Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761019AbYFWTXR (ORCPT ); Mon, 23 Jun 2008 15:23:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752245AbYFWTXG (ORCPT ); Mon, 23 Jun 2008 15:23:06 -0400 Received: from wf-out-1314.google.com ([209.85.200.175]:45853 "EHLO wf-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751321AbYFWTXD (ORCPT ); Mon, 23 Jun 2008 15:23:03 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=KR3Ja+FeeUVAodV5A4tI8okd06YNBSaGjzi2uaZZbn9gU6iqDtg77h2ifaHNxeuKWX PpJc/ggqWIv8OMX9Gic7KNrRF1NqTOgepFFbDj+yeMxRLNA+HlZdAm/1M5vP8+EpGXdQ A4vMFN/2gcaHIWnYz3sIk/wOcpVrhj0zMTuHk= Date: Mon, 23 Jun 2008 21:22:03 +0200 From: Marcin Slusarz To: Arjan van de Ven Cc: mchehab@infradead.org, linux-kernel@vger.kernel.org, Al Viro Subject: Re: [PATCH] Fix open/close race in saa7134 Message-ID: <20080623192141.GB5593@joi> References: <20080622100507.779acc59@infradead.org> <20080622172826.GA7487@joi> <20080622105832.1c61fb92@infradead.org> <20080623184937.GA5593@joi> <20080623115432.5ce376e5@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080623115432.5ce376e5@infradead.org> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2329 Lines: 55 On Mon, Jun 23, 2008 at 11:54:32AM -0700, Arjan van de Ven wrote: > On Mon, 23 Jun 2008 20:49:42 +0200 > Marcin Slusarz wrote: > > > 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 wrote: > > > > > > > On Sun, Jun 22, 2008 at 10:05:07AM -0700, Arjan van de Ven wrote: > > > > > > > > > > From: Arjan van de Ven > > > > > 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. > > this is not correct! > > this is a close->open race, not an open->close! > which means the guy who's closing it and the guy who's then opening it > again do not have to be the same guy If dev->empress_users could be > 1 then ok - it could break, but it can only be 1 or 0. If it's 1 you won't open the device. If it's 0 you won't reach ts_close. If you still see the race, please show me the sequence, because I don't (of course when decrementing is the last operation of ts_close). Marcin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/