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Message-ID: <ZNt2KQMtpMdK9TyY@smile.fi.intel.com>
Date: Tue, 15 Aug 2023 15:57:13 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: Bartosz Golaszewski <brgl@...ev.pl>,
Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3] gpiolib: fix reference leaks when removing GPIO chips
still in use
On Tue, Aug 15, 2023 at 01:40:22PM +0200, Linus Walleij wrote:
> On Tue, Aug 15, 2023 at 11:50 AM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > On Fri, Aug 11, 2023 at 09:30:34PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > After we remove a GPIO chip that still has some requested descriptors,
> > > gpiod_free_commit() will fail and we will never put the references to the
> > > GPIO device and the owning module in gpiod_free().
> > >
> > > Rework this function to:
> > > - not warn on desc == NULL as this is a use-case on which most free
> > > functions silently return
> > > - put the references to desc->gdev and desc->gdev->owner unconditionally
> > > so that the release callback actually gets called when the remaining
> > > references are dropped by external GPIO users
...
> > > - if (desc && desc->gdev && gpiod_free_commit(desc)) {
> >
> > The commit message doesn't explain disappearing of gdev check.
> >
> > > - module_put(desc->gdev->owner);
> > > - gpio_device_put(desc->gdev);
> > > - } else {
> > > + /*
> > > + * We must not use VALIDATE_DESC_VOID() as the underlying gdev->chip
> > > + * may already be NULL but we still want to put the references.
> > > + */
> > > + if (!desc)
> > > + return;
> > > +
> > > + if (!gpiod_free_commit(desc))
> > > WARN_ON(extra_checks);
> > > - }
> > > +
> > > + module_put(desc->gdev->owner);
> > > + gpio_device_put(desc->gdev);
> > > }
> >
> > So, if gdev can be NULL, you will get an Oops with new code.
>
> I read it such that gdev->chip can be NULL, but not gdev,
> and desc->gdev->owner is fine to reference?
Basically the Q is
"if desc is non-NULL, does it guarantee that gdev is non-NULL either?"
--
With Best Regards,
Andy Shevchenko
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