[PATCH 6.18 010/309] driver core: generalize driver_override in struct device

Greg Kroah-Hartman
2026-03-31T16:57:02Z

From: Danilo Krummrich <dakr@kernel.org>

[ Upstream commit cb3d1049f4ea77d5ad93f17d8ac1f2ed4da70501 ]

Currently, there are 12 busses (including platform and PCI) that
duplicate the driver_override logic for their individual devices.

All of them seem to be prone to the bug described in [1].

While this could be solved for every bus individually using a separate
lock, solving this in the driver-core generically results in less (and
cleaner) changes overall.

Thus, move driver_override to struct device, provide corresponding
accessors for busses and handle locking with a separate lock internally.

In particular, add device_set_driver_override(),
device_has_driver_override(), device_match_driver_override() and
generalize the sysfs store() and show() callbacks via a driver_override
feature flag in struct bus_type.

Until all busses have migrated, keep driver_set_override() in place.

Note that we can't use the device lock for the reasons described in [2].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=220789 [1]
Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [2]
Tested-by: Gui-Dong Han <hanguidong02@gmail.com>
Co-developed-by: Gui-Dong Han <hanguidong02@gmail.com>
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260303115720.48783-2-dakr@kernel.org
[ Use dev->bus instead of sp->bus for consistency; fix commit message to
refer to the struct bus_type's driver_override feature flag. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Stable-dep-of: 2b38efc05bf7 ("driver core: platform: use generic driver_override infrastructure")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/base/bus.c | 43 ++++++++++++++++++++++++++-
drivers/base/core.c | 2 ++
drivers/base/dd.c | 60 ++++++++++++++++++++++++++++++++++++++
include/linux/device.h | 54 ++++++++++++++++++++++++++++++++++
include/linux/device/bus.h | 4 +++
5 files changed, 162 insertions(+), 1 deletion(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 5e75e1bce5516..2653670f962f4 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -466,6 +466,36 @@ int bus_for_each_drv(const struct bus_type *bus, struct device_driver *start,
}
EXPORT_SYMBOL_GPL(bus_for_each_drv);

+static ssize_t driver_override_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ int ret;
+
+ ret = __device_set_driver_override(dev, buf, count);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ guard(spinlock)(&dev->driver_override.lock);
+ return sysfs_emit(buf, "%s\n", dev->driver_override.name);
+}
+static DEVICE_ATTR_RW(driver_override);
+
+static struct attribute *driver_override_dev_attrs[] = {
+ &dev_attr_driver_override.attr,
+ NULL,
+};
+
+static const struct attribute_group driver_override_dev_group = {
+ .attrs = driver_override_dev_attrs,
+};
+
/**
* bus_add_device - add device to bus
* @dev: device being added
@@ -499,9 +529,15 @@ int bus_add_device(struct device *dev)
if (error)
goto out_put;

+ if (dev->bus->driver_override) {
+ error = device_add_group(dev, &driver_override_dev_group);
+ if (error)
+ goto out_groups;
+ }
+
error = sysfs_create_link(&sp->devices_kset->kobj, &dev->kobj, dev_name(dev));
if (error)
- goto out_groups;
+ goto out_override;

error = sysfs_create_link(&dev->kobj, &sp->subsys.kobj, "subsystem");
if (error)
@@ -512,6 +548,9 @@ int bus_add_device(struct device *dev)

out_subsys:
sysfs_remove_link(&sp->devices_kset->kobj, dev_name(dev));
+out_override:
+ if (dev->bus->driver_override)
+ device_remove_group(dev, &driver_override_dev_group);
out_groups:
device_remove_groups(dev, sp->bus->dev_groups);
out_put:
@@ -570,6 +609,8 @@ void bus_remove_device(struct device *dev)

sysfs_remove_link(&dev->kobj, "subsystem");
sysfs_remove_link(&sp->devices_kset->kobj, dev_name(dev));
+ if (dev->bus->driver_override)
+ device_remove_group(dev, &driver_override_dev_group);
device_remove_groups(dev, dev->bus->dev_groups);
if (klist_node_attached(&dev->p->knode_bus))
klist_del(&dev->p->knode_bus);
diff --git a/drivers/base/core.c b/drivers/base/core.c
index f69dc9c859545..3099dbca234ab 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2556,6 +2556,7 @@ static void device_release(struct kobject *kobj)
devres_release_all(dev);

kfree(dev->dma_range_map);
+ kfree(dev->driver_override.name);

if (dev->release)
dev->release(dev);
@@ -3159,6 +3160,7 @@ void device_initialize(struct device *dev)
kobject_init(&dev->kobj, &device_ktype);
INIT_LIST_HEAD(&dev->dma_pools);
mutex_init(&dev->mutex);
+ spin_lock_init(&dev->driver_override.lock);
lockdep_set_novalidate_class(&dev->mutex);
spin_lock_init(&dev->devres_lock);
INIT_LIST_HEAD(&dev->devres_head);
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 13ab98e033eaa..2996f4c667c42 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -381,6 +381,66 @@ static void __exit deferred_probe_exit(void)
}
__exitcall(deferred_probe_exit);

+int __device_set_driver_override(struct device *dev, const char *s, size_t len)
+{
+ const char *new, *old;
+ char *cp;
+
+ if (!s)
+ return -EINVAL;
+
+ /*
+ * The stored value will be used in sysfs show callback (sysfs_emit()),
+ * which has a length limit of PAGE_SIZE and adds a trailing newline.
+ * Thus we can store one character less to avoid truncation during sysfs
+ * show.
+ */
+ if (len >= (PAGE_SIZE - 1))
+ return -EINVAL;
+
+ /*
+ * Compute the real length of the string in case userspace sends us a
+ * bunch of \0 characters like python likes to do.
+ */
+ len = strlen(s);
+
+ if (!len) {
+ /* Empty string passed - clear override */
+ spin_lock(&dev->driver_override.lock);
+ old = dev->driver_override.name;
+ dev->driver_override.name = NULL;
+ spin_unlock(&dev->driver_override.lock);
+ kfree(old);
+
+ return 0;
+ }
+
+ cp = strnchr(s, len, '\n');
+ if (cp)
+ len = cp - s;
+
+ new = kstrndup(s, len, GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+
+ spin_lock(&dev->driver_override.lock);
+ old = dev->driver_override.name;
+ if (cp != s) {
+ dev->driver_override.name = new;
+ spin_unlock(&dev->driver_override.lock);
+ } else {
+ /* "\n" passed - clear override */
+ dev->driver_override.name = NULL;
+ spin_unlock(&dev->driver_override.lock);
+
+ kfree(new);
+ }
+ kfree(old);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(__device_set_driver_override);
+
/**
* device_is_bound() - Check if device is bound to a driver
* @dev: device to check
diff --git a/include/linux/device.h b/include/linux/device.h
index b031ff71a5bdf..8733a4edf3ccd 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -502,6 +502,8 @@ struct device_physical_location {
* on. This shrinks the "Board Support Packages" (BSPs) and
* minimizes board-specific #ifdefs in drivers.
* @driver_data: Private pointer for driver specific info.
+ * @driver_override: Driver name to force a match. Do not touch directly; use
+ * device_set_driver_override() instead.
* @links: Links to suppliers and consumers of this device.
* @power: For device power management.
* See Documentation/driver-api/pm/devices.rst for details.
@@ -595,6 +597,10 @@ struct device {
core doesn't touch it */
void *driver_data; /* Driver data, set and get with
dev_set_drvdata/dev_get_drvdata */
+ struct {
+ const char *name;
+ spinlock_t lock;
+ } driver_override;
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
@@ -720,6 +726,54 @@ struct device_link {

#define kobj_to_dev(__kobj) container_of_const(__kobj, struct device, kobj)

+int __device_set_driver_override(struct device *dev, const char *s, size_t len);
+
+/**
+ * device_set_driver_override() - Helper to set or clear driver override.
+ * @dev: Device to change
+ * @s: NUL-terminated string, new driver name to force a match, pass empty
+ * string to clear it ("" or "\n", where the latter is only for sysfs
+ * interface).
+ *
+ * Helper to set or clear driver override of a device.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int device_set_driver_override(struct device *dev, const char *s)
+{
+ return __device_set_driver_override(dev, s, s ? strlen(s) : 0);
+}
+
+/**
+ * device_has_driver_override() - Check if a driver override has been set.
+ * @dev: device to check
+ *
+ * Returns true if a driver override has been set for this device.
+ */
+static inline bool device_has_driver_override(struct device *dev)
+{
+ guard(spinlock)(&dev->driver_override.lock);
+ return !!dev->driver_override.name;
+}
+
+/**
+ * device_match_driver_override() - Match a driver against the device's driver_override.
+ * @dev: device to check
+ * @drv: driver to match against
+ *
+ * Returns > 0 if a driver override is set and matches the given driver, 0 if a
+ * driver override is set but does not match, or < 0 if a driver override is not
+ * set at all.
+ */
+static inline int device_match_driver_override(struct device *dev,
+ const struct device_driver *drv)
+{
+ guard(spinlock)(&dev->driver_override.lock);
+ if (dev->driver_override.name)
+ return !strcmp(dev->driver_override.name, drv->name);
+ return -1;
+}
+
/**
* device_iommu_mapped - Returns true when the device DMA is translated
* by an IOMMU
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index f5a56efd2bd6a..15de0d7881f9e 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -63,6 +63,9 @@ struct fwnode_handle;
* this bus.
* @pm: Power management operations of this bus, callback the specific
* device driver's pm-ops.
+ * @driver_override: Set to true if this bus supports the driver_override
+ * mechanism, which allows userspace to force a specific
+ * driver to bind to a device via a sysfs attribute.
* @need_parent_lock: When probing or removing a device on this bus, the
* device core should lock the device's parent.
*
@@ -104,6 +107,7 @@ struct bus_type {

const struct dev_pm_ops *pm;

+ bool driver_override;
bool need_parent_lock;
};

--
2.51.0