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Date:   Thu, 8 Jun 2023 13:40:39 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Junhao He <hejunhao3@huawei.com>, will@kernel.org
Cc:     jonathan.cameron@huawei.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linuxarm@huawei.com, yangyicong@huawei.com, shenyang39@huawei.com,
        prime.zeng@hisilicon.com
Subject: Re: [PATCH] drivers/perf: hisi: Don't migrate perf to the CPU going
 to teardown
Message-ID: <ZIHMRzLcff8lx6cE@FVFF77S0Q05N>
References: <20230608114326.27649-1-hejunhao3@huawei.com>
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On Thu, Jun 08, 2023 at 07:43:26PM +0800, Junhao He wrote:
> The driver needs to migrate the perf context if the current using CPU going
> to teardown. By the time calling the cpuhp::teardown() callback the
> cpu_online_mask() hasn't updated yet and still includes the CPU going to
> teardown. In current driver's implementation we may migrate the context
> to the teardown CPU and leads to the below calltrace:
> 
> ...
> [  368.104662][  T932] task:cpuhp/0         state:D stack:    0 pid:   15 ppid:     2 flags:0x00000008
> [  368.113699][  T932] Call trace:
> [  368.116834][  T932]  __switch_to+0x7c/0xbc
> [  368.120924][  T932]  __schedule+0x338/0x6f0
> [  368.125098][  T932]  schedule+0x50/0xe0
> [  368.128926][  T932]  schedule_preempt_disabled+0x18/0x24
> [  368.134229][  T932]  __mutex_lock.constprop.0+0x1d4/0x5dc
> [  368.139617][  T932]  __mutex_lock_slowpath+0x1c/0x30
> [  368.144573][  T932]  mutex_lock+0x50/0x60
> [  368.148579][  T932]  perf_pmu_migrate_context+0x84/0x2b0
> [  368.153884][  T932]  hisi_pcie_pmu_offline_cpu+0x90/0xe0 [hisi_pcie_pmu]
> [  368.160579][  T932]  cpuhp_invoke_callback+0x2a0/0x650
> [  368.165707][  T932]  cpuhp_thread_fun+0xe4/0x190
> [  368.170316][  T932]  smpboot_thread_fn+0x15c/0x1a0
> [  368.175099][  T932]  kthread+0x108/0x13c
> [  368.179012][  T932]  ret_from_fork+0x10/0x18
> ...
> 
> Use function cpumask_any_but() to find one correct active cpu to fixes
> this issue.
> 
> Fixes: 8404b0fbc7fb ("drivers/perf: hisi: Add driver for HiSilicon PCIe PMU")
> Signed-off-by: Junhao He <hejunhao3@huawei.com>

Acked-by: Mark Rutland <mark.rutland@arm.com>

I assume that Will can pick this up.

I did a quick check, and all other perf drivers seem to do the right thing
here, either using cpumask_any_but(), or generating a temporary mask with the
cpu being offlined removed.

Mark.

> ---
>  drivers/perf/hisilicon/hisi_pcie_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/hisilicon/hisi_pcie_pmu.c b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> index 0bc8dc36aff5..14f8b4b03337 100644
> --- a/drivers/perf/hisilicon/hisi_pcie_pmu.c
> +++ b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> @@ -683,7 +683,7 @@ static int hisi_pcie_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
>  
>  	pcie_pmu->on_cpu = -1;
>  	/* Choose a new CPU from all online cpus. */
> -	target = cpumask_first(cpu_online_mask);
> +	target = cpumask_any_but(cpu_online_mask, cpu);
>  	if (target >= nr_cpu_ids) {
>  		pci_err(pcie_pmu->pdev, "There is no CPU to set\n");
>  		return 0;
> -- 
> 2.30.0
>