linux-kernel - [PATCH] sched/smt: fix unbalance sched_smt

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Date:   Sat, 2 Sep 2023 15:46:09 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <mgorman@...e.de>, <bristot@...hat.com>,
        <vschneid@...hat.com>, <tglx@...utronix.de>,
        <yangyingliang@...wei.com>
Subject: [PATCH] sched/smt: fix unbalance sched_smt_present dec/inc

I got the following warn report while doing stress test:

jump label: negative count!
WARNING: CPU: 3 PID: 38 at kernel/jump_label.c:263 static_key_slow_try_dec+0x9d/0xb0
Call Trace:
 <TASK>
 __static_key_slow_dec_cpuslocked+0x16/0x70
 sched_cpu_deactivate+0x26e/0x2a0
 cpuhp_invoke_callback+0x3ad/0x10d0
 cpuhp_thread_fun+0x3f5/0x680
 smpboot_thread_fn+0x56d/0x8d0
 kthread+0x309/0x400
 ret_from_fork+0x41/0x70
 ret_from_fork_asm+0x1b/0x30
 </TASK>

Becaus when cpuset_cpu_inactive() fails in sched_cpu_deactivate(),
the cpu offline failed, but sched_smt_present is decreased before
calling sched_cpu_deactivate, it leads unbalance dec/inc, so fix
it by increasing sched_smt_present in the error path.

Fixes: c5511d03ec09 ("sched/smt: Make sched_smt_present track topology")
Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2299a5cfbfb9..b7ef2df36b75 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9745,6 +9745,10 @@ int sched_cpu_deactivate(unsigned int cpu)
 	sched_update_numa(cpu, false);
 	ret = cpuset_cpu_inactive(cpu);
 	if (ret) {
+#ifdef CONFIG_SCHED_SMT
+		if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+			static_branch_inc_cpuslocked(&sched_smt_present);
+#endif
 		balance_push_set(cpu, false);
 		set_cpu_active(cpu, true);
 		sched_update_numa(cpu, true);
-- 
2.25.1