Re: [PATCH v3 07/10] iommu: Use right way to retrieve iommu_ops

From: Lu Baolu
Date: Mon Feb 14 2022 - 21:03:26 EST


On 2/15/22 9:46 AM, Lu Baolu wrote:
On 2/14/22 8:49 PM, Joerg Roedel wrote:
On Mon, Feb 14, 2022 at 09:55:35AM +0800, Lu Baolu wrote:
+static inline const struct iommu_ops *dev_iommu_ops(struct device *dev)
+{
+    /*
+     * Assume that valid ops must be installed if iommu_probe_device()
+     * has succeeded. The device ops are essentially for internal use
+     * within the IOMMU subsystem itself, so we should be able to trust
+     * ourselves not to misuse the helper.
+     */
+    WARN_ON(!dev || !dev->iommu || !dev->iommu->iommu_dev ||
+        !dev->iommu->iommu_dev->ops);

There is no need for this WARN_ON, the code will oops anyway when one of
the pointers checked here is NULL.


We really don't need to WARN_ON intermediate null pointers. But I would
argue that we could add a WARN() on null dev->iommu->iommu_dev->ops, so
that callers have no need to check the returned ops.

Oh, sorry! We don't need to check null ops either. That will also result
in a null pointer reference oops in the caller.

So, yes. No need for this WARN_ON().

Best regards,
baolu