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

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Message-ID: <alpine.LFD.2.00.0911302300550.24119@localhost.localdomain>
Date:	Mon, 30 Nov 2009 23:02:11 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc] "fair" rw spinlocks



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

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