[PATCH RFC v5 1/6] iommu/arm-smmu-v3: Don't rb_erase() a never-inserted stream node

["Peng Fan (OSS)" <peng.fan@oss.nxp.com>]

From: Nicolin Chen <nicolinc@nvidia.com>

arm_smmu_insert_master() skips inserting a stream whose StreamID duplicates
one the same master already owns (bridged PCI devices can present duplicate
IDs), leaving that master->streams[i].node zeroed and unlinked from the
smmu->streams rb-tree.

Both the insert error-rollback loop and arm_smmu_remove_master() then call
rb_erase() on every master->streams[i].node unconditionally. rb_erase() on
a zeroed node sees a NULL parent, treats the node as the tree root and sets
root->rb_node = NULL, silently emptying the whole SID tree and breaking SID
lookups (and DMA) for every other master on the SMMU.

Mark each node with RB_CLEAR_NODE() after sort_nonatomic() reorders the
array, since sorting relocates the entries and would leave the earlier
self-referential RB_CLEAR_NODE() pointer stale. An un-inserted node then
stays RB_EMPTY_NODE() and is skipped in both erase loops; inserted nodes
are linked by rb_find_add() and erased as before.

Fixes: b00d24997a11 ("iommu/arm-smmu-v3: Fix iommu_device_probe bug due to duplicated stream ids")
Assisted-by: LLM
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

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 98f105798b89a..dba6c2942af8f 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4122,6 +4122,13 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 	     sizeof(master->streams[0]), arm_smmu_stream_id_cmp,
 	     NULL);
 
+	/*
+	 * Clear after sorting: RB_CLEAR_NODE() records the node's own address,
+	 * which sort_nonatomic() invalidates by relocating the entries.
+	 */
+	for (i = 0; i < fwspec->num_ids; i++)
+		RB_CLEAR_NODE(&master->streams[i].node);
+
 	mutex_lock(&smmu->streams_mutex);
 	for (i = 0; i < fwspec->num_ids; i++) {
 		struct arm_smmu_stream *new_stream = &master->streams[i];
@@ -4154,7 +4161,9 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 
 	if (ret) {
 		for (i--; i >= 0; i--)
-			rb_erase(&master->streams[i].node, &smmu->streams);
+			if (!RB_EMPTY_NODE(&master->streams[i].node))
+				rb_erase(&master->streams[i].node,
+					 &smmu->streams);
 		kfree(master->streams);
 		kfree(master->build_invs);
 	}
@@ -4174,7 +4183,8 @@ static void arm_smmu_remove_master(struct arm_smmu_master *master)
 
 	mutex_lock(&smmu->streams_mutex);
 	for (i = 0; i < fwspec->num_ids; i++)
-		rb_erase(&master->streams[i].node, &smmu->streams);
+		if (!RB_EMPTY_NODE(&master->streams[i].node))
+			rb_erase(&master->streams[i].node, &smmu->streams);
 	mutex_unlock(&smmu->streams_mutex);
 
 	kfree(master->streams);

-- 
2.34.1