Messages in this thread | | | Date | Wed, 15 Mar 2023 09:14:48 +0800 | Subject | Re: [PATCH] iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc() | From | Baolu Lu <> |
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On 3/14/23 11:54 PM, Jacob Pan wrote: > Hi BaoLu, > > On Tue, 14 Mar 2023 13:18:36 +0800, Lu Baolu <baolu.lu@linux.intel.com> > wrote: > >> The global rwsem dmar_global_lock was introduced by commit 3a5670e8ac932 >> ("iommu/vt-d: Introduce a rwsem to protect global data structures"). It >> is used to protect DMAR related global data from DMAR hotplug operations. >> >> Using dmar_global_lock in intel_irq_remapping_alloc() is unnecessary as >> the DMAR global data structures are not touched there. Remove it to avoid >> below lockdep warning. >> >> ====================================================== >> WARNING: possible circular locking dependency detected >> 6.3.0-rc2 #468 Not tainted >> ------------------------------------------------------ >> swapper/0/1 is trying to acquire lock: >> ff1db4cb40178698 (&domain->mutex){+.+.}-{3:3}, >> at: __irq_domain_alloc_irqs+0x3b/0xa0 >> >> but task is already holding lock: >> ffffffffa0c1cdf0 (dmar_global_lock){++++}-{3:3}, >> at: intel_iommu_init+0x58e/0x880 >> >> which lock already depends on the new lock. >> >> the existing dependency chain (in reverse order) is: >> >> -> #1 (dmar_global_lock){++++}-{3:3}: >> lock_acquire+0xd6/0x320 >> down_read+0x42/0x180 >> intel_irq_remapping_alloc+0xad/0x750 >> mp_irqdomain_alloc+0xb8/0x2b0 >> irq_domain_alloc_irqs_locked+0x12f/0x2d0 >> __irq_domain_alloc_irqs+0x56/0xa0 >> alloc_isa_irq_from_domain.isra.7+0xa0/0xe0 >> mp_map_pin_to_irq+0x1dc/0x330 >> setup_IO_APIC+0x128/0x210 >> apic_intr_mode_init+0x67/0x110 >> x86_late_time_init+0x24/0x40 >> start_kernel+0x41e/0x7e0 >> secondary_startup_64_no_verify+0xe0/0xeb >> >> -> #0 (&domain->mutex){+.+.}-{3:3}: >> check_prevs_add+0x160/0xef0 >> __lock_acquire+0x147d/0x1950 >> lock_acquire+0xd6/0x320 >> __mutex_lock+0x9c/0xfc0 >> __irq_domain_alloc_irqs+0x3b/0xa0 >> dmar_alloc_hwirq+0x9e/0x120 >> iommu_pmu_register+0x11d/0x200 >> intel_iommu_init+0x5de/0x880 >> pci_iommu_init+0x12/0x40 >> do_one_initcall+0x65/0x350 >> kernel_init_freeable+0x3ca/0x610 >> kernel_init+0x1a/0x140 >> ret_from_fork+0x29/0x50 >> >> other info that might help us debug this: >> >> Possible unsafe locking scenario: >> >> CPU0 CPU1 >> ---- ---- >> lock(dmar_global_lock); >> lock(&domain->mutex); >> lock(dmar_global_lock); >> lock(&domain->mutex); >> >> *** DEADLOCK *** >> >> Fixes: 9dbb8e3452ab ("irqdomain: Switch to per-domain locking") >> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> >> --- >> drivers/iommu/intel/irq_remapping.c | 6 ------ >> 1 file changed, 6 deletions(-) >> >> diff --git a/drivers/iommu/intel/irq_remapping.c >> b/drivers/iommu/intel/irq_remapping.c index 6d01fa078c36..df9e261af0b5 >> 100644 --- a/drivers/iommu/intel/irq_remapping.c >> +++ b/drivers/iommu/intel/irq_remapping.c >> @@ -311,14 +311,12 @@ static int set_ioapic_sid(struct irte *irte, int >> apic) if (!irte) >> return -1; >> >> - down_read(&dmar_global_lock); >> for (i = 0; i < MAX_IO_APICS; i++) { >> if (ir_ioapic[i].iommu && ir_ioapic[i].id == apic) { >> sid = (ir_ioapic[i].bus << 8) | >> ir_ioapic[i].devfn; break; >> } >> } >> - up_read(&dmar_global_lock); >> >> if (sid == 0) { >> pr_warn("Failed to set source-id of IOAPIC (%d)\n", >> apic); @@ -338,14 +336,12 @@ static int set_hpet_sid(struct irte *irte, >> u8 id) if (!irte) >> return -1; >> >> - down_read(&dmar_global_lock); >> for (i = 0; i < MAX_HPET_TBS; i++) { >> if (ir_hpet[i].iommu && ir_hpet[i].id == id) { >> sid = (ir_hpet[i].bus << 8) | ir_hpet[i].devfn; >> break; >> } >> } >> - up_read(&dmar_global_lock); >> >> if (sid == 0) { >> pr_warn("Failed to set source-id of HPET block (%d)\n", >> id); @@ -1339,9 +1335,7 @@ static int intel_irq_remapping_alloc(struct >> irq_domain *domain, if (!data) >> goto out_free_parent; >> >> - down_read(&dmar_global_lock); >> index = alloc_irte(iommu, &data->irq_2_iommu, nr_irqs); >> - up_read(&dmar_global_lock); >> if (index < 0) { >> pr_warn("Failed to allocate IRTE\n"); >> kfree(data); > Reviewed-by: Jacob Pan <jacob.jun.pan@linux.intel.com> > > slightly beyond the scope of this, do we need to take dmar_global_lock > below? shouldn't it be in single threaded context? > > down_write(&dmar_global_lock); > ret = dmar_dev_scope_init(); > up_write(&dmar_global_lock); > > return ret; > } > rootfs_initcall(ir_dev_scope_init);
Yes, agreed. This runs in a single threaded context. I will remove the locking in a cleanup patch.
Best regards, baolu
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