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iommu/vt-d: Fix an IOMMU perfmon warning when CPU hotplug 

A warning can be triggered when hotplug CPU 0.
$ echo 0 > /sys/devices/system/cpu/cpu0/online

 ------------[ cut here ]------------
 Voluntary context switch within RCU read-side critical section!
 WARNING: CPU: 0 PID: 19 at kernel/rcu/tree_plugin.h:318
          rcu_note_context_switch+0x4f4/0x580
 RIP: 0010:rcu_note_context_switch+0x4f4/0x580
 Call Trace:
  <TASK>
  ? perf_event_update_userpage+0x104/0x150
  __schedule+0x8d/0x960
  ? perf_event_set_state.part.82+0x11/0x50
  schedule+0x44/0xb0
  schedule_timeout+0x226/0x310
  ? __perf_event_disable+0x64/0x1a0
  ? _raw_spin_unlock+0x14/0x30
  wait_for_completion+0x94/0x130
  __wait_rcu_gp+0x108/0x130
  synchronize_rcu+0x67/0x70
  ? invoke_rcu_core+0xb0/0xb0
  ? __bpf_trace_rcu_stall_warning+0x10/0x10
  perf_pmu_migrate_context+0x121/0x370
  iommu_pmu_cpu_offline+0x6a/0xa0
  ? iommu_pmu_del+0x1e0/0x1e0
  cpuhp_invoke_callback+0x129/0x510
  cpuhp_thread_fun+0x94/0x150
  smpboot_thread_fn+0x183/0x220
  ? sort_range+0x20/0x20
  kthread+0xe6/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x1f/0x30
  </TASK>
 ---[ 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: 46284c6ceb ("iommu/vt-d: Support cpumask for IOMMU perfmon")
Reported-by: Ammy Yi <ammy.yi@intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20230328182028.1366416-1-kan.liang@linux.intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20230329134721.469447-4-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Kan Liang 2023-03-29 21:47:21 +08:00 committed by Joerg Roedel
parent bfd3c6b9fa
commit 16812c9655
3 changed files with 46 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/iommu/intel/iommu.h
View File

@ -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)

68
drivers/iommu/intel/perfmon.c
View File

@ -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)

1
include/linux/cpuhotplug.h
View File

@ -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,