[PATCH 4.16 094/272] rxrpc: Fix resend event time calculation

[Greg Kroah-Hartman]

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

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

From: Marc Dionne <marc.dionne@xxxxxxxxxxxx>

[ Upstream commit 59299aa1028fce051adbd25aaff7c387b865cd6d ]

Commit a158bdd3 ("rxrpc: Fix call timeouts") reworked the time calculation
for the next resend event.  For this calculation, "oldest" will be before
"now", so ktime_sub(oldest, now) will yield a negative value.  When passed
to nsecs_to_jiffies which expects an unsigned value, the end result will be
a very large value, and a resend event scheduled far into the future.  This
could cause calls to stall if some packets were lost.

Fix by ordering the arguments to ktime_sub correctly.

Fixes: a158bdd3247b ("rxrpc: Fix call timeouts")
Signed-off-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/rxrpc/call_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -225,7 +225,7 @@ static void rxrpc_resend(struct rxrpc_ca
 				       ktime_to_ns(ktime_sub(skb->tstamp, max_age)));
 	}
 
-	resend_at = nsecs_to_jiffies(ktime_to_ns(ktime_sub(oldest, now)));
+	resend_at = nsecs_to_jiffies(ktime_to_ns(ktime_sub(now, oldest)));
 	resend_at += jiffies + rxrpc_resend_timeout;
 	WRITE_ONCE(call->resend_at, resend_at);