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Message-ID: <5fce12a8.c23.190733d53e9.Coremail.yangyingliang@huaweicloud.com>
Date: Tue, 2 Jul 2024 19:38:37 +0800 (GMT+08:00)
From: yangyingliang@...weicloud.com
To: "Peter Zijlstra" <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, 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, 
	yu.c.chen@...el.com, tim.c.chen@...ux.intel.com, 
	yangyingliang@...wei.com, liwei391@...wei.com
Subject: Re: [PATCH resend] sched/smt: fix unbalance sched_smt_present
 dec/inc




&gt; -----Original Messages-----
&gt; From: "Peter Zijlstra" <peterz@...radead.org>
&gt; Sent Time: 2024-07-02 16:44:18 (Tuesday)
&gt; To: "Yang Yingliang" <yangyingliang@...weicloud.com>
&gt; Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, 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, yu.c.chen@...el.com, tim.c.chen@...ux.intel.com, yangyingliang@...wei.com, liwei391@...wei.com
&gt; Subject: Re: [PATCH resend] sched/smt: fix unbalance sched_smt_present dec/inc
&gt; 
&gt; On Tue, Jul 02, 2024 at 04:11:28PM +0800, Yang Yingliang wrote:
&gt; &gt; From: Yang Yingliang <yangyingliang@...wei.com>
&gt; &gt; 
&gt; &gt; I got the following warn report while doing stress test:
&gt; &gt; 
&gt; &gt; jump label: negative count!
&gt; &gt; WARNING: CPU: 3 PID: 38 at kernel/jump_label.c:263 static_key_slow_try_dec+0x9d/0xb0
&gt; &gt; Call Trace:
&gt; &gt;  <task>
&gt; &gt;  __static_key_slow_dec_cpuslocked+0x16/0x70
&gt; &gt;  sched_cpu_deactivate+0x26e/0x2a0
&gt; &gt;  cpuhp_invoke_callback+0x3ad/0x10d0
&gt; &gt;  cpuhp_thread_fun+0x3f5/0x680
&gt; &gt;  smpboot_thread_fn+0x56d/0x8d0
&gt; &gt;  kthread+0x309/0x400
&gt; &gt;  ret_from_fork+0x41/0x70
&gt; &gt;  ret_from_fork_asm+0x1b/0x30
&gt; &gt;  </task>
&gt; &gt; 
&gt; &gt; Because when cpuset_cpu_inactive() fails in sched_cpu_deactivate(),
&gt; &gt; the cpu offline failed, but sched_smt_present is decremented before
&gt; &gt; calling sched_cpu_deactivate(), it leads to unbalanced dec/inc, so
&gt; &gt; fix it by incrementing sched_smt_present in the error path.
&gt; &gt; 
&gt; &gt; Fixes: c5511d03ec09 ("sched/smt: Make sched_smt_present track topology")
&gt; &gt; Reviewed-by: Chen Yu <yu.c.chen@...el.com>
&gt; &gt; Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>
&gt; &gt; Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
&gt; &gt; ---
&gt; &gt;  kernel/sched/core.c | 4 ++++
&gt; &gt;  1 file changed, 4 insertions(+)
&gt; &gt; 
&gt; &gt; diff --git a/kernel/sched/core.c b/kernel/sched/core.c
&gt; &gt; index bcf2c4cc0522..5ab6717b57e0 100644
&gt; &gt; --- a/kernel/sched/core.c
&gt; &gt; +++ b/kernel/sched/core.c
&gt; &gt; @@ -9756,6 +9756,10 @@ int sched_cpu_deactivate(unsigned int cpu)
&gt; &gt;  	sched_update_numa(cpu, false);
&gt; &gt;  	ret = cpuset_cpu_inactive(cpu);
&gt; &gt;  	if (ret) {
&gt; &gt; +#ifdef CONFIG_SCHED_SMT
&gt; &gt; +		if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
&gt; &gt; +			static_branch_inc_cpuslocked(&amp;sched_smt_present);
&gt; &gt; +#endif
&gt; &gt;  		balance_push_set(cpu, false);
&gt; &gt;  		set_cpu_active(cpu, true);
&gt; &gt;  		sched_update_numa(cpu, true);
&gt; 
&gt; Yes, does indeed appear needed, however!, when I look at
&gt; what else goes before this failure, should we not also call
&gt; set_rq_online() and things like that?
Yes, set_rq_online() is needed in the error path. I will send a new patch to add this.

&gt; 
&gt; That is, can we rework things to be less fragile by sharing code between
&gt; this error path and sched_cpu_activate() ?
</yangyingliang@...wei.com></tim.c.chen@...ux.intel.com></yu.c.chen@...el.com></yangyingliang@...wei.com></yangyingliang@...weicloud.com></peterz@...radead.org>

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