Re: rw_semaphores

[Andrew Morton]

[e-mail] wrote:
> 
> On Tue, Apr 10, 2001 at 08:47:34AM +0100, David Howells wrote:
> >
> > Since you're willing to use CMPXCHG in your suggested implementation, would it
> > make it make life easier if you were willing to use XADD too?
> >
> > Plus, are you really willing to limit the number of readers or writers to be
> > 32767? If so, I think I can suggest a way that limits it to ~65535 apiece
> > instead...
> 
> I'm trying to imagine a case where 32,000 sharing a semaphore was anything but a
> major failure and I can't. To me: the result of an attempt by the 32,768th locker
> should be a kernel panic. Is there a reasonable scenario where this is wrong?
> 

It can't happen (famous last words).

- It is a bug for a task to acquire an rwsem more than once
  (either for read or write), so we don't do this.

- Linux only supports, err, 31700 user processes.