Re: [PATCH v7 0/8] devm_led_classdev_register() usage problem

[George Stark]

Hello Lee

On 4/11/24 16:45, Lee Jones wrote:
> On Fri, 29 Mar 2024, George Stark wrote:
>
> > Hello Lee
> >
> > On 3/22/24 13:43, Lee Jones wrote:
> > > On Fri, 22 Mar 2024, George Stark wrote:
> > >
> > > > Hello Lee
> > > >
> > > > On 3/21/24 21:11, Lee Jones wrote:
> > > > > On Thu, 14 Mar 2024, George Stark wrote:
> > > > >
> > > > > > This patch series fixes the problem of devm_led_classdev_register misusing.
> > > > > >
> > > > > > The basic problem is described in [1]. Shortly when devm_led_classdev_register()
> > > > > > is used then led_classdev_unregister() called after driver's remove() callback.
> > > > > > led_classdev_unregister() calls driver's brightness_set callback and that callback
> > > > > > may use resources which were destroyed already in driver's remove().
> > > > > >
> > > > > > After discussion with maintainers [2] [3] we decided:
> > > > > > 1) don't touch led subsystem core code and don't remove led_set_brightness() from it
> > > > > > but fix drivers
> > > > > > 2) don't use devm_led_classdev_unregister
> > > > > >
> > > > > > So the solution is to use devm wrappers for all resources
> > > > > > driver's brightness_set() depends on. And introduce dedicated devm wrapper
> > > > > > for mutex as it's often used resource.
> > > >
> > > > ...
> > > >
> > > > > >      locking/mutex: introduce devm_mutex_init()
> > > > > >      leds: aw2013: use devm API to cleanup module's resources
> > > > > >      leds: aw200xx: use devm API to cleanup module's resources
> > > > > >      leds: lp3952: use devm API to cleanup module's resources
> > > > > >      leds: lm3532: use devm API to cleanup module's resources
> > > > > >      leds: nic78bx: use devm API to cleanup module's resources
> > > > > >      leds: mlxreg: use devm_mutex_init() for mutex initialization
> > > > > >      leds: an30259a: use devm_mutex_init() for mutex initialization
> > > > > >
> > > > > >     drivers/leds/leds-an30259a.c | 14 ++++----------
> > > > > >     drivers/leds/leds-aw200xx.c  | 32 +++++++++++++++++++++-----------
> > > > > >     drivers/leds/leds-aw2013.c   | 25 +++++++++++++------------
> > > > > >     drivers/leds/leds-lm3532.c   | 29 +++++++++++++++++------------
> > > > > >     drivers/leds/leds-lp3952.c   | 21 +++++++++++----------
> > > > > >     drivers/leds/leds-mlxreg.c   | 14 +++++---------
> > > > > >     drivers/leds/leds-nic78bx.c  | 23 +++++++++++++----------
> > > > > >     include/linux/mutex.h        | 27 +++++++++++++++++++++++++++
> > > > > >     kernel/locking/mutex-debug.c | 11 +++++++++++
> > > > > >     9 files changed, 122 insertions(+), 74 deletions(-)
> > > > >
> > > > > Doesn't apply to v6.8.
> > > > >
> > > > > What base was used for this?
> > > >
> > > > I've just pulled git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > > > and v7 was applied cleanly. linux-next is ok too.
> > > >
> > > > v6.8 is lack of recent patch 6969d0a2ba1adc9ba6a49b9805f24080896c255c
> > > > v7's patch #2 depends on it
> > >
> > > No problem.  I'll wait for v6.9-rc1.
> >
> > Just checked the v7 patch series on released 6.9-rc1 and it's applied
> > cleanly. If anything i can help please let me know.
>
> It applies, but doesn't seem to build:
>
> make --silent --keep-going --jobs=8 O=../build ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CROSS_COMPILE_COMPAT=arm-linux-gnueabihf- 'CC=sccache aarch64-linux-gnu-gcc' 'HOSTCC=sccache gcc' allmodconfig
> make --silent --keep-going --jobs=8 O=../build ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CROSS_COMPILE_COMPAT=arm-linux-gnueabihf- 'CC=sccache aarch64-linux-gnu-gcc' 'HOSTCC=sccache gcc'
> ERROR: modpost: "__devm_mutex_init" [drivers/leds/leds-an30259a.ko] undefined!
> ERROR: modpost: "__devm_mutex_init" [drivers/leds/leds-aw200xx.ko] undefined!
> ERROR: modpost: "__devm_mutex_init" [drivers/leds/leds-aw2013.ko] undefined!
> ERROR: modpost: "__devm_mutex_init" [drivers/leds/leds-lm3532.ko] undefined!
> ERROR: modpost: "__devm_mutex_init" [drivers/leds/leds-mlxreg.ko] undefined!
> make[3]: *** [/builds/linux/scripts/Makefile.modpost:145: Module.symvers] Error 1
>
> Did you forget to export it?

Yes, my bad. I tested *DEBUG* configs but without modules enabled.
Adding EXPORT_SYMBOL_GPL(__devm_mutex_init); fixes the problem,
v8 is on the way.

--
Best regards
George