linux-kernel - Re: [PATCH v2 0/4] gpio: fix SRCU bugs

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Message-ID: <ef420f58-cf5a-4bd3-adc4-b9ef651498ca@paulmck-laptop>
Date: Wed, 14 Feb 2024 12:44:09 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>,
	Kent Gibson <warthog618@...il.com>, Alex Elder <elder@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Wolfram Sang <wsa@...-dreams.de>, Mark Brown <broonie@...nel.org>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 0/4] gpio: fix SRCU bugs

On Wed, Feb 14, 2024 at 08:08:33PM +0100, Bartosz Golaszewski wrote:
> On Wed, Feb 14, 2024 at 7:44 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Wed, Feb 14, 2024 at 09:44:15AM +0100, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > Here are four fixes to some bugs in recent SRCU changes. The first one fixes
> > > an actual race condition. The other three just make lockdep happy.
> >
> > For 1/4-3/4:
> >
> > Acked-by: Paul E. McKenney <paulmck@...nel.org>
> >
> > For 4/4, you are playing with fire, but I will assume that you know what
> > you are doing.  ;-)
> 
> Up until this rework, this gdev->chip pointer could go from under any
> user at any point. Now we have this gpio_device wrapper that provides
> an entry point to using the chip safely while protected by the SRCU
> read lock. Anyone who is still accessing gpio_chip directly (and not
> being the GPIO provider themselves) is asking for trouble. There's
> however no point in spamming lockdep splats in this case. I may end up
> adding a warning to these routines.
> 
> Unfortunately, it's hard to fix 15 years of technical debt. :(

Indeed, life is sometimes hard!

							Thanx, Paul

> Thanks for the Acks.
> Bartosz
> 
> [snip]