[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <Y4dGNy4vlDEUUFlw@smile.fi.intel.com>
Date: Wed, 30 Nov 2022 14:01:59 +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>,
linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v4 2/2] gpiolib: protect the GPIO device against being
dropped while in use by user-space
On Wed, Nov 30, 2022 at 10:05:56AM +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.
Bikeshedding below and one question.
(As per tag I'm fine with this version anyway)
...
> +typedef __poll_t (*poll_fn)(struct file *, struct poll_table_struct *);
> +typedef long (*ioctl_fn)(struct file *, unsigned int, unsigned long);
> +typedef ssize_t (*read_fn)(struct file *, char __user *,
> + size_t count, loff_t *);
<bikeshedding>
It's only 84 is on a single line.
Dunno if it's better to have typedef followed by wrapper pairs rather than
all typedefs and wrappers grouped.
</bikeshedding>
> +static __poll_t call_poll_locked(struct file *file,
> + struct poll_table_struct *wait,
> + struct gpio_device *gdev, poll_fn func)
> +{
> + __poll_t ret;
> + down_read(&gdev->sem);
Thinking more about this, wouldn't be better to actually
ret = down_read_trylock(&gdev->sem);
if (ret)
return ret;
?
> + ret = func(file, wait);
> + up_read(&gdev->sem);
> +
> + return ret;
> +}
--
With Best Regards,
Andy Shevchenko
Powered by blists - more mailing lists