Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753284AbYCLU1W (ORCPT ); Wed, 12 Mar 2008 16:27:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751844AbYCLU1N (ORCPT ); Wed, 12 Mar 2008 16:27:13 -0400 Received: from e28smtp06.in.ibm.com ([59.145.155.6]:51019 "EHLO e28esmtp06.in.ibm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751936AbYCLU1M (ORCPT ); Wed, 12 Mar 2008 16:27:12 -0400 Date: Thu, 13 Mar 2008 01:56:58 +0530 From: Gautham R Shenoy To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Hugh Dickins Subject: Re: [PATCH 1/2] lockdep: fix recursive read lock validation Message-ID: <20080312202658.GA7856@in.ibm.com> Reply-To: ego@in.ibm.com References: <20080312120920.929901000@chello.nl> <20080312121323.697634000@chello.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080312121323.697634000@chello.nl> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3271 Lines: 89 On Wed, Mar 12, 2008 at 01:09:21PM +0100, Peter Zijlstra wrote: > __lock_acquire( .read = 2 ) > hlock->read = read; /* [1] */ > validate_chain() > ret = check_deadlock(); /* returns 2 when recursive */ > > if (ret == 2) > hlock->read = 2; /* but it was already 2 from [1] */ > > check_prevs_add() > if (hlock->read != 2) > /* add to dependency chain */ > > So it will never add a recursive read lock to the dependency chain. Fix this > by setting hlock->read to 1 when its the first recursive lock instance. > > This means that the following sequence is now invalid, whereas previously > it was considered valid: > > rlock(a); rlock(b); runlock(b); runlock(a) > rlock(b); rlock(a); > > It really is invalid when considered against write locks. > > Signed-off-by: Peter Zijlstra > CC: Gautham R Shenoy Tested-by: Gautham R Shenoy > --- > kernel/lockdep.c | 9 ++++----- > lib/locking-selftest.c | 12 ++++++------ > 2 files changed, 10 insertions(+), 11 deletions(-) > > Index: linux-2.6-2/kernel/lockdep.c > =================================================================== > --- linux-2.6-2.orig/kernel/lockdep.c > +++ linux-2.6-2/kernel/lockdep.c > @@ -1557,12 +1557,11 @@ static int validate_chain(struct task_st > if (!ret) > return 0; > /* > - * Mark recursive read, as we jump over it when > - * building dependencies (just like we jump over > - * trylock entries): > + * If we are the first recursive read, don't jump over our > + * dependency. > */ > - if (ret == 2) > - hlock->read = 2; > + if (hlock->read == 2 && ret != 2) > + hlock->read = 1; > /* > * Add dependency only if this lock is not the head > * of the chain, and if it's not a secondary read-lock: > Index: linux-2.6-2/lib/locking-selftest.c > =================================================================== > --- linux-2.6-2.orig/lib/locking-selftest.c > +++ linux-2.6-2/lib/locking-selftest.c > @@ -1135,12 +1135,12 @@ void locking_selftest(void) > debug_locks_silent = !debug_locks_verbose; > > DO_TESTCASE_6R("A-A deadlock", AA); > - DO_TESTCASE_6R("A-B-B-A deadlock", ABBA); > - DO_TESTCASE_6R("A-B-B-C-C-A deadlock", ABBCCA); > - DO_TESTCASE_6R("A-B-C-A-B-C deadlock", ABCABC); > - DO_TESTCASE_6R("A-B-B-C-C-D-D-A deadlock", ABBCCDDA); > - DO_TESTCASE_6R("A-B-C-D-B-D-D-A deadlock", ABCDBDDA); > - DO_TESTCASE_6R("A-B-C-D-B-C-D-A deadlock", ABCDBCDA); > + DO_TESTCASE_6("A-B-B-A deadlock", ABBA); > + DO_TESTCASE_6("A-B-B-C-C-A deadlock", ABBCCA); > + DO_TESTCASE_6("A-B-C-A-B-C deadlock", ABCABC); > + DO_TESTCASE_6("A-B-B-C-C-D-D-A deadlock", ABBCCDDA); > + DO_TESTCASE_6("A-B-C-D-B-D-D-A deadlock", ABCDBDDA); > + DO_TESTCASE_6("A-B-C-D-B-C-D-A deadlock", ABCDBCDA); > DO_TESTCASE_6("double unlock", double_unlock); > DO_TESTCASE_6("initialize held", init_held); > DO_TESTCASE_6_SUCCESS("bad unlock order", bad_unlock_order); > > -- -- Thanks and Regards gautham -- 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/