DLPX-96594 fix linux-kernel updates to 6.17: export tcp symbols needed by connstat

[lyriclake]

Problem

After updating to kernel 6.17, connstat was failing to build with:

19:40:07  ERROR: modpost: "tcp_seq_start" [connstat.ko] undefined!
19:40:07  ERROR: modpost: "tcp_seq_stop" [connstat.ko] undefined!
19:40:07  ERROR: modpost: "tcp_seq_next" [connstat.ko] undefined!

The culprit is the upstream kernel commit:

commit 6dc4c25
Author: Eric Dumazet edumazet@google.com
Date: Wed Feb 12 13:24:17 2025 +0000

tcp: use EXPORT_IPV6_MOD_GPL
Use EXPORT_IPV6_MOD_GPL for symbols that don't need
to be exported unless CONFIG_IPV6=m
tcp_hashinfo and tcp_openreq_init_rwin() are no longer
used from any module anyway.
Signed-off-by: Eric Dumazet edumazet@google.com
Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com
Reviewed-by: Mateusz Polchlopek mateusz.polchlopek@intel.com
Link: https://patch.msgid.link/20250212132418.1524422-4-edumazet@google.com
Signed-off-by: Jakub Kicinski kuba@kernel.org

which only exports the needed symbols if CONFIG_IPV6=m (the default is CONFIG_IPV6=y).

This means the symbols are now exported if ipv6 support is build as a kernel module (m), but not when ipv6 support is built into the kernel (y). See debian/master/config/annotations:

CONFIG_IPV6     policy<{'amd64': 'y', 'arm64': 'y', 'armhf': 'y', 'ppc64el': 'y', 'riscv64': 'y', 's390x': 'y'}>
CONFIG_IPV6     note<'if this is a module we get a module load for every ipv6 packet'>

Solution

Rather than modifying our kernel build to make ipv6 a kernel module, I decided to patch tcp_ipv6.c to always export the 3 symbols connstat needs, partially reverting the upstream commit. This seemed like a less invasive / potentially impactful change.

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 84d3d556ed80..c20fff856746 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2831,7 +2831,7 @@ void *tcp_seq_start(struct seq_file *seq, loff_t *pos)
        st->last_pos = *pos;
        return rc;
 }
-EXPORT_IPV6_MOD(tcp_seq_start);
+EXPORT_SYMBOL(tcp_seq_start);

 void *tcp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
@@ -2862,7 +2862,7 @@ void *tcp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
        st->last_pos = *pos;
        return rc;
 }
-EXPORT_IPV6_MOD(tcp_seq_next);
+EXPORT_SYMBOL(tcp_seq_next);

 void tcp_seq_stop(struct seq_file *seq, void *v)
 {
@@ -2880,7 +2880,7 @@ void tcp_seq_stop(struct seq_file *seq, void *v)
                break;
        }
 }
-EXPORT_IPV6_MOD(tcp_seq_stop);
+EXPORT_SYMBOL(tcp_seq_stop);

 static void get_openreq4(const struct request_sock *req,
                         struct seq_file *f, int i)

Testing Done

https://selfservice-jenkins.eng-tools-prd.aws.delphixcloud.com/job/appliance-build-orchestrator-pre-push/13331/