On 11/18/2024 18:28, Armin Wolf wrote:
Am 18.11.24 um 20:43 schrieb Armin Wolf:
Am 09.11.24 um 05:41 schrieb Mario Limonciello:
The name attribute shows the name of the associated platform profile
handler.
Tested-by: Mark Pearson <mpearson-lenovo@xxxxxxxxx>
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
drivers/acpi/platform_profile.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/drivers/acpi/platform_profile.c
b/drivers/acpi/platform_profile.c
index ef6af2c655524..4e2eda18f7f5f 100644
--- a/drivers/acpi/platform_profile.c
+++ b/drivers/acpi/platform_profile.c
@@ -25,8 +25,35 @@ static_assert(ARRAY_SIZE(profile_names) ==
PLATFORM_PROFILE_LAST);
static DEFINE_IDA(platform_profile_ida);
+/**
+ * name_show - Show the name of the profile handler
+ * @dev: The device
+ * @attr: The attribute
+ * @buf: The buffer to write to
+ * Return: The number of bytes written
+ */
+static ssize_t name_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct platform_profile_handler *handler = dev_get_drvdata(dev);
+
+ scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) {
+ return sysfs_emit(buf, "%s\n", handler->name);
+ }
+ return -ERESTARTSYS;
I still have a bad feeling about the locking inside the class
attributes...
Can we assume that no sysfs accesses occur after unregistering the
class device?
Even if this is not the case then the locking fails to protect the
platform_profile_handler here.
If the device is unregistered right after dev_get_drvdata() was
called, then we would sill operate
on possibly stale data once we take the profile_lock.
Does someone have any clue how sysfs attributes act during removal?
I think i found the answer to my questions inside this patch series:
https://lore.kernel.org/linux-kernel/1390951311-15325-1-git-send-email-
tj@xxxxxxxxxx
It says that:
kernfs / sysfs implement the "sever" semantic for userland accesses.
When a node is removed, no further userland operations are allowed and
the in-flight ones are drained before removal is finished. This makes
policing post-mortem userland accesses trivial for its users.
In this case taking the profile_lock when reading/writing class
attributes seems to be unnecessary.
Please remove the unnecessary locking inside the class attributes.
Before I respin a v7, let's make sure we're agreed on which things need
locking and which don't.
Functions that check if a lock is held:
_store_class_profile()
_notify_class_profile()
get_class_profile()
_aggregate_choices()
Functions that take a lock:
name_show()
choices_show()
profile_show()
profile_store()
platform_profile_choices_show()
platform_profile_show()
platform_profile_store()
platform_profile_cycle()
platform_profile_register()
platform_profile_remove()
Functions that don't take or check for a lock (these are intermediary
and things they call check for one):
_aggregate_profiles()
_store_and_notify()
Are you suggesting that basically these 4 can drop taking the lock?
name_show()
choices_show()
profile_show()
profile_store()
I think the show() ones I can get behind, but I'm worried about
profile_store(), particularly as it pertains to the other callers of
_store_class_profile() because it's incongruent how the other callers
would use it then.
Can we perhaps just drop it for the 3 class attribute show() ones?
LMK.
