bpf: avoid preempt enable/disable in sockmap using tcp_skb_cb region

SK_SKB BPF programs are run from the socket/tcp context but early in
the stack before much of the TCP metadata is needed in tcp_skb_cb. So
we can use some unused fields to place BPF metadata needed for SK_SKB
programs when implementing the redirect function.

This allows us to drop the preempt disable logic. It does however
require an API change so sk_redirect_map() has been updated to
additionally provide ctx_ptr to skb. Note, we do however continue to
disable/enable preemption around actual BPF program running to account
for map updates.

Signed-off-by: John Fastabend <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index d29e58fde364..818a0b26249e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -728,7 +728,7 @@ void xdp_do_flush_map(void);
 void bpf_warn_invalid_xdp_action(u32 act);
 void bpf_warn_invalid_xdp_redirect(u32 ifindex);
 
-struct sock *do_sk_redirect_map(void);
+struct sock *do_sk_redirect_map(struct sk_buff *skb);
 
 #ifdef CONFIG_BPF_JIT
 extern int bpf_jit_enable;