Re: wait_event_interruptible() seems non-atomic

[Manfred Spraul <manfred@colorfullife.com>]

Hi Jan,

>I would like to also lock Buffer_lock around BufRP != BufWP, but don't see a
>way on how to accomplish this.
>
>  
>
This is not a problem: You compare BufRP and BufWP twice: once within 
wait_event_interruptible (without locking) and again a second test in 
your uif_read function with locking.
You are right that the test within wait_event_interruptible is 
optimistic: a concurrent uif_read could read the new data before the 
initial uif_read has a chance to acquire the BufferLock. But it doesn't 
matter: AFAICS the test is optimistic, it can't happen that BufRP and WP 
are actually different and wait_event sleeps. And the external loop 
within uif_read() just loops if the race that you describe happened.

Btw, could you post a link to the complete driver when asking questions? 
For example the use of down_interruptible() looks wrong to me, I'd use 
plain down().

--
    Manfred