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
next prev parent 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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