Re: cdev/devm_* issues (was Re: [TECH TOPIC] Rust for Linux)

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Jul 14, 2021 at 12:35 AM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:

> To me described scenario sounds rather like an object lifetime possible issue.
> In any case, shouldn’t VFS guarantee by a reference counting that
> gpiochip_remove() wouldn’t be called while file descriptor is in use?
> Or am I looking from the wrong end here?

What happens is that the GPIO device disappears (such as unplugging
a USB GPIO expander) while a multithreaded userspace is hammering
exotic ioctl() commands to the same device like crazy.

Under these circumstances (which should be rare, but you know,
developers) it could happen that an ioctl() sneak in before the
gpio_chip pointer is NULL if I read the code right.

Yours,
Linus Walleij