[PATCH v2 4/6] iommu: Move lock from iommu_change_dev_def_domain() to its caller

From: Lu Baolu
Date: Fri Feb 17 2023 - 04:56:36 EST


The intention is to make it possible to put group ownership check and
default domain change in a same critical region protected by the group's
mutex lock. No intentional functional change.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
drivers/iommu/iommu.c | 29 ++++++++++++++---------------
1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 093692308b80..e1ae1eb4faf0 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2892,7 +2892,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
int ret, dev_def_dom;
struct device *dev;

- mutex_lock(&group->mutex);
+ lockdep_assert_held(&group->mutex);

if (group->default_domain != group->domain) {
dev_err_ratelimited(prev_dev, "Group not assigned to default domain\n");
@@ -2980,28 +2980,15 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
goto free_new_domain;

group->domain = group->default_domain;
-
- /*
- * Release the mutex here because ops->probe_finalize() call-back of
- * some vendor IOMMU drivers calls arm_iommu_attach_device() which
- * in-turn might call back into IOMMU core code, where it tries to take
- * group->mutex, resulting in a deadlock.
- */
- mutex_unlock(&group->mutex);
-
- /* Make sure dma_ops is appropriatley set */
- iommu_group_do_probe_finalize(dev, group->default_domain);
iommu_domain_free(prev_dom);
+
return 0;

free_new_domain:
iommu_domain_free(group->default_domain);
group->default_domain = prev_dom;
group->domain = prev_dom;
-
out:
- mutex_unlock(&group->mutex);
-
return ret;
}

@@ -3089,7 +3076,19 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
goto out;
}

+ mutex_lock(&group->mutex);
ret = iommu_change_dev_def_domain(group, dev, req_type);
+ /*
+ * Release the mutex here because ops->probe_finalize() call-back of
+ * some vendor IOMMU drivers calls arm_iommu_attach_device() which
+ * in-turn might call back into IOMMU core code, where it tries to take
+ * group->mutex, resulting in a deadlock.
+ */
+ mutex_unlock(&group->mutex);
+
+ /* Make sure dma_ops is appropriatley set */
+ if (!ret)
+ iommu_group_do_probe_finalize(dev, group->default_domain);
ret = ret ?: count;

out:
--
2.34.1