Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496AbZJVC1W (ORCPT ); Wed, 21 Oct 2009 22:27:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751842AbZJVC1V (ORCPT ); Wed, 21 Oct 2009 22:27:21 -0400 Received: from mail-px0-f179.google.com ([209.85.216.179]:52370 "EHLO mail-px0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751582AbZJVC1U convert rfc822-to-8bit (ORCPT ); Wed, 21 Oct 2009 22:27:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=AynoODxiu6DfrBpPMgIBjDQrp3sVL/KKLoknYkjZp9Lj2MAz78SQkl229/5yABq9mB S/6B4T0DVDY73n/SviOD2hfJ2IrXd1TNrux62HuKsEISd/7C3yI2Knqw99Imz9gW/14N Fu9ITJfFnHC2Cf/Vch8a8W6X4t4sGgQ6Cid1Y= MIME-Version: 1.0 In-Reply-To: <4ADF35CA.5020207@imap.cc> References: <4ADB93C4.4090607@imap.cc> <7b6bb4a50910182227y1281b40bj3fcc082d32cf4496@mail.gmail.com> <4ADF35CA.5020207@imap.cc> Date: Thu, 22 Oct 2009 10:27:25 +0800 Message-ID: <7b6bb4a50910211927k7371aeax1973b295c6f729c@mail.gmail.com> Subject: Re: possible circular locking dependency in ISDN PPP From: Xiaotian Feng To: Tilman Schmidt Cc: LKML , isdn4linux , Netdev , Karsten Keil Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2673 Lines: 65 On Thu, Oct 22, 2009 at 12:24 AM, Tilman Schmidt wrote: > Thanks for your analysis. The patch you propose does indeed prevent the > "circular locking dependency" message, with no noticeable ill effect. > > I cannot say why xmit_lock was taken around isdn_net_lp_busy() in the > first place. The ISDN4Linux people would be the ones to comment on that. > If none of them objects, I propose you add a Signed-off-by line to your > patch and submit it to Karsten Keil, the ISDN maintainer, for inclusion. > You can also add a "Tested-by: Tilman Schmidt " line. > Sure, I'll prepare a patch and send to Karsten later, Thanks. > Thanks, > Tilman > > Am 19.10.2009 07:27 schrieb Xiaotian Feng: >> So there's a circular locking dependency.. Looking into isdn_net_get_locked_lp() > [...] >> Why do we need to hold xmit_lock while using >> isdn_net_lp_busy(nd->queue) ? Can following patch fix this bug? >> >> --- >> diff --git a/drivers/isdn/i4l/isdn_net.h b/drivers/isdn/i4l/isdn_net.h >> index 74032d0..7511f08 100644 >> --- a/drivers/isdn/i4l/isdn_net.h >> +++ b/drivers/isdn/i4l/isdn_net.h >> @@ -83,19 +83,19 @@ static __inline__ isdn_net_local * >> isdn_net_get_locked_lp(isdn_net_dev *nd) >> >>         spin_lock_irqsave(&nd->queue_lock, flags); >>         lp = nd->queue;         /* get lp on top of queue */ >> -       spin_lock(&nd->queue->xmit_lock); >>         while (isdn_net_lp_busy(nd->queue)) { >> -               spin_unlock(&nd->queue->xmit_lock); >>                 nd->queue = nd->queue->next; >>                 if (nd->queue == lp) { /* not found -- should never happen */ >>                         lp = NULL; >>                         goto errout; >>                 } >> -               spin_lock(&nd->queue->xmit_lock); >>         } >>         lp = nd->queue; >>         nd->queue = nd->queue->next; >> +       spin_unlock_irqrestore(&nd->queue_lock, flags); >> +       spin_lock(&lp->xmit_lock); >>         local_bh_disable(); >> +       return lp; >>  errout: >>         spin_unlock_irqrestore(&nd->queue_lock, flags); >>         return lp; >> > > -- > Tilman Schmidt                    E-Mail: tilman@imap.cc > Bonn, Germany > Diese Nachricht besteht zu 100% aus wiederverwerteten Bits. > Ungeöffnet mindestens haltbar bis: (siehe Rückseite) > > -- 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/