From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Jason Wang To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: mst@redhat.com, christoffer.dall@linaro.org, sergei.shtylyov@cogentembedded.com, Jason Wang Subject: [PATCH net v3 2/2] tuntap: correctly add the missing xdp flush Date: Thu, 22 Feb 2018 17:36:46 +0800 Message-Id: <1519292206-6384-2-git-send-email-jasowang@redhat.com> In-Reply-To: <1519292206-6384-1-git-send-email-jasowang@redhat.com> References: <1519292206-6384-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 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 to BUG() since xdp_do_flush() was called in the process context with preemption enabled. Simply disabling preemption may silence 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 fallouts, that commit was reverted. To fix the issue correctly, we can simply call 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 Fixes: 762c330d670e ("tuntap: add missing xdp flush") Signed-off-by: Jason Wang --- 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