linux-kernel - Re: [rfc] "fair" rw spinlocks

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Date:	Mon, 30 Nov 2009 08:20:58 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc] "fair" rw spinlocks

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
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