[PATCH] iommu/vt-d: Fix a IOMMU perfmon warning when CPU hotplug
From: kan . liang
Date: Fri Mar 24 2023 - 11:11:48 EST
From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
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.
Use the dmar_global_lock to replace the RCU read lock when going through
the drhd list.
Fixes: 46284c6ceb5e ("iommu/vt-d: Support cpumask for IOMMU perfmon")
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
drivers/iommu/intel/perfmon.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/intel/perfmon.c b/drivers/iommu/intel/perfmon.c
index e17d9743a0d8..81c9554fb1dc 100644
--- a/drivers/iommu/intel/perfmon.c
+++ b/drivers/iommu/intel/perfmon.c
@@ -797,14 +797,14 @@ static int iommu_pmu_cpu_offline(unsigned int cpu)
else
target = -1;
- rcu_read_lock();
+ down_write(&dmar_global_lock);
for_each_iommu(iommu, drhd) {
if (!iommu->pmu)
continue;
perf_pmu_migrate_context(&iommu->pmu->pmu, cpu, target);
}
- rcu_read_unlock();
+ up_write(&dmar_global_lock);
return 0;
}
--
2.35.1