From: Yan Zhai yan@cloudflare.com
[ Upstream commit d6dbbb11247c71203785a2c9da474c36f4b19eae ]
NAPI threads can keep polling packets under load. Currently it is only calling cond_resched() before repolling, but it is not sufficient to clear out the holdout of RCU tasks, which prevent BPF tracing programs from detaching for long period. This can be reproduced easily with following set up:
ip netns add test1 ip netns add test2
ip -n test1 link add veth1 type veth peer name veth2 netns test2
ip -n test1 link set veth1 up ip -n test1 link set lo up ip -n test2 link set veth2 up ip -n test2 link set lo up
ip -n test1 addr add 192.168.1.2/31 dev veth1 ip -n test1 addr add 1.1.1.1/32 dev lo ip -n test2 addr add 192.168.1.3/31 dev veth2 ip -n test2 addr add 2.2.2.2/31 dev lo
ip -n test1 route add default via 192.168.1.3 ip -n test2 route add default via 192.168.1.2
for i in `seq 10 210`; do for j in `seq 10 210`; do ip netns exec test2 iptables -I INPUT -s 3.3.$i.$j -p udp --dport 5201 done done
ip netns exec test2 ethtool -K veth2 gro on ip netns exec test2 bash -c 'echo 1 > /sys/class/net/veth2/threaded' ip netns exec test1 ethtool -K veth1 tso off
Then run an iperf3 client/server and a bpftrace script can trigger it:
ip netns exec test2 iperf3 -s -B 2.2.2.2 >/dev/null& ip netns exec test1 iperf3 -c 2.2.2.2 -B 1.1.1.1 -u -l 1500 -b 3g -t 100 >/dev/null& bpftrace -e 'kfunc:__napi_poll{@=count();} interval:s:1{exit();}'
Report RCU quiescent states periodically will resolve the issue.
Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support") Reviewed-by: Jesper Dangaard Brouer hawk@kernel.org Signed-off-by: Yan Zhai yan@cloudflare.com Acked-by: Paul E. McKenney paulmck@kernel.org Acked-by: Jesper Dangaard Brouer hawk@kernel.org Link: https://lore.kernel.org/r/4c3b0d3f32d3b18949d75b18e5e1d9f13a24f025.171087768... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/dev.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/core/dev.c b/net/core/dev.c index 1e41971c06177..f80bc2ca888aa 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -7143,6 +7143,8 @@ static int napi_threaded_poll(void *data) void *have;
while (!napi_thread_wait(napi)) { + unsigned long last_qs = jiffies; + for (;;) { bool repoll = false;
@@ -7157,6 +7159,7 @@ static int napi_threaded_poll(void *data) if (!repoll) break;
+ rcu_softirq_qs_periodic(last_qs); cond_resched(); } }