[PATCH v3 1/5] iommu: Lock group->mutex in iommu_deferred_attach

Nicolin Chen
2025-08-11T23:00:32Z

The iommu_deferred_attach() is a runtime asynchronous function called by
iommu-dma function, which could race against other attach functions if it
accesses something in the dev->iommu_group.

So, grab the mutex to guard __iommu_attach_device() like other callers.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/iommu.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 060ebe330ee16..1e0116bce0762 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2144,10 +2144,17 @@ EXPORT_SYMBOL_GPL(iommu_attach_device);

int iommu_deferred_attach(struct device *dev, struct iommu_domain *domain)
{
- if (dev->iommu && dev->iommu->attach_deferred)
- return __iommu_attach_device(domain, dev);
+ /*
+ * This is called on the dma mapping fast path so avoid locking. This is
+ * racy, but we have an expectation that the driver will setup its DMAs
+ * inside probe while being single threaded to avoid racing.
+ */
+ if (!dev->iommu || !dev->iommu->attach_deferred)
+ return 0;

- return 0;
+ guard(mutex)(&dev->iommu_group->mutex);
+
+ return __iommu_attach_device(domain, dev);
}

void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
--
2.43.0