Re: [PATCH v6 11/22] ACPI: platform_profile: Add name attribute to class interface

[Armin Wolf]

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.

Thanks,
Armin Wolf

> Thanks,
> Armin Wolf
>
> > +}
> > +
> > +static DEVICE_ATTR_RO(name);
> > +static struct attribute *profile_attrs[] = {
> > +    &dev_attr_name.attr,
> > +    NULL
> > +};
> > +ATTRIBUTE_GROUPS(profile);
> > +
> >   static const struct class platform_profile_class = {
> >       .name = "platform-profile",
> > +    .dev_groups = profile_groups,
> >   };
> >
> >   static ssize_t platform_profile_choices_show(struct device *dev,