net: increase IP_TUNNEL_RECURSION_LIMIT to 5

In configurations with multiple tunnel layers and MPLS lwtunnel routing, a
single tunnel hop can increment the counter beyond this limit. This causes
packets to be dropped with the "Dead loop on virtual device" message even
when a routing loop doesn't exist.

Increase IP_TUNNEL_RECURSION_LIMIT from 4 to 5 to handle this use-case.

Fixes: 6f1a914 ("net: add xmit recursion limit to tunnel xmit functions")
Link: https://lore.kernel.org/netdev/[email protected]/
Signed-off-by: Chris J Arges <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: arges

include/net/ip_tunnels.h

@@ -32,7 +32,7 @@
  * recursion involves route lookups and full IP output, consuming much
  * more stack per level, so a lower limit is needed.
  */
-#define IP_TUNNEL_RECURSION_LIMIT	4
+#define IP_TUNNEL_RECURSION_LIMIT	5
 
 /* Keep error state on tunnel for 30 sec */
 #define IPTUNNEL_ERR_TIMEO	(30*HZ)