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

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Message-ID: <29899120-efec-4264-b6a8-0bca4fc1f332@gmx.de>
Date: Mon, 18 Nov 2024 20:43:24 +0100
From: Armin Wolf <W_Armin@....de>
To: Mario Limonciello <mario.limonciello@....com>,
 Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Maximilian Luz <luzmaximilian@...il.com>, Lee Chun-Yi <jlee@...e.com>,
 Shyam Sundar S K <Shyam-sundar.S-k@....com>,
 Corentin Chary <corentin.chary@...il.com>, "Luke D . Jones"
 <luke@...nes.dev>, Ike Panhc <ike.pan@...onical.com>,
 Henrique de Moraes Holschuh <hmh@....eng.br>,
 Alexis Belmonte <alexbelm48@...il.com>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Ai Chao <aichao@...inos.cn>, Gergo Koteles <soyer@....hu>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:ACPI" <linux-acpi@...r.kernel.org>,
 "open list:MICROSOFT SURFACE PLATFORM PROFILE DRIVER"
 <platform-driver-x86@...r.kernel.org>,
 "open list:THINKPAD ACPI EXTRAS DRIVER"
 <ibm-acpi-devel@...ts.sourceforge.net>,
 Mark Pearson <mpearson-lenovo@...ebb.ca>,
 Matthew Schwartz <matthew.schwartz@...ux.dev>
Subject: Re: [PATCH v6 11/22] ACPI: platform_profile: Add name attribute to
 class interface

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@...ebb.ca>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>   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?

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,