Messages in this thread Patch in this message | | | From | kan.liang@linux ... | Subject | [PATCH] iommu/vt-d: Fix a IOMMU perfmon warning when CPU hotplug | Date | Fri, 24 Mar 2023 08:11:06 -0700 |
| |
From: Kan Liang <kan.liang@linux.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.
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@linux.intel.com> --- 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
| |