linux-kernel - Re: [PATCH] gpiolib: tie module references to GPIO devices, not requested descs

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Message-ID: <ZOMxue7lvHFWMCCb@smile.fi.intel.com>
Date:   Mon, 21 Aug 2023 12:43:21 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: tie module references to GPIO devices, not
 requested descs

On Fri, Aug 18, 2023 at 09:01:08PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> After a deeper look at commit 3386fb86ecde ("gpiolib: fix reference
> leaks when removing GPIO chips still in use") I'm now convinced that
> gpiolib gets module reference counting wrong.
> 
> As we only take the reference to the owner module when a descriptor is
> requested and put it when it's freed, we can easily trigger a crash by
> removing a module which registered a driver bound to a GPIO chip which
> is unused as nothing prevents us from doing so.
> 
> For correct behavior, we should take the reference to the module when
> we're creating a GPIO device and only put it when that device is
> released as it's at this point that we can safely remove the module's
> code from memory.

Two cases to consider:
1) legacy gpio_*() APIs, do they suppose to create a GPIO device?
2) IRQ request without GPIO being requested, is it the case?

Seems to me that the 1) is the case, while 2) is not.

-- 
With Best Regards,
Andy Shevchenko