[PATCH] iommu/vt-d: Check for non-NULL domain on device release

[Eric Badger <ebadger@purestorage.com>]

In the kdump kernel, the IOMMU will operate in deferred_attach mode. In
this mode, info->domain may not yet be assigned by the time the
release_device function is called, which leads to the following crash in
the crashkernel:

    BUG: kernel NULL pointer dereference, address: 000000000000003c
    ...
    RIP: 0010:do_raw_spin_lock+0xa/0xa0
    ...
    _raw_spin_lock_irqsave+0x1b/0x30
    intel_iommu_release_device+0x96/0x170
    iommu_deinit_device+0x39/0xf0
    __iommu_group_remove_device+0xa0/0xd0
    iommu_bus_notifier+0x55/0xb0
    notifier_call_chain+0x5a/0xd0
    blocking_notifier_call_chain+0x41/0x60
    bus_notify+0x34/0x50
    device_del+0x269/0x3d0
    pci_remove_bus_device+0x77/0x100
    p2sb_bar+0xae/0x1d0
    ...
    i801_probe+0x423/0x740

Signed-off-by: Eric Badger <ebadger@purestorage.com>
---
 drivers/iommu/intel/iommu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 6fb5f6fceea1..26e450259889 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -3750,7 +3750,6 @@ static void domain_context_clear(struct device_domain_info *info)
 static void dmar_remove_one_dev_info(struct device *dev)
 {
 	struct device_domain_info *info = dev_iommu_priv_get(dev);
-	struct dmar_domain *domain = info->domain;
 	struct intel_iommu *iommu = info->iommu;
 	unsigned long flags;
 
@@ -3763,11 +3762,14 @@ static void dmar_remove_one_dev_info(struct device *dev)
 		domain_context_clear(info);
 	}
 
-	spin_lock_irqsave(&domain->lock, flags);
+	if (!info->domain)
+		return;
+
+	spin_lock_irqsave(&info->domain->lock, flags);
 	list_del(&info->link);
-	spin_unlock_irqrestore(&domain->lock, flags);
+	spin_unlock_irqrestore(&info->domain->lock, flags);
 
-	domain_detach_iommu(domain, iommu);
+	domain_detach_iommu(info->domain, iommu);
 	info->domain = NULL;
 }
 
-- 
2.34.1