Messages in this thread | | | Date | Tue, 14 Mar 2023 08:54:24 -0700 | From | Jacob Pan <> | Subject | Re: [PATCH] iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc() |
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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);
Thanks,
Jacob
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