Patch "bpf: report RCU QS in cpumap kthread" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    bpf: report RCU QS in cpumap kthread

to the 5.4-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:
     bpf-report-rcu-qs-in-cpumap-kthread.patch
and it can be found in the queue-5.4 subdirectory.

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



commit d465f1628283ec4c61df0452e331f607e89d22f1
Author: Yan Zhai <yan@xxxxxxxxxxxxxx>
Date:   Tue Mar 19 13:44:40 2024 -0700

    bpf: report RCU QS in cpumap kthread
    
    [ Upstream commit 00bf63122459e87193ee7f1bc6161c83a525569f ]
    
    When there are heavy load, cpumap kernel threads can be busy polling
    packets from redirect queues and block out RCU tasks from reaching
    quiescent states. It is insufficient to just call cond_resched() in such
    context. Periodically raise a consolidated RCU QS before cond_resched
    fixes the problem.
    
    Fixes: 6710e1126934 ("bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP")
    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/c17b9f1517e19d813da3ede5ed33ee18496bb5d8.1710877680.git.yan@xxxxxxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index a367fc8503933..19be747f4e5ab 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -249,6 +249,7 @@ static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
 static int cpu_map_kthread_run(void *data)
 {
 	struct bpf_cpu_map_entry *rcpu = data;
+	unsigned long last_qs = jiffies;
 
 	set_current_state(TASK_INTERRUPTIBLE);
 
@@ -271,10 +272,12 @@ static int cpu_map_kthread_run(void *data)
 			if (__ptr_ring_empty(rcpu->queue)) {
 				schedule();
 				sched = 1;
+				last_qs = jiffies;
 			} else {
 				__set_current_state(TASK_RUNNING);
 			}
 		} else {
+			rcu_softirq_qs_periodic(last_qs);
 			sched = cond_resched();
 		}