Re: [PATCH] serial: qcom-geni: fix enabling deactivated interrupt

[Stephen Boyd]

Quoting Krzysztof Kozlowski (2023-05-05 08:23:01)
> The driver have a race, experienced only with PREEMPT_RT patchset:
>
> CPU0                         | CPU1
> ==================================================================
> qcom_geni_serial_probe       |
>   uart_add_one_port          |
>                              | serdev_drv_probe
>                              |   qca_serdev_probe
>                              |     serdev_device_open
>                              |       uart_open
>                              |         uart_startup
>                              |           qcom_geni_serial_startup
>                              |             enable_irq
>                              |               __irq_startup
>                              |                 WARN_ON()
>                              |                 IRQ not activated
>   request_threaded_irq       |
>     irq_domain_activate_irq  |
>
> The warning:
>
>   894000.serial: ttyHS1 at MMIO 0x894000 (irq = 144, base_baud = 0) is a MSM
>   serial serial0: tty port ttyHS1 registered
>   WARNING: CPU: 7 PID: 107 at kernel/irq/chip.c:241 __irq_startup+0x78/0xd8
>   ...
>   qcom_geni_serial 894000.serial: serial engine reports 0 RX bytes in!
>
> Adding UART port triggers probe of child serial devices - serdev and
> eventually Qualcomm Bluetooth hci_qca driver.  This opens UART port
> which enables the interrupt before it got activated in
> request_threaded_irq().  The issue originates in commit f3974413cf02
> ("tty: serial: qcom_geni_serial: Wakeup IRQ cleanup") and discussion on
> mailing list [1].  However the above commit does not explain why the
> uart_add_one_port() is moved above requesting interrupt.
>
> [1] https://lore.kernel.org/all/5d9f3dfa.1c69fb81.84c4b.30bf@xxxxxxxxxxxxx/
>
> Fixes: f3974413cf02 ("tty: serial: qcom_geni_serial: Wakeup IRQ cleanup")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> ---

Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>