Re: [BUG] gpiolib: cdev: can't read RELEASED event for last line

[Kent Gibson <warthog618@gmail.com>]

On Thu, May 25, 2023 at 03:46:12PM +0800, Kent Gibson wrote:
> On Thu, May 25, 2023 at 03:09:26PM +0800, Kent Gibson wrote:
> > On Thu, May 25, 2023 at 11:09:52AM +0800, Kent Gibson wrote:
> > > Hi Bart,
> > > 
> > I can also confirm that receiving the event using a blocking read() on the
> > fd still works, it is a poll() on the fd followed by a read() that fails.
> > 
> 
> Hmmm, so it occurred to me that gpionotify does the poll()/read(), so it
> should exhibit the bug.  But no, it doesn't.
> 
> So it could be my code doing something boneheaded??
> Or there is some other variable at play.
> I'll try to write a test for it with libgpiod and see I can reproduce
> it.  But I might put it on the back burner - this one isn't terribly
> high priority.
> 

Bisect result:

[bdbbae241a04f387ba910b8609f95fad5f1470c7] gpiolib: protect the GPIO device against being dropped while in use by user-space

So, the semaphores patch.
The Rust test gets the timings right to hit a race/order of events issue?

Cheers,
Kent.