linux-kernel - Re: [PATCH v3 01/24] gpio: protect the list of GPIO devices with SRCU

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Message-ID: <CAMRc=Mc2MjvicHyWrt813LRHqzfexUUcR49N6+JF62f5tPYt0g@mail.gmail.com>
Date: Sat, 10 Feb 2024 12:07:39 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Hillf Danton <hdanton@...a.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, "Paul E . McKenney" <paulmck@...nel.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Wolfram Sang <wsa@...-dreams.de>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 01/24] gpio: protect the list of GPIO devices with SRCU

On Sat, Feb 10, 2024 at 12:01 PM Hillf Danton <hdanton@...a.com> wrote:
>
> On Thu,  8 Feb 2024 10:58:57 +0100 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > @@ -382,11 +389,13 @@ static int gpiodev_add_to_list_unlocked(struct gpio_device *gdev)
> >               /* add between prev and next */
> >               if (prev->base + prev->ngpio <= gdev->base
> >                               && gdev->base + gdev->ngpio <= next->base) {
> > -                     list_add(&gdev->list, &prev->list);
> > +                     list_add_rcu(&gdev->list, &prev->list);
> >                       return 0;
> >               }
> >       }
> >
> > +     synchronize_srcu(&gpio_devices_srcu);
> > +
> If not typo, could you shed light on why this sync is needed?
>

No it's not a typo. I'm not an expert on RCU but I figured that right
after we add the new element to the SRCU-protected list, we need to
wait for all read-only critical sections to complete before
continuing? Is that not correct?

Bart

> >       return -EBUSY;
> >  }
>