tuntap: disable preemption during XDP processing (23e43f07) · Commits · 戴 / test

Except for tuntap, all other drivers' XDP was implemented at NAPI poll() routine in a bh. This guarantees all XDP operation were done at the same CPU which is required by e.g BFP_MAP_TYPE_PERCPU_ARRAY. But for tuntap, we do it in process context and we try to protect XDP processing by RCU reader lock. This is insufficient since CONFIG_PREEMPT_RCU can preempt the RCU reader critical section which breaks the assumption that all XDP were processed in the same CPU. Fixing this by simply disabling preemption during XDP processing. Fixes: ("tap: XDP support") Signed-off-by:

Jason Wang <jasowang@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

drivers/net/tun.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -1642,6 +1642,7 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		else
		*skb_xdp = 0;

		preempt_disable();
		rcu_read_lock();
		xdp_prog = rcu_dereference(tun->xdp_prog);
		if (xdp_prog && !*skb_xdp) {
		@@ -1665,6 +1666,7 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		if (err)
		goto err_redirect;
		rcu_read_unlock();
		preempt_enable();
		return NULL;
		case XDP_TX:
		xdp_xmit = true;
		@@ -1686,6 +1688,7 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		skb = build_skb(buf, buflen);
		if (!skb) {
		rcu_read_unlock();
		preempt_enable();
		return ERR_PTR(-ENOMEM);
		}

		@@ -1698,10 +1701,12 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		skb->dev = tun->dev;
		generic_xdp_tx(skb, xdp_prog);
		rcu_read_unlock();
		preempt_enable();
		return NULL;
		}

		rcu_read_unlock();
		preempt_enable();

		return skb;

		@@ -1709,6 +1714,7 @@ err_redirect:
		put_page(alloc_frag->page);
		err_xdp:
		rcu_read_unlock();
		preempt_enable();
		this_cpu_inc(tun->pcpu_stats->rx_dropped);
		return NULL;
		}

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