[PATCH 04/11] iommu: Simplify the __iommu_group_remove_device() flow

Jason Gunthorpe
2023-04-19T16:12:46Z

Instead of returning the struct group_device and then later freeing it, do
the entire free under the group->mutex and defer only putting the
iommu_group.

It is safe to remove the sysfs_links and free memory while holding that
mutex.

Move the sanity assert of the group status into
__iommu_group_free_device().

The next patch will improve upon this and consolidate the group put and
the mutex into __iommu_group_remove_device().

__iommu_group_free_device() is close to being the paired undo of
iommu_group_add_device(), following patches will improve on that.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/iommu.c | 83 ++++++++++++++++++++-----------------------
1 file changed, 39 insertions(+), 44 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index e08856c17121d8..471f19f7de8c4a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -466,32 +466,8 @@ int iommu_probe_device(struct device *dev)

}

-/*
- * Remove a device from a group's device list and return the group device
- * if successful.
- */
-static struct group_device *
-__iommu_group_remove_device(struct iommu_group *group, struct device *dev)
-{
- struct group_device *device;
-
- lockdep_assert_held(&group->mutex);
- for_each_group_device(group, device) {
- if (device->dev == dev) {
- list_del(&device->list);
- return device;
- }
- }
-
- return NULL;
-}
-
-/*
- * Release a device from its group and decrements the iommu group reference
- * count.
- */
-static void __iommu_group_release_device(struct iommu_group *group,
- struct group_device *grp_dev)
+static void __iommu_group_free_device(struct iommu_group *group,
+ struct group_device *grp_dev)
{
struct device *dev = grp_dev->dev;

@@ -500,16 +476,45 @@ static void __iommu_group_release_device(struct iommu_group *group,

trace_remove_device_from_group(group->id, dev);

+ /*
+ * If the group has become empty then ownership must have been
+ * released, and the current domain must be set back to NULL or
+ * the default domain.
+ */
+ if (list_empty(&group->devices))
+ WARN_ON(group->owner_cnt ||
+ group->domain != group->default_domain);
+
kfree(grp_dev->name);
kfree(grp_dev);
dev->iommu_group = NULL;
- iommu_group_put(group);
}

-static void iommu_release_device(struct device *dev)
+/*
+ * Remove the iommu_group from the struct device. The attached group must be put
+ * by the caller after releaseing the group->mutex.
+ */
+static void __iommu_group_remove_device(struct device *dev)
{
struct iommu_group *group = dev->iommu_group;
struct group_device *device;
+
+ lockdep_assert_held(&group->mutex);
+ for_each_group_device(group, device) {
+ if (device->dev != dev)
+ continue;
+
+ list_del(&device->list);
+ __iommu_group_free_device(group, device);
+ /* Caller must put iommu_group */
+ return;
+ }
+ WARN(true, "Corrupted iommu_group device_list");
+}
+
+static void iommu_release_device(struct device *dev)
+{
+ struct iommu_group *group = dev->iommu_group;
const struct iommu_ops *ops;

if (!dev->iommu || !group)
@@ -518,16 +523,7 @@ static void iommu_release_device(struct device *dev)
iommu_device_unlink(dev->iommu->iommu_dev, dev);

mutex_lock(&group->mutex);
- device = __iommu_group_remove_device(group, dev);
-
- /*
- * If the group has become empty then ownership must have been released,
- * and the current domain must be set back to NULL or the default
- * domain.
- */
- if (list_empty(&group->devices))
- WARN_ON(group->owner_cnt ||
- group->domain != group->default_domain);
+ __iommu_group_remove_device(dev);

/*
* release_device() must stop using any attached domain on the device.
@@ -543,8 +539,8 @@ static void iommu_release_device(struct device *dev)
ops->release_device(dev);
mutex_unlock(&group->mutex);

- if (device)
- __iommu_group_release_device(group, device);
+ /* Pairs with the get in iommu_group_add_device() */
+ iommu_group_put(group);

module_put(ops->owner);
dev_iommu_free(dev);
@@ -1103,7 +1099,6 @@ EXPORT_SYMBOL_GPL(iommu_group_add_device);
void iommu_group_remove_device(struct device *dev)
{
struct iommu_group *group = dev->iommu_group;
- struct group_device *device;

if (!group)
return;
@@ -1111,11 +1106,11 @@ void iommu_group_remove_device(struct device *dev)
dev_info(dev, "Removing from iommu group %d\n", group->id);

mutex_lock(&group->mutex);
- device = __iommu_group_remove_device(group, dev);
+ __iommu_group_remove_device(dev);
mutex_unlock(&group->mutex);

- if (device)
- __iommu_group_release_device(group, device);
+ /* Pairs with the get in iommu_group_add_device() */
+ iommu_group_put(group);
}
EXPORT_SYMBOL_GPL(iommu_group_remove_device);

--
2.40.0