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

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Date:	Mon, 30 Nov 2009 22:27:09 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
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, 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().

Possibly the cgroup stuff has a smaller lock to use for this.

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