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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.