Driver core fixes for 6.15-rc4

Here are some small driver core fixes to resolve a number of reported
 problems.  Included in here are:
   - driver core sync fix revert to resolve a much reported problem,
     hopefully this is finally resolved
   - MAINTAINERS file update, documenting that the driver-core tree is
     now under a "shared" maintainership model, thanks to Rafael and
     Danilo for offering to do this!
   - auxbus documentation and MAINTAINERS file update
   - MAINTAINERS file update for Rust PCI code
   - firmware rust binding fixup
   - software node link fix
 
 All of these have been in linux-next for over a week with no reported
 issues.
 
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Merge tag 'driver-core-6.15-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core

Pull driver core fixes from Greg KH:
 "Here are some small driver core fixes to resolve a number of reported
  problems. Included in here are:

   - driver core sync fix revert to resolve a much reported problem,
     hopefully this is finally resolved

   - MAINTAINERS file update, documenting that the driver-core tree is
     now under a "shared" maintainership model, thanks to Rafael and
     Danilo for offering to do this!

   - auxbus documentation and MAINTAINERS file update

   - MAINTAINERS file update for Rust PCI code

   - firmware rust binding fixup

   - software node link fix

  All of these have been in linux-next for over a week with no reported
  issues"

* tag 'driver-core-6.15-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core:
  drivers/base/memory: Avoid overhead from for_each_present_section_nr()
  software node: Prevent link creation failure from causing kobj reference count imbalance
  device property: Add a note to the fwnode.h
  drivers/base: Add myself as auxiliary bus reviewer
  drivers/base: Extend documentation with preferred way to use auxbus
  driver core: fix potential NULL pointer dereference in dev_uevent()
  driver core: introduce device_set_driver() helper
  Revert "drivers: core: synchronize really_probe() and dev_uevent()"
  MAINTAINERS: update the location of the driver-core git tree
  rust: firmware: Use `ffi::c_char` type in `FwFunc`
  MAINTAINERS: pci: add entry for Rust PCI code

MAINTAINERS

@@ -3873,8 +3873,9 @@ AUXILIARY BUS DRIVER
 M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 R:	Dave Ertman <david.m.ertman@intel.com>
 R:	Ira Weiny <ira.weiny@intel.com>
+R:	Leon Romanovsky <leon@kernel.org>
 S:	Supported
-T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core.git
 F:	Documentation/driver-api/auxiliary_bus.rst
 F:	drivers/base/auxiliary.c
 F:	include/linux/auxiliary_bus.h
@@ -7233,7 +7234,7 @@ M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 M:	"Rafael J. Wysocki" <rafael@kernel.org>
 M:	Danilo Krummrich <dakr@kernel.org>
 S:	Supported
-T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core.git
 F:	Documentation/core-api/kobject.rst
 F:	drivers/base/
 F:	fs/debugfs/
@@ -13118,7 +13119,7 @@ KERNFS
 M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 M:	Tejun Heo <tj@kernel.org>
 S:	Supported
-T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core.git
 F:	fs/kernfs/
 F:	include/linux/kernfs.h
 
@@ -18750,6 +18751,16 @@ F:	include/asm-generic/pci*
 F:	include/linux/of_pci.h
 F:	include/linux/pci*
 F:	include/uapi/linux/pci*
+
+PCI SUBSYSTEM [RUST]
+M:	Danilo Krummrich <dakr@kernel.org>
+R:	Bjorn Helgaas <bhelgaas@google.com>
+R:	Krzysztof Wilczyński <kwilczynski@kernel.org>
+L:	linux-pci@vger.kernel.org
+S:	Maintained
+C:	irc://irc.oftc.net/linux-pci
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git
+F:	rust/helpers/pci.c
 F:	rust/kernel/pci.rs
 F:	samples/rust/rust_driver_pci.rs
 

drivers/base/auxiliary.c

@@ -156,6 +156,16 @@
  *		},
  *		.ops = my_custom_ops,
  *	};
+ *
+ * Please note that such custom ops approach is valid, but it is hard to implement
+ * it right without global locks per-device to protect from auxiliary_drv removal
+ * during call to that ops. In addition, this implementation lacks proper module
+ * dependency, which causes to load/unload races between auxiliary parent and devices
+ * modules.
+ *
+ * The most easiest way to provide these ops reliably without needing to
+ * have a lock is to EXPORT_SYMBOL*() them and rely on already existing
+ * modules infrastructure for validity and correct dependencies chains.
  */
 
 static const struct auxiliary_device_id *auxiliary_match_id(const struct auxiliary_device_id *id,

drivers/base/base.h

@@ -73,6 +73,7 @@ static inline void subsys_put(struct subsys_private *sp)
 		kset_put(&sp->subsys);
 }
 
+struct subsys_private *bus_to_subsys(const struct bus_type *bus);
 struct subsys_private *class_to_subsys(const struct class *class);
 
 struct driver_private {
@@ -180,6 +181,22 @@ int driver_add_groups(const struct device_driver *drv, const struct attribute_gr
 void driver_remove_groups(const struct device_driver *drv, const struct attribute_group **groups);
 void device_driver_detach(struct device *dev);
 
+static inline void device_set_driver(struct device *dev, const struct device_driver *drv)
+{
+	/*
+	 * Majority (all?) read accesses to dev->driver happens either
+	 * while holding device lock or in bus/driver code that is only
+	 * invoked when the device is bound to a driver and there is no
+	 * concern of the pointer being changed while it is being read.
+	 * However when reading device's uevent file we read driver pointer
+	 * without taking device lock (so we do not block there for
+	 * arbitrary amount of time). We use WRITE_ONCE() here to prevent
+	 * tearing so that READ_ONCE() can safely be used in uevent code.
+	 */
+	// FIXME - this cast should not be needed "soon"
+	WRITE_ONCE(dev->driver, (struct device_driver *)drv);
+}
+
 int devres_release_all(struct device *dev);
 void device_block_probing(void);
 void device_unblock_probing(void);

drivers/base/bus.c

@@ -57,7 +57,7 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
  * NULL.  A call to subsys_put() must be done when finished with the pointer in
  * order for it to be properly freed.
  */
-static struct subsys_private *bus_to_subsys(const struct bus_type *bus)
+struct subsys_private *bus_to_subsys(const struct bus_type *bus)
 {
 	struct subsys_private *sp = NULL;
 	struct kobject *kobj;

drivers/base/core.c

@@ -2624,6 +2624,35 @@ static const char *dev_uevent_name(const struct kobject *kobj)
 	return NULL;
 }
 
+/*
+ * Try filling "DRIVER=<name>" uevent variable for a device. Because this
+ * function may race with binding and unbinding the device from a driver,
+ * we need to be careful. Binding is generally safe, at worst we miss the
+ * fact that the device is already bound to a driver (but the driver
+ * information that is delivered through uevents is best-effort, it may
+ * become obsolete as soon as it is generated anyways). Unbinding is more
+ * risky as driver pointer is transitioning to NULL, so READ_ONCE() should
+ * be used to make sure we are dealing with the same pointer, and to
+ * ensure that driver structure is not going to disappear from under us
+ * we take bus' drivers klist lock. The assumption that only registered
+ * driver can be bound to a device, and to unregister a driver bus code
+ * will take the same lock.
+ */
+static void dev_driver_uevent(const struct device *dev, struct kobj_uevent_env *env)
+{
+	struct subsys_private *sp = bus_to_subsys(dev->bus);
+
+	if (sp) {
+		scoped_guard(spinlock, &sp->klist_drivers.k_lock) {
+			struct device_driver *drv = READ_ONCE(dev->driver);
+			if (drv)
+				add_uevent_var(env, "DRIVER=%s", drv->name);
+		}
+
+		subsys_put(sp);
+	}
+}
+
 static int dev_uevent(const struct kobject *kobj, struct kobj_uevent_env *env)
 {
 	const struct device *dev = kobj_to_dev(kobj);
@@ -2655,8 +2684,8 @@ static int dev_uevent(const struct kobject *kobj, struct kobj_uevent_env *env)
 	if (dev->type && dev->type->name)
 		add_uevent_var(env, "DEVTYPE=%s", dev->type->name);
 
-	if (dev->driver)
+	/* Add "DRIVER=%s" variable if the device is bound to a driver */
-		add_uevent_var(env, "DRIVER=%s", dev->driver->name);
+	dev_driver_uevent(dev, env);
 
 	/* Add common DT information about the device */
 	of_device_uevent(dev, env);
@@ -2726,11 +2755,8 @@ static ssize_t uevent_show(struct device *dev, struct device_attribute *attr,
 	if (!env)
 		return -ENOMEM;
 
-	/* Synchronize with really_probe() */
-	device_lock(dev);
 	/* let the kset specific function add its keys */
 	retval = kset->uevent_ops->uevent(&dev->kobj, env);
-	device_unlock(dev);
 	if (retval)
 		goto out;
 
@@ -3700,7 +3726,7 @@ done:
 	device_pm_remove(dev);
 	dpm_sysfs_remove(dev);
  DPMError:
-	dev->driver = NULL;
+	device_set_driver(dev, NULL);
 	bus_remove_device(dev);
  BusError:
 	device_remove_attrs(dev);

drivers/base/dd.c

@@ -550,7 +550,7 @@ static void device_unbind_cleanup(struct device *dev)
 	arch_teardown_dma_ops(dev);
 	kfree(dev->dma_range_map);
 	dev->dma_range_map = NULL;
-	dev->driver = NULL;
+	device_set_driver(dev, NULL);
 	dev_set_drvdata(dev, NULL);
 	if (dev->pm_domain && dev->pm_domain->dismiss)
 		dev->pm_domain->dismiss(dev);
@@ -629,8 +629,7 @@ static int really_probe(struct device *dev, const struct device_driver *drv)
 	}
 
 re_probe:
-	// FIXME - this cast should not be needed "soon"
+	device_set_driver(dev, drv);
-	dev->driver = (struct device_driver *)drv;
 
 	/* If using pinctrl, bind pins now before probing */
 	ret = pinctrl_bind_pins(dev);
@@ -1014,7 +1013,7 @@ static int __device_attach(struct device *dev, bool allow_async)
 		if (ret == 0)
 			ret = 1;
 		else {
-			dev->driver = NULL;
+			device_set_driver(dev, NULL);
 			ret = 0;
 		}
 	} else {

drivers/base/memory.c

@@ -816,21 +816,6 @@ static int add_memory_block(unsigned long block_id, unsigned long state,
 	return 0;
 }
 
-static int __init add_boot_memory_block(unsigned long base_section_nr)
-{
-	unsigned long nr;
-
-	for_each_present_section_nr(base_section_nr, nr) {
-		if (nr >= (base_section_nr + sections_per_block))
-			break;
-
-		return add_memory_block(memory_block_id(base_section_nr),
-					MEM_ONLINE, NULL, NULL);
-	}
-
-	return 0;
-}
-
 static int add_hotplug_memory_block(unsigned long block_id,
 				    struct vmem_altmap *altmap,
 				    struct memory_group *group)
@@ -957,7 +942,7 @@ static const struct attribute_group *memory_root_attr_groups[] = {
 void __init memory_dev_init(void)
 {
 	int ret;
-	unsigned long block_sz, nr;
+	unsigned long block_sz, block_id, nr;
 
 	/* Validate the configured memory block size */
 	block_sz = memory_block_size_bytes();
@@ -970,15 +955,23 @@ void __init memory_dev_init(void)
 		panic("%s() failed to register subsystem: %d\n", __func__, ret);
 
 	/*
-	 * Create entries for memory sections that were found
+	 * Create entries for memory sections that were found during boot
-	 * during boot and have been initialized
+	 * and have been initialized. Use @block_id to track the last
+	 * handled block and initialize it to an invalid value (ULONG_MAX)
+	 * to bypass the block ID matching check for the first present
+	 * block so that it can be covered.
 	 */
-	for (nr = 0; nr <= __highest_present_section_nr;
+	block_id = ULONG_MAX;
-	     nr += sections_per_block) {
+	for_each_present_section_nr(0, nr) {
-		ret = add_boot_memory_block(nr);
+		if (block_id != ULONG_MAX && memory_block_id(nr) == block_id)
-		if (ret)
+			continue;
-			panic("%s() failed to add memory block: %d\n", __func__,
+
-			      ret);
+		block_id = memory_block_id(nr);
+		ret = add_memory_block(block_id, MEM_ONLINE, NULL, NULL);
+		if (ret) {
+			panic("%s() failed to add memory block: %d\n",
+			      __func__, ret);
+		}
 	}
 }
 

drivers/base/swnode.c

@@ -1080,6 +1080,7 @@ void software_node_notify(struct device *dev)
 	if (!swnode)
 		return;
 
+	kobject_get(&swnode->kobj);
 	ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
 	if (ret)
 		return;
@@ -1089,8 +1090,6 @@ void software_node_notify(struct device *dev)
 		sysfs_remove_link(&dev->kobj, "software_node");
 		return;
 	}
-
-	kobject_get(&swnode->kobj);
 }
 
 void software_node_notify_remove(struct device *dev)

include/linux/fwnode.h

@@ -2,6 +2,11 @@
 /*
  * fwnode.h - Firmware device node object handle type definition.
  *
+ * This header file provides low-level data types and definitions for firmware
+ * and device property providers. The respective API header files supplied by
+ * them should contain all of the requisite data types and definitions for end
+ * users, so including it directly should not be necessary.
+ *
  * Copyright (C) 2015, Intel Corporation
  * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
  */

rust/kernel/firmware.rs

@@ -4,7 +4,7 @@
 //!
 //! C header: [`include/linux/firmware.h`](srctree/include/linux/firmware.h)
 
-use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
+use crate::{bindings, device::Device, error::Error, error::Result, ffi, str::CStr};
 use core::ptr::NonNull;
 
 /// # Invariants
@@ -12,7 +12,11 @@ use core::ptr::NonNull;
 /// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
 /// `bindings::firmware_request_platform`, `bindings::request_firmware_direct`.
 struct FwFunc(
-    unsafe extern "C" fn(*mut *const bindings::firmware, *const u8, *mut bindings::device) -> i32,
+    unsafe extern "C" fn(
+        *mut *const bindings::firmware,
+        *const ffi::c_char,
+        *mut bindings::device,
+    ) -> i32,
 );
 
 impl FwFunc {