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From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Kent Gibson <warthog618@gmail.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>
Subject: Re: [PATCH v2 07/11] gpiolib: rework the locking mechanism for lineevent kfifo
Date: Thu, 5 Dec 2019 00:25:46 +0200
Message-ID: <CAHp75Vf7+XY8rnrbMfMgNO25EHSemjZVUgvFFp+zvj4vvJ1B8g@mail.gmail.com> (raw)
In-Reply-To: <20191204155912.17590-8-brgl@bgdev.pl>

On Wed, Dec 4, 2019 at 6:01 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>
> The read_lock mutex is supposed to prevent collisions between reading
> and writing to the line event kfifo but it's actually only taken when
> the events are being read from it.
>
> Drop the mutex entirely and reuse the spinlock made available to us in
> the waitqueue struct. Take the lock whenever the fifo is modified or
> inspected. Drop the call to kfifo_to_user() and instead first extract
> the new element from kfifo when the lock is taken and only then pass
> it on to the user after the spinlock is released.
>

My comments below.

> +       spin_lock(&le->wait.lock);
>         if (!kfifo_is_empty(&le->events))
>                 events = EPOLLIN | EPOLLRDNORM;
> +       spin_unlock(&le->wait.lock);

Sound like a candidate to have kfifo_is_empty_spinlocked().


>         struct lineevent_state *le = filep->private_data;
> -       unsigned int copied;
> +       struct gpioevent_data event;
>         int ret;

> +       if (count < sizeof(event))
>                 return -EINVAL;

This still has an issue with compatible syscalls. See patch I have
sent recently.
I dunno how you see is the better way: a) apply mine and rebase your
series, or b) otherwise.
I can do b) if you think it shouldn't be backported.

Btw, either way we have a benifits for the following one (I see you
drop kfifo_to_user() and add event variable on stack).

> +       return sizeof(event);

Also see comments in my patch regarding the event handling.

-- 
With Best Regards,
Andy Shevchenko

  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-04 15:59 [PATCH v2 00/11] gpiolib: add an ioctl() for monitoring line status changes Bartosz Golaszewski
2019-12-04 15:59 ` [PATCH v2 01/11] gpiolib: use 'unsigned int' instead of 'unsigned' in gpio_set_config() Bartosz Golaszewski
2019-12-04 22:18   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 02/11] gpiolib: have a single place of calling set_config() Bartosz Golaszewski
2019-12-04 22:18   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 03/11] gpiolib: convert the type of hwnum to unsigned int in gpiochip_get_desc() Bartosz Golaszewski
2019-12-04 22:19   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 04/11] gpiolib: use gpiochip_get_desc() in linehandle_create() Bartosz Golaszewski
2019-12-04 22:20   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 05/11] gpiolib: use gpiochip_get_desc() in lineevent_create() Bartosz Golaszewski
2019-12-04 22:20   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 06/11] gpiolib: use gpiochip_get_desc() in gpio_ioctl() Bartosz Golaszewski
2019-12-04 16:25   ` Rainer Sickinger
2019-12-04 22:21   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 07/11] gpiolib: rework the locking mechanism for lineevent kfifo Bartosz Golaszewski
2019-12-04 22:25   ` Andy Shevchenko [this message]
2019-12-05  9:31     ` Bartosz Golaszewski
2019-12-05 10:22       ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 08/11] gpiolib: emit a debug message when adding events to a full kfifo Bartosz Golaszewski
2019-12-04 22:28   ` Andy Shevchenko
2019-12-04 15:59 ` [PATCH v2 09/11] gpiolib: provide a dedicated function for setting lineinfo Bartosz Golaszewski
2019-12-04 22:30   ` Andy Shevchenko
2019-12-05  9:28     ` Bartosz Golaszewski
2019-12-05 10:20       ` Andy Shevchenko
2019-12-05 13:45         ` Bartosz Golaszewski
2019-12-05 16:47           ` Andy Shevchenko

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