| Message ID | 20220406155804.434493-1-maciej.fijalkowski@intel.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 8de8b71b787f38983d414d2dba169a3bfefa668a |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf] xsk: fix l2fwd for copy mode + busy poll combo | expand |
Hello: This patch was applied to bpf/bpf.git (master) by Daniel Borkmann <daniel@iogearbox.net>: On Wed, 6 Apr 2022 17:58:04 +0200 you wrote: > While checking AF_XDP copy mode combined with busy poll, strange > results were observed. rxdrop and txonly scenarios worked fine, but > l2fwd broke immediately. > > After a deeper look, it turned out that for l2fwd, Tx side was exiting > early due to xsk_no_wakeup() returning true and in the end > xsk_generic_xmit() was never called. Note that AF_XDP Tx in copy mode is > syscall steered, so the current behavior is broken. > > [...] Here is the summary with links: - [bpf] xsk: fix l2fwd for copy mode + busy poll combo https://git.kernel.org/bpf/bpf/c/8de8b71b787f You are awesome, thank you!
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 2c34caee0fd1..7d3a00cb24ec 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -639,7 +639,7 @@ static int __xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len if (sk_can_busy_loop(sk)) sk_busy_loop(sk, 1); /* only support non-blocking sockets */ - if (xsk_no_wakeup(sk)) + if (xs->zc && xsk_no_wakeup(sk)) return 0; pool = xs->pool;
While checking AF_XDP copy mode combined with busy poll, strange results were observed. rxdrop and txonly scenarios worked fine, but l2fwd broke immediately. After a deeper look, it turned out that for l2fwd, Tx side was exiting early due to xsk_no_wakeup() returning true and in the end xsk_generic_xmit() was never called. Note that AF_XDP Tx in copy mode is syscall steered, so the current behavior is broken. Txonly scenario only worked due to the fact that sk_mark_napi_id_once_xdp() was never called - since Rx side is not in the picture for this case and mentioned function is called in xsk_rcv_check(), sk::sk_napi_id was never set, which in turn meant that xsk_no_wakeup() was returning false (see the sk->sk_napi_id >= MIN_NAPI_ID check in there). To fix this, prefer busy poll in xsk_sendmsg() only when zero copy is enabled on a given AF_XDP socket. By doing so, busy poll in copy mode would not exit early on Tx side and eventually xsk_generic_xmit() will be called. Fixes: a0731952d9cd ("xsk: Add busy-poll support for {recv,send}msg()") Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com> --- net/xdp/xsk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)