get_srtt() indicate validity

to the 5.4-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:
     rxrpc-make-rxrpc_kernel_get_srtt-indicate-validity.patch
and it can be found in the queue-5.4 subdirectory.

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



commit 0b647ba3c11fbf8f44fcb34b7e4a11e0d7d16660
Author: David Howells <dhowells@xxxxxxxxxx>
Date:   Thu Aug 20 15:13:00 2020 +0100

    rxrpc: Make rxrpc_kernel_get_srtt() indicate validity
    
    [ Upstream commit 1d4adfaf65746203861c72d9d78de349eb97d528 ]
    
    Fix rxrpc_kernel_get_srtt() to indicate the validity of the returned
    smoothed RTT.  If we haven't had any valid samples yet, the SRTT isn't
    useful.
    
    Fixes: c410bf01933e ("rxrpc: Fix the excessive initial retransmission timeout")
    Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/afs/fs_probe.c b/fs/afs/fs_probe.c
index 02e976ca5732f..51ee3dd79700f 100644
--- a/fs/afs/fs_probe.c
+++ b/fs/afs/fs_probe.c
@@ -92,8 +92,8 @@ responded:
 		}
 	}
 
-	rtt_us = rxrpc_kernel_get_srtt(call->net->socket, call->rxcall);
-	if (rtt_us < server->probe.rtt) {
+	if (rxrpc_kernel_get_srtt(call->net->socket, call->rxcall, &rtt_us) &&
+	    rtt_us < server->probe.rtt) {
 		server->probe.rtt = rtt_us;
 		alist->preferred = index;
 		have_result = true;
diff --git a/fs/afs/vl_probe.c b/fs/afs/vl_probe.c
index e3aa013c21779..081b7e5b13f58 100644
--- a/fs/afs/vl_probe.c
+++ b/fs/afs/vl_probe.c
@@ -92,8 +92,8 @@ responded:
 		}
 	}
 
-	rtt_us = rxrpc_kernel_get_srtt(call->net->socket, call->rxcall);
-	if (rtt_us < server->probe.rtt) {
+	if (rxrpc_kernel_get_srtt(call->net->socket, call->rxcall, &rtt_us) &&
+	    rtt_us < server->probe.rtt) {
 		server->probe.rtt = rtt_us;
 		alist->preferred = index;
 		have_result = true;
diff --git a/include/net/af_rxrpc.h b/include/net/af_rxrpc.h
index ab988940bf045..55b980b21f4b4 100644
--- a/include/net/af_rxrpc.h
+++ b/include/net/af_rxrpc.h
@@ -59,7 +59,7 @@ bool rxrpc_kernel_abort_call(struct socket *, struct rxrpc_call *,
 void rxrpc_kernel_end_call(struct socket *, struct rxrpc_call *);
 void rxrpc_kernel_get_peer(struct socket *, struct rxrpc_call *,
 			   struct sockaddr_rxrpc *);
-u32 rxrpc_kernel_get_srtt(struct socket *, struct rxrpc_call *);
+bool rxrpc_kernel_get_srtt(struct socket *, struct rxrpc_call *, u32 *);
 int rxrpc_kernel_charge_accept(struct socket *, rxrpc_notify_rx_t,
 			       rxrpc_user_attach_call_t, unsigned long, gfp_t,
 			       unsigned int);
diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c
index efce27802a74f..e011594adcd13 100644
--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -500,11 +500,21 @@ EXPORT_SYMBOL(rxrpc_kernel_get_peer);
  * rxrpc_kernel_get_srtt - Get a call's peer smoothed RTT
  * @sock: The socket on which the call is in progress.
  * @call: The call to query
+ * @_srtt: Where to store the SRTT value.
  *
- * Get the call's peer smoothed RTT.
+ * Get the call's peer smoothed RTT in uS.
  */
-u32 rxrpc_kernel_get_srtt(struct socket *sock, struct rxrpc_call *call)
+bool rxrpc_kernel_get_srtt(struct socket *sock, struct rxrpc_call *call,
+			   u32 *_srtt)
 {
-	return call->peer->srtt_us >> 3;
+	struct rxrpc_peer *peer = call->peer;
+
+	if (peer->rtt_count == 0) {
+		*_srtt = 1000000; /* 1S */
+		return false;
+	}
+
+	*_srtt = call->peer->srtt_us >> 3;
+	return true;
 }
 EXPORT_SYMBOL(rxrpc_kernel_get_srtt);