FAILED: patch "[PATCH] iommu/arm-smmu: Defer probe of clients after smmu device" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 229e6ee43d2a160a1592b83aad620d6027084aad
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024120648-untie-unpack-b9ae@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 229e6ee43d2a160a1592b83aad620d6027084aad Mon Sep 17 00:00:00 2001
From: Pratyush Brahma <[email protected]>
Date: Fri, 4 Oct 2024 14:34:28 +0530
Subject: [PATCH] iommu/arm-smmu: Defer probe of clients after smmu device
bound

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:

T1:Smmu device probe T2: Client device probe

really_probe()
arm_smmu_device_probe()
iommu_device_register()

					really_probe()
					platform_dma_configure()
					of_dma_configure()
					of_dma_configure_id()
					of_iommu_configure()
					iommu_probe_device()
					iommu_init_device()
					arm_smmu_probe_device()
					arm_smmu_get_by_fwnode()
						driver_find_device_by_fwnode()
						driver_find_device()
						next_device()
						klist_next()
						    /* null ptr
						       assigned to smmu */
					/* null ptr dereference
					   while smmu->streamid_mask */

driver_bound()
klist_add_tail()

When this null smmu pointer is dereferenced later in arm_smmu_probe_device, the device crashes.

Fix this by deferring the probe of the client device until the smmu device has bound to the arm smmu driver.

index 8321962b3714..14618772a3d6 100644
@@ -1437,6 +1437,17 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
 			goto out_free;
 	} else {
 		smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode);
+
+		/*
+		 * Defer probe if the relevant SMMU instance hasn't finished
+		 * probing yet. This is a fragile hack and we'd ideally
+		 * avoid this race in the core code. Until that's ironed
+		 * out, however, this is the most pragmatic option on the
+		 * table.
+		 */
+		if (!smmu)
+			return ERR_PTR(dev_err_probe(dev, -EPROBE_DEFER,
+						"smmu dev has not bound yet\n"));
 	}
 
 	ret = -EINVAL;