Dead lock with clock global prepare_lock mutex and device's power.runtime_status

[Chen-Yu Tsai]

Hi,

On Mon, Jul 7, 2025 at 7:05 PM Marc Kleine-Budde <mkl at pengutronix.de> wrote:
>
> On 07.07.2025 18:58:16, Peng Fan wrote:
> > On Tue, Jul 01, 2025 at 03:16:08AM +0000, Carlos Song wrote:
> > >Hi, All:
> > >
> > >We met the dead lock issue recently and think it should be common issue and not sure how to fix it.
> > >
> > >We use gpio-gate-clock clock provider (drivers/clk/clk-gpio.c), gpio is one of i2c gpio expander (drivers/gpio/gpio-pcf857x.c). Our i2c driver enable run time pm (drivers/i2c/busses/i2c-imx-lpi2c.c [1]). System random blocked when at reboot.
> > >
> > >The dead lock happen as below call stacks
> > >
> > >Task 117                                                Task 120
> > >
> > >schedule()
> > >clk_prepare_lock()--> wait prepare_lock(mutex_lock)     schedule() wait for power.runtime_status exit RPM_SUSPENDING
> > >                           ^^^^ A                       ^^^^ B
> > >clk_bulk_unprepare()                                    rpm_resume()
> > >lpi2c_runtime_suspend()                                 pm_runtime_resume_and_get()
> > >...                                                     lpi2c_imx_xfer()
> > >                                                        ...
> > >rpm_suspend() set RPM_SUSPENDING                        pcf857x_set();
> > >                           ^^^^ B                       ...
> > >                                                        clk_prepare_lock() --> hold prepare_lock
> > >                                                        ^^^^ A
> > >                                                        ...
> > >
> >
> > This is a common issue that clk use a big prepare lock which is easy
> > to trigger dead lock with runtime pm. I recalled that pengutronix raised
> > this, but could not find the information.
>
> Alexander Stein stumbled over this issue some time ago:
>
> | https://lore.kernel.org/all/20230421-kinfolk-glancing-e185fd9c47b4-mkl@pengutronix.de/
>
> I encountered it too, while trying to add a clock provider driver for a
> SPI attached CAN controller which uses runtime pm.

Miquel from Bootlin posted a more formal description of the problem and
some possible solutions last year [1].

[1] https://lore.kernel.org/all/20240527181928.4fc6b5f0@xps-13/