From b66621ad2a8fb553c4cb75b9d69fead4f0532933 Mon Sep 17 00:00:00 2001 From: Daniel Lezcano Date: Tue, 20 Oct 2026 16:45:25 +0200 Subject: [PATCH] ACPI: platform_profile: Separate handler locking from sysfs lifetime MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Registration and removal currently hold profile_lock across device_unregister() and sysfs_update_group(). These operations can remove sysfs attributes and wait for their active callbacks to finish. The profile read and write callbacks acquire profile_lock themselves, so a concurrent access can deadlock: Removal/update path Active sysfs callback ------------------- --------------------- acquire profile_lock hold kernfs active reference remove a sysfs attribute wait for profile_lock wait for its active references The removal path cannot finish until the callback returns, and the callback cannot return until the removal path releases profile_lock. This applies both to per-provider device teardown and to updates of the legacy aggregate attribute group. Commit 041142d7d252 ("ACPI: platform-profile: Fix possible deadlock in platform_profile_remove()") previously fixed this lock ordering by moving sysfs_remove_group() outside profile_lock. Commit 55b1e68134bf ("ACPI: platform_profile: Use guard(mutex) for register/unregister") reintroduced the issue by extending the mutex guard over sysfs_remove_group(). Later, commit 77be5cacb2c2 ("ACPI: platform_profile: Create class for ACPI platform profile") replaced that teardown with device_unregister() and sysfs_update_group(), still under the same mutex, extending the problem to class-device teardown and aggregate attribute updates. Simply dropping profile_lock around these operations is insufficient. Aggregate operations currently discover providers through the class device list. A provider being unregistered could therefore still be selected for an aggregate read, write or cycle while its sysfs files are being torn down. Concurrent registrations and removals would also race when updating aggregate attribute visibility. Introduce profile_registration_lock to serialize registration, removal and aggregate sysfs updates. Sysfs callbacks never acquire this mutex. Retain profile_lock for profile operations and use it to protect an explicit list of handlers participating in the aggregate interface. Add a handler to that list only after device_register() succeeds. On removal, unlink it under profile_lock before calling device_unregister(). Acquiring profile_lock first waits for any aggregate operation already using the handler to complete; unlinking prevents later aggregate operations from finding it. Release profile_lock before draining sysfs callbacks, allowing active per-provider callbacks to complete before the device is released. Apply the same unlink-before-unregister ordering to registration error cleanup. Walk this list for aggregate reads, writes and profile cycling, and use its emptiness to determine aggregate attribute visibility. The class devices remain the per-provider userspace interface. There can now be an interval between removing the last handler from the list and removing the aggregate attributes. Explicitly reject choices reads and writes during that interval: the intersection bitmap starts with every bit set, so an empty traversal must not advertise all profiles or report a successful write without updating a provider. This separates aggregate membership from class device teardown while preserving the existing class and ACPI sysfs interfaces. Fixes: 55b1e68134bf ("ACPI: platform_profile: Use guard(mutex) for register/unregister") Fixes: 77be5cacb2c2 ("ACPI: platform_profile: Create class for ACPI platform profile") Signed-off-by: Daniel Lezcano Reviewed-by: Ilpo Järvinen Reviewed-by: Mark Pearson [ rjw: Subject adjustment, added two empty code lines ] [ rjw: Renamed profile_walk_handlers() to profile_for_each_handler() ] Link: https://patch.msgid.link/20261020144525.3265851-1-daniel.lezcano@oss.qualcomm.com Signed-off-by: Rafael J. Wysocki --- drivers/acpi/platform_profile.c | 82 ++++++++++++++++++++------------- 1 file changed, 49 insertions(+), 33 deletions(-) diff --git a/drivers/acpi/platform_profile.c b/drivers/acpi/platform_profile.c index 79d2e92e5c28..b4c91d57f3d4 100644 --- a/drivers/acpi/platform_profile.c +++ b/drivers/acpi/platform_profile.c @@ -8,15 +8,25 @@ #include #include #include +#include #include #include #include #define to_pprof_handler(d) (container_of(d, struct platform_profile_handler, dev)) +/* + * Protects profile_handlers membership and serializes profile operations + * against each other and handler removal. Never held across sysfs teardown, + * which can wait for callbacks that acquire this lock. + */ static DEFINE_MUTEX(profile_lock); +/* Serialize registration and sysfs updates without blocking sysfs callbacks. */ +static DEFINE_MUTEX(profile_registration_lock); +static LIST_HEAD(profile_handlers); struct platform_profile_handler { + struct list_head node; const char *name; struct device dev; int minor; @@ -44,6 +54,23 @@ static_assert(ARRAY_SIZE(profile_names) == PLATFORM_PROFILE_LAST); static DEFINE_IDA(platform_profile_ida); +static int profile_for_each_handler(void *data, + int (*fn)(struct device *dev, void *data)) +{ + struct platform_profile_handler *handler; + int ret; + + lockdep_assert_held(&profile_lock); + + list_for_each_entry(handler, &profile_handlers, node) { + ret = fn(&handler->dev, data); + if (ret) + return ret; + } + + return 0; +} + /** * _commmon_choices_show - Show the available profile choices * @choices: The available profile choices @@ -306,20 +333,18 @@ static ssize_t platform_profile_choices_show(struct kobject *kobj, int err; scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) { - err = class_for_each_device(&platform_profile_class, NULL, - &data, _aggregate_choices); + err = profile_for_each_handler(&data, _aggregate_choices); if (err) return err; if (data.count == 1) { - err = class_for_each_device(&platform_profile_class, NULL, - &data, _remove_hidden_choices); + err = profile_for_each_handler(&data, _remove_hidden_choices); if (err) return err; } } /* no profile handler registered any more */ - if (bitmap_empty(data.aggregate, PLATFORM_PROFILE_LAST)) + if (!data.count || bitmap_empty(data.aggregate, PLATFORM_PROFILE_LAST)) return -EINVAL; return _commmon_choices_show(data.aggregate, buf); @@ -384,8 +409,7 @@ static ssize_t platform_profile_show(struct kobject *kobj, int err; scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) { - err = class_for_each_device(&platform_profile_class, NULL, - &profile, _aggregate_profiles); + err = profile_for_each_handler(&profile, _aggregate_profiles); if (err) return err; } @@ -423,15 +447,13 @@ static ssize_t platform_profile_store(struct kobject *kobj, return -EINVAL; scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) { - ret = class_for_each_device(&platform_profile_class, NULL, - &data, _aggregate_choices); + ret = profile_for_each_handler(&data, _aggregate_choices); if (ret) return ret; - if (!test_bit(i, data.aggregate)) + if (!data.count || !test_bit(i, data.aggregate)) return -EOPNOTSUPP; - ret = class_for_each_device(&platform_profile_class, NULL, &i, - _store_and_notify); + ret = profile_for_each_handler(&i, _store_and_notify); if (ret) return ret; } @@ -450,22 +472,11 @@ static struct attribute *platform_profile_attrs[] = { NULL }; -static int profile_class_registered(struct device *dev, const void *data) -{ - return 1; -} - static umode_t profile_class_is_visible(struct kobject *kobj, struct attribute *attr, int idx) { - struct device *dev; + guard(mutex)(&profile_lock); - dev = class_find_device(&platform_profile_class, NULL, NULL, profile_class_registered); - if (!dev) - return 0; - - put_device(dev); - - return attr->mode; + return list_empty(&profile_handlers) ? 0 : attr->mode; } static const struct attribute_group platform_profile_group = { @@ -502,8 +513,7 @@ int platform_profile_cycle(void) int err; scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) { - err = class_for_each_device(&platform_profile_class, NULL, - &profile, _aggregate_profiles); + err = profile_for_each_handler(&profile, _aggregate_profiles); if (err) return err; @@ -512,8 +522,7 @@ int platform_profile_cycle(void) profile == PLATFORM_PROFILE_LAST) return -EINVAL; - err = class_for_each_device(&platform_profile_class, NULL, - &data, _aggregate_choices); + err = profile_for_each_handler(&data, _aggregate_choices); if (err) return err; @@ -525,8 +534,7 @@ int platform_profile_cycle(void) PLATFORM_PROFILE_LAST, profile + 1); - err = class_for_each_device(&platform_profile_class, NULL, &next, - _store_and_notify); + err = profile_for_each_handler(&next, _store_and_notify); if (err) return err; @@ -583,7 +591,7 @@ struct device *platform_profile_register(struct device *dev, const char *name, } } - guard(mutex)(&profile_lock); + guard(mutex)(&profile_registration_lock); /* create class interface for individual handler */ minor = ida_alloc(&platform_profile_ida, GFP_KERNEL); @@ -604,6 +612,8 @@ struct device *platform_profile_register(struct device *dev, const char *name, put_device(ppdev); goto cleanup_ida; } + scoped_guard(mutex, &profile_lock) + list_add_tail(&to_pprof_handler(ppdev)->node, &profile_handlers); sysfs_notify(acpi_kobj, NULL, "platform_profile"); @@ -614,6 +624,9 @@ struct device *platform_profile_register(struct device *dev, const char *name, return ppdev; cleanup_cur: + scoped_guard(mutex, &profile_lock) + list_del(&to_pprof_handler(ppdev)->node); + device_unregister(ppdev); cleanup_ida: @@ -636,7 +649,10 @@ void platform_profile_remove(struct device *dev) pprof = to_pprof_handler(dev); - guard(mutex)(&profile_lock); + guard(mutex)(&profile_registration_lock); + + scoped_guard(mutex, &profile_lock) + list_del(&pprof->node); ida_free(&platform_profile_ida, pprof->minor); device_unregister(&pprof->dev);