[PATCH] iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc()

Lu Baolu
2023-03-14T05:19:48Z

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);
--
2.34.1