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Message-ID: <Y4acZkkuUa5Peq+r@sol>
Date: Wed, 30 Nov 2022 07:57:26 +0800
From: Kent Gibson <warthog618@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.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 v3 2/2] gpiolib: protect the GPIO device against being
dropped while in use by user-space
On Tue, Nov 29, 2022 at 06:53:26PM +0200, Andy Shevchenko wrote:
> On Tue, Nov 29, 2022 at 01:35:53PM +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.
>
> ...
>
> I would do
>
> typedef __poll_t (*poll_fn)(struct file *, struct poll_table_struct *);
>
> and so on and use that one in the respective parameters.
>
> BUT. Since it's a fix, up to you which one to choose.
>
FWIW, the typedef looks cleaner to me too.
> > +static __poll_t call_poll_locked(struct file *file,
> > + struct poll_table_struct *wait,
> > + struct gpio_device *gdev,
> > + __poll_t (*func)(struct file *,
> > + struct poll_table_struct *))
> > +{
> > + __poll_t ret;
> > +
> > + down_read(&gdev->sem);
> > + ret = func(file, wait);
> > + up_read(&gdev->sem);
> > +
> > + return ret;
> > +}
>
> ...
>
> > + down_write(&gdev->sem);
>
> + Blank line?
>
Agreed.
> > /* FIXME: should the legacy sysfs handling be moved to gpio_device? */
> > gpiochip_sysfs_unregister(gdev);
> > gpiochip_free_hogs(gc);
>
> ...
>
> > gcdev_unregister(gdev);
>
> + Blank line ?
>
Disagree with this one though.
The comment prior to the gcdev_unregister() appears to apply to the block,
so the following lines should remain grouped.
Other than those nits, the series looks good to me.
Reviewed-by: Kent Gibson <warthog618@...il.com>
Cheers,
Kent.
> > + up_write(&gdev->sem);
> > put_device(&gdev->dev);
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
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