linux-kernel - [PATCH v2 1/2] iommu: Use mutex instead of spinlock for iommu_device

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Date: Fri, 26 Jan 2024 18:53:40 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>,
	Kevin Tian <kevin.tian@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>
Cc: iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH v2 1/2] iommu: Use mutex instead of spinlock for iommu_device_list

The iommu_device_lock spinlock was used to protect the iommu device
list. However, there is no requirement to access the iommu device
list in interrupt context. Therefore, a mutex is sufficient.

This also prepares for the next change, which will iterate the iommu
device list and call the probe callback within the locking area.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/iommu.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 68e648b55767..0af0b5544072 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -146,7 +146,7 @@ struct iommu_group_attribute iommu_group_attr_##_name =		\
 	container_of(_kobj, struct iommu_group, kobj)
 
 static LIST_HEAD(iommu_device_list);
-static DEFINE_SPINLOCK(iommu_device_lock);
+static DEFINE_MUTEX(iommu_device_lock);
 
 static const struct bus_type * const iommu_buses[] = {
 	&platform_bus_type,
@@ -262,9 +262,9 @@ int iommu_device_register(struct iommu_device *iommu,
 	if (hwdev)
 		iommu->fwnode = dev_fwnode(hwdev);
 
-	spin_lock(&iommu_device_lock);
+	mutex_lock(&iommu_device_lock);
 	list_add_tail(&iommu->list, &iommu_device_list);
-	spin_unlock(&iommu_device_lock);
+	mutex_unlock(&iommu_device_lock);
 
 	for (int i = 0; i < ARRAY_SIZE(iommu_buses) && !err; i++)
 		err = bus_iommu_probe(iommu_buses[i]);
@@ -279,9 +279,9 @@ void iommu_device_unregister(struct iommu_device *iommu)
 	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++)
 		bus_for_each_dev(iommu_buses[i], NULL, iommu, remove_iommu_group);
 
-	spin_lock(&iommu_device_lock);
+	mutex_lock(&iommu_device_lock);
 	list_del(&iommu->list);
-	spin_unlock(&iommu_device_lock);
+	mutex_unlock(&iommu_device_lock);
 
 	/* Pairs with the alloc in generic_single_device_group() */
 	iommu_group_put(iommu->singleton_group);
@@ -316,9 +316,9 @@ int iommu_device_register_bus(struct iommu_device *iommu,
 	if (err)
 		return err;
 
-	spin_lock(&iommu_device_lock);
+	mutex_lock(&iommu_device_lock);
 	list_add_tail(&iommu->list, &iommu_device_list);
-	spin_unlock(&iommu_device_lock);
+	mutex_unlock(&iommu_device_lock);
 
 	err = bus_iommu_probe(bus);
 	if (err) {
@@ -2033,9 +2033,9 @@ bool iommu_present(const struct bus_type *bus)
 
 	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++) {
 		if (iommu_buses[i] == bus) {
-			spin_lock(&iommu_device_lock);
+			mutex_lock(&iommu_device_lock);
 			ret = !list_empty(&iommu_device_list);
-			spin_unlock(&iommu_device_lock);
+			mutex_unlock(&iommu_device_lock);
 		}
 	}
 	return ret;
@@ -2983,13 +2983,13 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
 	const struct iommu_ops *ops = NULL;
 	struct iommu_device *iommu;
 
-	spin_lock(&iommu_device_lock);
+	mutex_lock(&iommu_device_lock);
 	list_for_each_entry(iommu, &iommu_device_list, list)
 		if (iommu->fwnode == fwnode) {
 			ops = iommu->ops;
 			break;
 		}
-	spin_unlock(&iommu_device_lock);
+	mutex_unlock(&iommu_device_lock);
 	return ops;
 }
 
-- 
2.34.1