Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the devmap stall caused by missed xdp flush by counting the pending xdp redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was called under process context with preemption enabled. Simply disable preemption may silent the warning but be not enough since process may move between different CPUS during a batch which cause xdp_do_flush() misses some CPU where the process run previously. Consider the several fallouts, that commit was reverted. To fix the issue correctly, we can simply calling xdp_do_flush() immediately after xdp_do_redirect(), a side effect is that this removes any possibility of batching which could be addressed in the future.
Reported-by: Christoffer Dall <christoffer.d...@linaro.org> Fixes: 762c330d670e ("tuntap: add missing xdp flush") Signed-off-by: Jason Wang <jasow...@redhat.com> --- drivers/net/tun.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 2823a4a..a363ea2 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1662,6 +1662,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, get_page(alloc_frag->page); alloc_frag->offset += buflen; err = xdp_do_redirect(tun->dev, &xdp, xdp_prog); + xdp_do_flush_map(); if (err) goto err_redirect; rcu_read_unlock(); -- 2.7.4