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

[Marc Kleine-Budde]

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.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |
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