linux-kernel - Re: [PATCH] parport/ppdev: fix registration of sysctl entries

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Message-ID: <20080706203508.GB28946@ZenIV.linux.org.uk>
Date:	Sun, 6 Jul 2008 21:35:08 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Frans Pop <elendil@...net.nl>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] parport/ppdev: fix registration of sysctl entries

On Sun, Jul 06, 2008 at 05:07:02PM +0200, Marcin Slusarz wrote:
> On Sun, Jul 06, 2008 at 01:11:48AM +0100, Al Viro wrote:
> > On Sun, Jul 06, 2008 at 12:51:48AM +0100, Al Viro wrote:
> > 
> > > I don't believe that it's right.  Note that if you *do* race there, you
> > > are fucked regardless of sysctls - ppdev.c::register_device() racing
> > > with itself will do tons of fun things all by itself (starting with two
> > > threads allocating different pdev and both setting pp->pdev).
> 
> I wouldn't call it a race - BKL is protecting multiple ioctl calls, so we
> won't ever claim the device from two different threads.

Yes, we can - register_device() does kmalloc() with GFP_KERNEL, which kills
any protection from BKL.  BKL is _not_ providing any kind of exclusion while
you sleep.
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