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Message-ID: <0b0e6fd6-b775-cdd0-c3c0-dc20056e07d2@linux.intel.com>
Date: Wed, 29 Mar 2023 09:12:50 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: joro@...tes.org, will@...nel.org, baolu.lu@...ux.intel.com,
dwmw2@...radead.org, robin.murphy@....com, iommu@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] iommu/vt-d: Fix a IOMMU perfmon warning when CPU
hotplug
On 2023-03-28 2:20 p.m., kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> A warning can be triggered when hotplug CPU 0.
> $ echo 0 > /sys/devices/system/cpu/cpu0/online
>
> [11958.737635] ------------[ cut here ]------------
> [11958.742882] Voluntary context switch within RCU read-side critical
> section!
> [11958.742891] WARNING: CPU: 0 PID: 19 at kernel/rcu/tree_plugin.h:318
> rcu_note_context_switch+0x4f4/0x580
> [11958.860095] RIP: 0010:rcu_note_context_switch+0x4f4/0x580
> [11958.960360] Call Trace:
> [11958.963161] <TASK>
> [11958.965565] ? perf_event_update_userpage+0x104/0x150
> [11958.971293] __schedule+0x8d/0x960
> [11958.975165] ? perf_event_set_state.part.82+0x11/0x50
> [11958.980891] schedule+0x44/0xb0
> [11958.984464] schedule_timeout+0x226/0x310
> [11958.989017] ? __perf_event_disable+0x64/0x1a0
> [11958.994054] ? _raw_spin_unlock+0x14/0x30
> [11958.998605] wait_for_completion+0x94/0x130
> [11959.003352] __wait_rcu_gp+0x108/0x130
> [11959.007616] synchronize_rcu+0x67/0x70
> [11959.011876] ? invoke_rcu_core+0xb0/0xb0
> [11959.016333] ? __bpf_trace_rcu_stall_warning+0x10/0x10
> [11959.022147] perf_pmu_migrate_context+0x121/0x370
> [11959.027478] iommu_pmu_cpu_offline+0x6a/0xa0
> [11959.032325] ? iommu_pmu_del+0x1e0/0x1e0
> [11959.036782] cpuhp_invoke_callback+0x129/0x510
> [11959.041825] cpuhp_thread_fun+0x94/0x150
> [11959.046283] smpboot_thread_fn+0x183/0x220
> [11959.050933] ? sort_range+0x20/0x20
> [11959.054902] kthread+0xe6/0x110
> [11959.058479] ? kthread_complete_and_exit+0x20/0x20
> [11959.063911] ret_from_fork+0x1f/0x30
> [11959.067982] </TASK>
> [11959.070489] ---[ end trace 0000000000000000 ]---
>
> The synchronize_rcu() will be invoked in the perf_pmu_migrate_context(),
> when migrating a PMU to a new CPU. However, the current for_each_iommu()
> is within RCU read-side critical section.
>
> Two methods were considered to fix the issue.
> - Use the dmar_global_lock to replace the RCU read lock when going
> through the drhd list. But it triggers a lockdep warning.
> - Use the cpuhp_setup_state_multi() to set up a dedicated state for each
> IOMMU PMU. The lock can be avoided.
>
> The latter method is implemented in this patch. Since each IOMMU PMU has
> a dedicated state, add cpuhp_node and cpu in struct iommu_pmu to track
> the state. The state can be dynamically allocated now. Remove the
> CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE.
>
> Fixes: 46284c6ceb5e ("iommu/vt-d: Support cpumask for IOMMU perfmon")
Forgot to add a tag. If the patch looks good, please add the below tag
when you pull the patch.
Reported-by: Ammy Yi <ammy.yi@...el.com>
Thanks,
Kan
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
> drivers/iommu/intel/iommu.h | 2 ++
> drivers/iommu/intel/perfmon.c | 68 ++++++++++++++++++++++-------------
> include/linux/cpuhotplug.h | 1 -
> 3 files changed, 46 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index d6df3b865812..694ab9b7d3e9 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -641,6 +641,8 @@ struct iommu_pmu {
> DECLARE_BITMAP(used_mask, IOMMU_PMU_IDX_MAX);
> struct perf_event *event_list[IOMMU_PMU_IDX_MAX];
> unsigned char irq_name[16];
> + struct hlist_node cpuhp_node;
> + int cpu;
> };
>
> #define IOMMU_IRQ_ID_OFFSET_PRQ (DMAR_UNITS_SUPPORTED)
> diff --git a/drivers/iommu/intel/perfmon.c b/drivers/iommu/intel/perfmon.c
> index e17d9743a0d8..e27bc954e866 100644
> --- a/drivers/iommu/intel/perfmon.c
> +++ b/drivers/iommu/intel/perfmon.c
> @@ -773,19 +773,34 @@ static void iommu_pmu_unset_interrupt(struct intel_iommu *iommu)
> iommu->perf_irq = 0;
> }
>
> -static int iommu_pmu_cpu_online(unsigned int cpu)
> +static int iommu_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)
> {
> + struct iommu_pmu *iommu_pmu = hlist_entry_safe(node, typeof(*iommu_pmu), cpuhp_node);
> +
> if (cpumask_empty(&iommu_pmu_cpu_mask))
> cpumask_set_cpu(cpu, &iommu_pmu_cpu_mask);
>
> + if (cpumask_test_cpu(cpu, &iommu_pmu_cpu_mask))
> + iommu_pmu->cpu = cpu;
> +
> return 0;
> }
>
> -static int iommu_pmu_cpu_offline(unsigned int cpu)
> +static int iommu_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)
> {
> - struct dmar_drhd_unit *drhd;
> - struct intel_iommu *iommu;
> - int target;
> + struct iommu_pmu *iommu_pmu = hlist_entry_safe(node, typeof(*iommu_pmu), cpuhp_node);
> + int target = cpumask_first(&iommu_pmu_cpu_mask);
> +
> + /*
> + * The iommu_pmu_cpu_mask has been updated when offline the CPU
> + * for the first iommu_pmu. Migrate the other iommu_pmu to the
> + * new target.
> + */
> + if ((target < nr_cpu_ids) && (target != iommu_pmu->cpu)) {
> + perf_pmu_migrate_context(&iommu_pmu->pmu, cpu, target);
> + iommu_pmu->cpu = target;
> + return 0;
> + }
>
> if (!cpumask_test_and_clear_cpu(cpu, &iommu_pmu_cpu_mask))
> return 0;
> @@ -795,45 +810,50 @@ static int iommu_pmu_cpu_offline(unsigned int cpu)
> if (target < nr_cpu_ids)
> cpumask_set_cpu(target, &iommu_pmu_cpu_mask);
> else
> - target = -1;
> + return 0;
>
> - rcu_read_lock();
> -
> - for_each_iommu(iommu, drhd) {
> - if (!iommu->pmu)
> - continue;
> - perf_pmu_migrate_context(&iommu->pmu->pmu, cpu, target);
> - }
> - rcu_read_unlock();
> + perf_pmu_migrate_context(&iommu_pmu->pmu, cpu, target);
> + iommu_pmu->cpu = target;
>
> return 0;
> }
>
> static int nr_iommu_pmu;
> +static enum cpuhp_state iommu_cpuhp_slot;
>
> static int iommu_pmu_cpuhp_setup(struct iommu_pmu *iommu_pmu)
> {
> int ret;
>
> - if (nr_iommu_pmu++)
> - return 0;
> + if (!nr_iommu_pmu) {
> + ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN,
> + "driver/iommu/intel/perfmon:online",
> + iommu_pmu_cpu_online,
> + iommu_pmu_cpu_offline);
> + if (ret < 0)
> + return ret;
> + iommu_cpuhp_slot = ret;
> + }
>
> - ret = cpuhp_setup_state(CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE,
> - "driver/iommu/intel/perfmon:online",
> - iommu_pmu_cpu_online,
> - iommu_pmu_cpu_offline);
> - if (ret)
> - nr_iommu_pmu = 0;
> + ret = cpuhp_state_add_instance(iommu_cpuhp_slot, &iommu_pmu->cpuhp_node);
> + if (ret) {
> + if (!nr_iommu_pmu)
> + cpuhp_remove_multi_state(iommu_cpuhp_slot);
> + return ret;
> + }
> + nr_iommu_pmu++;
>
> - return ret;
> + return 0;
> }
>
> static void iommu_pmu_cpuhp_free(struct iommu_pmu *iommu_pmu)
> {
> + cpuhp_state_remove_instance(iommu_cpuhp_slot, &iommu_pmu->cpuhp_node);
> +
> if (--nr_iommu_pmu)
> return;
>
> - cpuhp_remove_state(CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE);
> + cpuhp_remove_multi_state(iommu_cpuhp_slot);
> }
>
> void iommu_pmu_register(struct intel_iommu *iommu)
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index c6fab004104a..5b2f8147d1ae 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -218,7 +218,6 @@ enum cpuhp_state {
> CPUHP_AP_PERF_X86_CQM_ONLINE,
> CPUHP_AP_PERF_X86_CSTATE_ONLINE,
> CPUHP_AP_PERF_X86_IDXD_ONLINE,
> - CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE,
> CPUHP_AP_PERF_S390_CF_ONLINE,
> CPUHP_AP_PERF_S390_SF_ONLINE,
> CPUHP_AP_PERF_ARM_CCI_ONLINE,
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