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

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Message-ID: <20091130182929.GD6762@linux.vnet.ibm.com>
Date:	Mon, 30 Nov 2009 10:29:29 -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 06:13:33PM +0100, Nick Piggin wrote:
> On Mon, Nov 30, 2009 at 09:05:57AM -0800, Linus Torvalds wrote:
> Secondly:
> 
> > 	static void tasklist_read_lock(void)
> > 	{
> > 		preempt_disable();
> > 		if (!current->tasklist_count++)
> 
> What happens if an interrupt and nested tasklist_read_lock() happens
> here?

Ouch!!!  This race affects the reader-writer-lock version as well.
Ah well, looks like interrupt disabling is required either way.

							Thanx, Paul
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