lkml.org 
[lkml]   [2019]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2 07/11] gpiolib: rework the locking mechanism for lineevent kfifo
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

\
 
 \ /
  Last update: 2019-12-04 23:26    [W:0.104 / U:6.560 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site