On 2025/2/20 15:21, Tian, Kevin wrote:
From: Lu Baolubaolu.lu@linux.intel.com Sent: Tuesday, February 18, 2025 10:24 AM
Commit <d74169ceb0d2> ("iommu/vt-d: Allocate DMAR fault interrupts locally") moved the call to enable_drhd_fault_handling() to a code path that does not hold any lock while traversing the drhd list. Fix it by ensuring the dmar_global_lock lock is held when traversing the drhd list.
Without this fix, the following warning is triggered:
WARNING: suspicious RCU usage 6.14.0-rc3 #55 Not tainted
drivers/iommu/intel/dmar.c:2046 RCU-list traversed in non-reader section!! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 2 locks held by cpuhp/1/23: #0: ffffffff84a67c50 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 #1: ffffffff84a6a380 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 stack backtrace: CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 6.14.0-rc3 #55 Call Trace:
<TASK> dump_stack_lvl+0xb7/0xd0 lockdep_rcu_suspicious+0x159/0x1f0 ? __pfx_enable_drhd_fault_handling+0x10/0x10 enable_drhd_fault_handling+0x151/0x180 cpuhp_invoke_callback+0x1df/0x990 cpuhp_thread_fun+0x1ea/0x2c0 smpboot_thread_fn+0x1f5/0x2e0 ? __pfx_smpboot_thread_fn+0x10/0x10 kthread+0x12a/0x2d0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x4a/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>
Simply holding the lock in enable_drhd_fault_handling() will trigger a lock order splat. Avoid holding the dmar_global_lock when calling iommu_device_register(), which starts the device probe process.
Can you elaborate the splat issue? It's not intuitive to me with a quick read of the code and iommu_device_register() is not occurred in above calling stack.
The lockdep splat looks like below:
====================================================== WARNING: possible circular locking dependency detected 6.14.0-rc3-00002-g8e4617b46db1 #57 Not tainted ------------------------------------------------------ swapper/0/1 is trying to acquire lock: ffffffffa2a67c50 (cpu_hotplug_lock){++++}-{0:0}, at: iova_domain_init_rcaches.part.0+0x1d3/0x210
but task is already holding lock: ffff9f4a87b171c8 (&domain->iova_cookie->mutex){+.+.}-{4:4}, at: iommu_dma_init_domain+0x122/0x2e0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #4 (&domain->iova_cookie->mutex){+.+.}-{4:4}: __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 __mutex_lock+0xa5/0xce0 iommu_dma_init_domain+0x122/0x2e0 iommu_setup_dma_ops+0x65/0xe0 bus_iommu_probe+0x100/0x1d0 iommu_device_register+0xd6/0x130 intel_iommu_init+0x527/0x870 pci_iommu_init+0x17/0x60 do_one_initcall+0x7c/0x390 do_initcalls+0xe8/0x1e0 kernel_init_freeable+0x313/0x490 kernel_init+0x24/0x240 ret_from_fork+0x4a/0x60 ret_from_fork_asm+0x1a/0x30
-> #3 (&group->mutex){+.+.}-{4:4}: __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 __mutex_lock+0xa5/0xce0 bus_iommu_probe+0x95/0x1d0 iommu_device_register+0xd6/0x130 intel_iommu_init+0x527/0x870 pci_iommu_init+0x17/0x60 do_one_initcall+0x7c/0x390 do_initcalls+0xe8/0x1e0 kernel_init_freeable+0x313/0x490 kernel_init+0x24/0x240 ret_from_fork+0x4a/0x60 ret_from_fork_asm+0x1a/0x30
-> #2 (dmar_global_lock){++++}-{4:4}: __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 down_read+0x31/0x170 enable_drhd_fault_handling+0x27/0x1a0 cpuhp_invoke_callback+0x1e2/0x990 cpuhp_issue_call+0xac/0x2c0 __cpuhp_setup_state_cpuslocked+0x229/0x430 __cpuhp_setup_state+0xc3/0x260 irq_remap_enable_fault_handling+0x52/0x80 apic_intr_mode_init+0x59/0xf0 x86_late_time_init+0x29/0x50 start_kernel+0x642/0x7f0 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0x91/0xa0 common_startup_64+0x13e/0x148
-> #1 (cpuhp_state_mutex){+.+.}-{4:4}: __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 __mutex_lock+0xa5/0xce0 __cpuhp_setup_state_cpuslocked+0x81/0x430 __cpuhp_setup_state+0xc3/0x260 page_alloc_init_cpuhp+0x2d/0x40 mm_core_init+0x1e/0x3a0 start_kernel+0x277/0x7f0 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0x91/0xa0 common_startup_64+0x13e/0x148
-> #0 (cpu_hotplug_lock){++++}-{0:0}: check_prev_add+0xe2/0xc50 validate_chain+0x57c/0x800 __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 __cpuhp_state_add_instance+0x40/0x250 iova_domain_init_rcaches.part.0+0x1d3/0x210 iova_domain_init_rcaches+0x41/0x60 iommu_dma_init_domain+0x1af/0x2e0 iommu_setup_dma_ops+0x65/0xe0 bus_iommu_probe+0x100/0x1d0 iommu_device_register+0xd6/0x130 intel_iommu_init+0x527/0x870 pci_iommu_init+0x17/0x60 do_one_initcall+0x7c/0x390 do_initcalls+0xe8/0x1e0 kernel_init_freeable+0x313/0x490 kernel_init+0x24/0x240 ret_from_fork+0x4a/0x60 ret_from_fork_asm+0x1a/0x30
other info that might help us debug this:
Chain exists of: cpu_hotplug_lock --> &group->mutex --> &domain->iova_cookie->mutex
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&domain->iova_cookie->mutex); lock(&group->mutex); lock(&domain->iova_cookie->mutex); rlock(cpu_hotplug_lock);
*** DEADLOCK ***
3 locks held by swapper/0/1: #0: ffffffffa6442ab0 (dmar_global_lock){++++}-{4:4}, at: intel_iommu_init+0x42c/0x87 #1: ffff9f4a87b11310 (&group->mutex){+.+.}-{4:4}, at: bus_iommu_probe+0x95/0x1d0 #2: ffff9f4a87b171c8 (&domain->iova_cookie->mutex){+.+.}-{4:4}, at: iommu_dma_init_d
stack backtrace: CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.14.0-rc3-00002-g8e4617b46db1 #57 Call Trace: <TASK> dump_stack_lvl+0x93/0xd0 print_circular_bug+0x133/0x1c0 check_noncircular+0x12c/0x150 check_prev_add+0xe2/0xc50 ? add_chain_cache+0x108/0x460 validate_chain+0x57c/0x800 __lock_acquire+0x4a0/0xb50 lock_acquire+0xd1/0x2e0 ? iova_domain_init_rcaches.part.0+0x1d3/0x210 ? rcu_is_watching+0x11/0x50 __cpuhp_state_add_instance+0x40/0x250 ? iova_domain_init_rcaches.part.0+0x1d3/0x210 iova_domain_init_rcaches.part.0+0x1d3/0x210 iova_domain_init_rcaches+0x41/0x60 iommu_dma_init_domain+0x1af/0x2e0 iommu_setup_dma_ops+0x65/0xe0 bus_iommu_probe+0x100/0x1d0 iommu_device_register+0xd6/0x130 intel_iommu_init+0x527/0x870 ? __pfx_pci_iommu_init+0x10/0x10 pci_iommu_init+0x17/0x60 do_one_initcall+0x7c/0x390 do_initcalls+0xe8/0x1e0 kernel_init_freeable+0x313/0x490 ? __pfx_kernel_init+0x10/0x10 kernel_init+0x24/0x240 ? _raw_spin_unlock_irq+0x33/0x50 ret_from_fork+0x4a/0x60 ? __pfx_kernel_init+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>
Thanks, baolu