tun: Use netif_receive_skb instead of netif_rx

This patch changes tun.c to call netif_receive_skb instead of netif_rx
when a packet is received (if CONFIG_4KSTACKS is not enabled to avoid
stack exhaustion). The difference between the two is that netif_rx queues
the packet into the backlog, and netif_receive_skb proccesses the packet
in the current context.

This patch is required for syzkaller [1] to collect coverage from packet
receive paths, when a packet being received through tun (syzkaller collects
coverage per process in the process context).

As mentioned by Eric this change also speeds up tun/tap. As measured by
Peter it speeds up his closed-loop single-stream tap/OVS benchmark by
about 23%, from 700k packets/second to 867k packets/second.

A similar patch was introduced back in 2010 [2, 3], but the author found
out that the patch doesn't help with the task he had in mind (for cgroups
to shape network traffic based on the original process) and decided not to
go further with it. The main concern back then was about possible stack
exhaustion with 4K stacks.

[1] https://github.com/google/syzkaller

[2] https://www.spinics.net/lists/netdev/thrd440.html#130570

[3] https://www.spinics.net/lists/netdev/msg130570.html

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a3ac8636f3ba915cc8a152f5db259c3200f3714b..a569e61bc1d9e6647b8b60ef700efdef52b58de5 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1286,7 +1286,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
        skb_probe_transport_header(skb, 0);
 
        rxhash = skb_get_hash(skb);
+#ifndef CONFIG_4KSTACKS
+       local_bh_disable();
+       netif_receive_skb(skb);
+       local_bh_enable();
+#else
        netif_rx_ni(skb);
+#endif
 
        stats = get_cpu_ptr(tun->pcpu_stats);
        u64_stats_update_begin(&stats->syncp);