linux-kernel - Re: [PATCH] driver core: platform: Use devres group to free driver probe resources

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Message-ID: <a20fc6ee-c6c3-4013-b175-4918b9a44380@tuxon.dev>
Date: Wed, 21 May 2025 08:41:33 +0300
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Ulf Hansson <ulf.hansson@...aro.org>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>,
 dakr@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, geert@...ux-m68k.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-iio@...r.kernel.org,
 bhelgaas@...gle.com
Subject: Re: [PATCH] driver core: platform: Use devres group to free driver
 probe resources

Hi, Ulf,

On 20.05.2025 15:09, Ulf Hansson wrote:
> For example, even if the order is made correctly, suppose a driver's
> ->remove() callback completes by turning off the resources for its
> device and leaves runtime PM enabled, as it relies on devres to do it
> some point later. Beyond this point, nothing would prevent userspace
> for runtime resuming/suspending the device via sysfs. 

If I'm not wrong, that can't happen? The driver_sysfs_remove() is called
before device_remove() (which calls the driver remove) is called, this
being the call path:

device_driver_detach() ->
  device_release_driver_internal() ->
    __device_release_driver() ->
      driver_sysfs_remove()
      // ...
      device_remove()

And the driver_sysfs_remove() calls in the end __kernfs_remove() which
looks to me like the place that actually drops the entries from sysfs, this
being a call path for it:

driver_sysfs_remove() ->
  sysfs_remove_link() ->
    kernfs_remove_by_name() ->
      kernfs_remove_by_name_ns() ->
        __kernfs_remove() ->

activating the following line in __kernfs_remove():

pr_debug("kernfs %s: removing\n", kernfs_rcu_name(kn));

leads to the following prints when unbinding the watchdog device from its
watchdog driver (attached to platform bus) on my board:
https://p.fr33tux.org/935252

Thank you,
Claudiu