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SubjectRe: [PATCH v2 07/11] gpiolib: rework the locking mechanism for lineevent kfifo
On Wed, Dec 4, 2019 at 6:01 PM Bartosz Golaszewski <> wrote:
> From: Bartosz Golaszewski <>
> 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))
> + 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

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