linux-kernel - Re: [PATCH v7 2/2] gpiolib: protect the GPIO device against being dropped while in use by user-space

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Date:   Fri, 2 Dec 2022 17:44:58 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nick Hainke <vincent@...temli.org>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v7 2/2] gpiolib: protect the GPIO device against being
 dropped while in use by user-space

On Fri, Dec 02, 2022 at 04:04:44PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> While any of the GPIO cdev syscalls is in progress, the kernel can call
> gpiochip_remove() (for instance, when a USB GPIO expander is disconnected)
> which will set gdev->chip to NULL after which any subsequent access will
> cause a crash.
> 
> To avoid that: use an RW-semaphore in which the syscalls take it for
> reading (so that we don't needlessly prohibit the user-space from calling
> syscalls simultaneously) while gpiochip_remove() takes it for writing so
> that it can only happen once all syscalls return.
> 
> Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines")
> Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL")
> Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
> Fixes: a54756cb24ea ("gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL")
> Fixes: 7b8e00d98168 ("gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> [Nick: fixed a build failure with CDEV_V1 disabled]

> Co-authored-by: Nick Hainke <vincent@...temli.org>

In Linux kernel there is no such tag. And in case you want to use
Co-developed-by, you also need to add the respective SoB one.

> Reviewed-by: Kent Gibson <warthog618@...il.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

-- 
With Best Regards,
Andy Shevchenko