linux-kernel - Re: [PATCH] Fix open/close race in saa7134

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Message-ID: <20080623184937.GA5593@joi>
Date:	Mon, 23 Jun 2008 20:49:42 +0200
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	mchehab@...radead.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@....linux.org.uk>
Subject: Re: [PATCH] Fix open/close race in saa7134

On Sun, Jun 22, 2008 at 10:58:32AM -0700, Arjan van de Ven wrote:
> On Sun, 22 Jun 2008 19:33:37 +0200
> Marcin Slusarz <marcin.slusarz@...il.com> wrote:
> 
> > On Sun, Jun 22, 2008 at 10:05:07AM -0700, Arjan van de Ven wrote:
> > > 
> > > From: Arjan van de Ven <arjan@...ux.intel.com>
> > > Date: Sun, 22 Jun 2008 10:03:02 -0700
> > > Subject: [PATCH] Fix open/close race in saa7134
> > > 
> > > The saa7134 driver uses a (non-atomic) variable in an attempt to
> > > only allow one opener of the device (how it deals with sending
> > > the fd over unix sockets I don't know).
> > > 
> > > Unfortunately, the release function first decrements this variable,
> > > and THEN goes on to disable more of the device. This allows for
> > > a race where another opener of the device comes in after the
> > > decrement of the variable, configures the hardware just to then see
> > > the hardware be disabled by the rest of the release function.
> > 
> > Simplier fix:
> > http://lkml.org/lkml/2008/6/9/308
> > But I don't remember whether it was applied or not...
> 
> 
> the patch might be simpler, but it's not fully correct...
> the decrement is non-atomic and not protected by any lock whatsoever.

It's not atomic, but it don't have to, because there's only one thread which
"owns" the device. But I agree that having a mutex here makes locking more obvious.

PS: Thanks for fixing kerneloops.org.

Marcin
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