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Subject[PATCH 1/1] iommu/vt-d: Fix lockdep splat in iommu_flush_dev_iotlb()
Date
Lock(&iommu->lock) without disabling irq causes lockdep warnings.

[ 12.703950] ========================================================
[ 12.703962] WARNING: possible irq lock inversion dependency detected
[ 12.703975] 5.9.0-rc6+ #659 Not tainted
[ 12.703983] --------------------------------------------------------
[ 12.703995] systemd-udevd/284 just changed the state of lock:
[ 12.704007] ffffffffbd6ff4d8 (device_domain_lock){..-.}-{2:2}, at:
iommu_flush_dev_iotlb.part.57+0x2e/0x90
[ 12.704031] but this lock took another, SOFTIRQ-unsafe lock in the past:
[ 12.704043] (&iommu->lock){+.+.}-{2:2}
[ 12.704045]

and interrupts could create inverse lock ordering between
them.

[ 12.704073]
other info that might help us debug this:
[ 12.704085] Possible interrupt unsafe locking scenario:

[ 12.704097] CPU0 CPU1
[ 12.704106] ---- ----
[ 12.704115] lock(&iommu->lock);
[ 12.704123] local_irq_disable();
[ 12.704134] lock(device_domain_lock);
[ 12.704146] lock(&iommu->lock);
[ 12.704158] <Interrupt>
[ 12.704164] lock(device_domain_lock);
[ 12.704174]
*** DEADLOCK ***

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
drivers/iommu/intel/iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 1b7d390beb68..722545f61ba2 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2699,7 +2699,7 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
}

/* Setup the PASID entry for requests without PASID: */
- spin_lock(&iommu->lock);
+ spin_lock_irqsave(&iommu->lock, flags);
if (hw_pass_through && domain_type_is_si(domain))
ret = intel_pasid_setup_pass_through(iommu, domain,
dev, PASID_RID2PASID);
@@ -2709,7 +2709,7 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
else
ret = intel_pasid_setup_second_level(iommu, domain,
dev, PASID_RID2PASID);
- spin_unlock(&iommu->lock);
+ spin_unlock_irqrestore(&iommu->lock, flags);
if (ret) {
dev_err(dev, "Setup RID2PASID failed\n");
dmar_remove_one_dev_info(dev);
--
2.17.1
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