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Date: Mon, 30 Nov 2009 23:02:11 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@elte.hu>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Christoph Hellwig <hch@infradead.org>, Nick Piggin <npiggin@suse.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [rfc] "fair" rw spinlocks
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On Mon, 30 Nov 2009, Peter Zijlstra wrote:

> On Mon, 2009-11-30 at 22:12 +0100, Thomas Gleixner wrote:
> 
> > I think the conversion Linus proposed is pretty feasible. I went
> > through the read_lock sites and most of them are protecting function
> > calls which we already use under rcu_read_lock() in other places like
> > find_task* and thread or pid iterators.
> > 
> > There are a few non obvious ones in signal.c and posix-cpu-timers.c
> > (what a surprise) but nothing looks too scary.
> > 
> > If nobody beats me I'm going to let sed loose on the kernel, lift the
> > task_struct rcu free code from -rt and figure out what explodes.
> 
> Things like sched.c:tg_set_bandwidth() take the tasklist_lock in
> read-mode to exclude tasks being added concurrently to avoid
> sched_rt_can_attach() races with tg_has_rt_tasks().

Yeah, forgot to mention sched.c, but that's solvable
 
> Possibly the cgroup stuff has a smaller lock to use for this.

Worth checking.

Thanks,

	tglx