Patch "net: report RCU QS on threaded NAPI repolling" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net: report RCU QS on threaded NAPI repolling

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-report-rcu-qs-on-threaded-napi-repolling.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 48cd3f8ba3b4a9a47361edaeef904310ba4106c7
Author: Yan Zhai <yan@xxxxxxxxxxxxxx>
Date:   Tue Mar 19 13:44:37 2024 -0700

    net: report RCU QS on threaded NAPI repolling
    
    [ 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@xxxxxxxxxx>
    Signed-off-by: Yan Zhai <yan@xxxxxxxxxxxxxx>
    Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Acked-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/4c3b0d3f32d3b18949d75b18e5e1d9f13a24f025.1710877680.git.yan@xxxxxxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/dev.c b/net/core/dev.c
index 9a48a7e26cf46..65284eeec7de5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6645,6 +6645,8 @@ static int napi_threaded_poll(void *data)
 	void *have;
 
 	while (!napi_thread_wait(napi)) {
+		unsigned long last_qs = jiffies;
+
 		for (;;) {
 			bool repoll = false;
 
@@ -6659,6 +6661,7 @@ static int napi_threaded_poll(void *data)
 			if (!repoll)
 				break;
 
+			rcu_softirq_qs_periodic(last_qs);
 			cond_resched();
 		}
 	}