Re: [PATCH v2] iommu/arm-smmu: Defer probe of clients after smmu device bound

[Robin Murphy <robin.murphy@arm.com>]

On 29/10/2024 4:15 pm, Will Deacon wrote:
> On Fri, 04 Oct 2024 14:34:28 +0530, Pratyush Brahma wrote:
>> Null pointer dereference occurs due to a race between smmu
>> driver probe and client driver probe, when of_dma_configure()
>> for client is called after the iommu_device_register() for smmu driver
>> probe has executed but before the driver_bound() for smmu driver
>> has been called.
>>
>> Following is how the race occurs:
>>
>> [...]
> 
> Applied to will (for-joerg/arm-smmu/updates), thanks!
> 
> [1/1] iommu/arm-smmu: Defer probe of clients after smmu device bound
>        https://git.kernel.org/will/c/229e6ee43d2a

I've finally got to the point of proving to myself that this isn't the
right fix, since once we do get __iommu_probe_device() working properly
in the correct order, iommu_device_register() then runs into the same
condition itself. Diff below should make this issue go away - I'll write
up proper patches once I've tested it a little more.

Thanks,
Robin.

----->8-----
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 737c5b882355..b7dcb1494aa4 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3171,8 +3171,8 @@ static struct platform_driver arm_smmu_driver;
  static
  struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle *fwnode)
  {
-	struct device *dev = driver_find_device_by_fwnode(&arm_smmu_driver.driver,
-							  fwnode);
+	struct device *dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
+
  	put_device(dev);
  	return dev ? dev_get_drvdata(dev) : NULL;
  }
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index 8321962b3714..aba315aa6848 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -1411,8 +1411,8 @@ static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
  static
  struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle *fwnode)
  {
-	struct device *dev = driver_find_device_by_fwnode(&arm_smmu_driver.driver,
-							  fwnode);
+	struct device *dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
+
  	put_device(dev);
  	return dev ? dev_get_drvdata(dev) : NULL;
  }
@@ -2232,21 +2232,6 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
  					i, irq);
  	}
  
-	err = iommu_device_sysfs_add(&smmu->iommu, smmu->dev, NULL,
-				     "smmu.%pa", &smmu->ioaddr);
-	if (err) {
-		dev_err(dev, "Failed to register iommu in sysfs\n");
-		return err;
-	}
-
-	err = iommu_device_register(&smmu->iommu, &arm_smmu_ops,
-				    using_legacy_binding ? NULL : dev);
-	if (err) {
-		dev_err(dev, "Failed to register iommu\n");
-		iommu_device_sysfs_remove(&smmu->iommu);
-		return err;
-	}
-
  	platform_set_drvdata(pdev, smmu);
  
  	/* Check for RMRs and install bypass SMRs if any */
@@ -2255,6 +2240,18 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
  	arm_smmu_device_reset(smmu);
  	arm_smmu_test_smr_masks(smmu);
  
+	err = iommu_device_sysfs_add(&smmu->iommu, smmu->dev, NULL,
+				     "smmu.%pa", &smmu->ioaddr);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to register iommu in sysfs\n");
+
+	err = iommu_device_register(&smmu->iommu, &arm_smmu_ops,
+				    using_legacy_binding ? NULL : dev);
+	if (err) {
+		iommu_device_sysfs_remove(&smmu->iommu);
+		return dev_err_probe(dev, err, "Failed to register iommu\n");
+	}
+
  	/*
  	 * We want to avoid touching dev->power.lock in fastpaths unless
  	 * it's really going to do something useful - pm_runtime_enabled()