Re: [rfc] "fair" rw spinlocks

Paul E. McKenney
2009-11-30T16:20:58Z

On Mon, Nov 30, 2009 at 08:55:57AM +0100, Nick Piggin wrote:
> On Sat, Nov 28, 2009 at 09:30:18AM -0800, Linus Torvalds wrote:
> > So as far as I can tell, we have only one real user of rwlocks where
> > livelocks might be relevant, but that one real user absolutely _requires_
> > the unfair behavior.
>
> Yes, although the behaviour required is that it can be recursively
> acquired. So we could still have a lock that disallows new non recursive
> read acquires when there is a pending write locker.
>
> RCU seems nicer, but tasklist lock locking scares me so I wanted to fix
> it the easy way :)

Having a livelock-free tasklist lock would certainly make it easier
to apply things like RCU on a code-path-by-code-path basis as needed.
Much less scary than a big-bang rip-and-replace.

Thanx, Paul