linux-kernel - Re: RFC: Fix f_flags races without the BKL

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Date:	Tue, 30 Dec 2008 05:49:46 -0700
From:	Jonathan Corbet <corbet@....net>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Al Viro <viro@...IV.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>, bfields@...ldses.org,
	xfs-masters@....sgi.com
Subject: Re: RFC: Fix f_flags races without the BKL

On Mon, 29 Dec 2008 12:57:06 +0100
Sam Ravnborg <sam@...nborg.org> wrote:

> Rather than open coded mutex how about adding a few helpers to
> set and clear the flags and hide locking there?

There's a couple of problems with that.  One being that SETFL wants to
manipulate a bunch of flags together, so a simple set_flag/clear_flag
interface won't do it.  Beyond that, though, calls to the ->fasync()
function need to be atomic with respect to changes to the associated
flag.

Still, it seems that the global lock approach isn't too popular, so
I'll get back to the drawing board once I'm theoretically not on
vacation.

Thanks,

jon
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