linux-kernel - [PATCH v2 1/3] sched/fair: Fix warning if NEXT

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Message-Id: <20241127055610.7076-2-adamli@os.amperecomputing.com>
Date: Wed, 27 Nov 2024 05:56:08 +0000
From: Adam Li <adamli@...amperecomputing.com>
To: peterz@...radead.org,
	mingo@...hat.com,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org
Cc: dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org,
	patches@...erecomputing.com,
	cl@...ux.com,
	christian.loehle@....com,
	vineethr@...ux.ibm.com,
	Adam Li <adamli@...amperecomputing.com>
Subject: [PATCH v2 1/3] sched/fair: Fix warning if NEXT_BUDDY enabled

Enabling NEXT_BUDDY triggers warning, and rcu stall:

[  124.977300] cfs_rq->next->sched_delayed
[  124.977310] WARNING: CPU: 51 PID: 2150 at kernel/sched/fair.c:5621 pick_task_fair+0x130/0x150
[  125.049547] CPU: 51 UID: 0 PID: 2150 Comm: kworker/51:1 Tainted: G            E      6.12.0.adam+ #1
<snip>
[  125.163561] Call trace:
[  125.165996]  pick_task_fair+0x130/0x150 (P)
[  125.170167]  pick_task_fair+0x130/0x150 (L)
[  125.174338]  pick_next_task_fair+0x48/0x3c0
[  125.178512]  __pick_next_task+0x4c/0x220
[  125.182426]  pick_next_task+0x44/0x980
[  125.186163]  __schedule+0x3d0/0x628
[  125.189645]  schedule+0x3c/0xe0
[  125.192776]  worker_thread+0x1a4/0x368
[  125.196516]  kthread+0xfc/0x110
[  125.199647]  ret_from_fork+0x10/0x20
[  125.203213] ---[ end trace 0000000000000000 ]---
<snip>
[  211.151849] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  211.159759] rcu:     (detected by 141, t=15003 jiffies, g=5629, q=26516 ncpus=384)
<snip>

Do not set next buddy if sched_delayed is set.

Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Signed-off-by: Adam Li <adamli@...amperecomputing.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fbdca89c677f..cd1188b7f3df 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8748,6 +8748,8 @@ static void set_next_buddy(struct sched_entity *se)
 			return;
 		if (se_is_idle(se))
 			return;
+		if (se->sched_delayed)
+			return;
 		cfs_rq_of(se)->next = se;
 	}
 }
-- 
2.25.1