linux-kernel - Re: [PATCH v2 0/3] gpiolib: use a read-write semaphore to protect the GPIO device list

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Message-ID: <CAMRc=Mfj6Fik0qfFiC_LvBiBdr5PP2sqNNAPQpKzignmwHCajA@mail.gmail.com>
Date: Thu, 4 Jan 2024 10:39:27 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 0/3] gpiolib: use a read-write semaphore to protect the
 GPIO device list

On Tue, Jan 2, 2024 at 4:59 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> I'm still figuring out how to keep GPIO descriptors coherent while
> (mostly) lockless. In the meantime, I found a potential race-condition
> during GPIO descriptor lookup and also figured that the correct way to
> protect the GPIO device list is actually a read-write semaphore as we're
> not modifying the list very often and readers should be able to iterate
> over it concurrently.
>
> The first patch in this series is new in v2. I realized that we must not
> wait until .release() to remove the GPIO device from the list as this is
> why pinning down the GPIO device list during lookup would never work -
> we always could end up re-taking a reference to an object that was being
> released if it got looked up between when the last reference is dropped
> and the object is finally removed from the device list.
>
> v1 -> v2:
> - add patch 1/3 to fix a release timing issue
>
> Bartosz Golaszewski (3):
>   gpiolib: remove the GPIO device from the list when it's unregistered
>   gpiolib: replace the GPIO device mutex with a read-write semaphore
>   gpiolib: pin GPIO devices in place during descriptor lookup
>
>  drivers/gpio/gpiolib-sysfs.c |  2 +-
>  drivers/gpio/gpiolib.c       | 62 ++++++++++++++++++++----------------
>  drivers/gpio/gpiolib.h       |  2 +-
>  3 files changed, 36 insertions(+), 30 deletions(-)
>
> --
> 2.40.1
>

Series applied.

Bart