On architectures defining _HAVE_ARCH_IPV6_CSUM, we get csum_ipv6_magic() defined by means of arch checksum.h headers. On other architectures, we actually need to include net/ip6_checksum.h to be able to use it. Without this include, building with defconfig breaks at least for s390. Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Fixes: 4cb47a8644cc ("tunnels: PMTU discovery support for directly bridged IP packets") Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx> --- I'm submitting this for net-next despite the fact it's closed, as the offending code isn't merged to net.git yet. Should I rather submit this to... linux-next? Re-sending as original copy seems to be stuck in some SMTP queue. net/ipv4/ip_tunnel_core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c index 9ddee2a0c66d..75c6013ff9a4 100644 --- a/net/ipv4/ip_tunnel_core.c +++ b/net/ipv4/ip_tunnel_core.c @@ -25,6 +25,7 @@ #include <net/protocol.h> #include <net/ip_tunnels.h> #include <net/ip6_tunnel.h> +#include <net/ip6_checksum.h> #include <net/arp.h> #include <net/checksum.h> #include <net/dsfield.h> -- 2.27.0