16812c9655
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:
|
||
|---|---|---|
| .. | ||
| Kconfig | ||
| Makefile | ||
| cap_audit.c | ||
| cap_audit.h | ||
| debugfs.c | ||
| dmar.c | ||
| iommu.c | ||
| iommu.h | ||
| irq_remapping.c | ||
| pasid.c | ||
| pasid.h | ||
| perf.c | ||
| perf.h | ||
| perfmon.c | ||
| perfmon.h | ||
| svm.c | ||
| trace.c | ||
| trace.h | ||