linux-kernel - Re: [PATCH v2] gpiolib: Avoid side effects in gpio_is

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Date:   Fri, 19 May 2023 13:08:50 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Chris Packham <chris.packham@...iedtelesis.co.nz>
Cc:     linus.walleij@...aro.org, brgl@...ev.pl, johan@...nel.org,
        maz@...nel.org, warthog618@...il.com, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] gpiolib: Avoid side effects in gpio_is_visible()

On Fri, May 19, 2023 at 8:07 AM Chris Packham
<chris.packham@...iedtelesis.co.nz> wrote:
>
> On a system with pca9555 GPIOs that have been exported via sysfs the
> following warning could be triggered on kexec().
>
>   WARNING: CPU: 0 PID: 265 at drivers/gpio/gpiolib.c:3411 gpiochip_disable_irq
>   Call trace:
>    gpiochip_disable_irq
>    machine_crash_shutdown
>    __crash_kexec
>    panic
>    sysrq_reset_seq_param_set
>    __handle_sysrq
>    write_sysrq_trigger
>
> The warning is triggered because there is an irq_desc for the GPIO but
> it does not have the FLAG_USED_AS_IRQ set. This is because when the GPIO
> is exported via gpiod_export(), gpio_is_visible() is used to determine
> if the "edge" attribute should be provided but in doing so it ends up
> calling gpiochip_to_irq() which creates the irq_desc.
>
> Remove the call to gpiod_to_irq() from gpio_is_visible(). The actual
> intended creation of the irq_desc comes via edge_store() when requested
> by the user.

To me it still sounds like a hack and the real solution should be done
differently/elsewhere.

Also I'm worrying that not having this file visible or not may affect
existing user space custom scripts we will never hear about.

P.S. TBH, I don't care much about sysfs, so if this patch finds its
way upstream, I won't be unhappy.

-- 
With Best Regards,
Andy Shevchenko