linux-kernel - [PATCH 6.8 705/715] bpf: report RCU QS in cpumap kthread

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Date: Sun, 24 Mar 2024 18:34:44 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Yan Zhai <yan@...udflare.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Jakub Kicinski <kuba@...nel.org>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH 6.8 705/715] bpf: report RCU QS in cpumap kthread

From: Yan Zhai <yan@...udflare.com>

[ 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@...nel.org>
Signed-off-by: Yan Zhai <yan@...udflare.com>
Acked-by: Paul E. McKenney <paulmck@...nel.org>
Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>
Link: https://lore.kernel.org/r/c17b9f1517e19d813da3ede5ed33ee18496bb5d8.1710877680.git.yan@cloudflare.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/cpumap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index ef82ffc90cbe9..8f1d390bcbdeb 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -262,6 +262,7 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
 static int cpu_map_kthread_run(void *data)
 {
 	struct bpf_cpu_map_entry *rcpu = data;
+	unsigned long last_qs = jiffies;
 
 	complete(&rcpu->kthread_running);
 	set_current_state(TASK_INTERRUPTIBLE);
@@ -287,10 +288,12 @@ 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();
 		}
 
-- 
2.43.0