From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757209Ab0JLK1W (ORCPT ); Tue, 12 Oct 2010 06:27:22 -0400 Received: from casper.infradead.org ([85.118.1.10]:44089 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756888Ab0JLK1U convert rfc822-to-8bit (ORCPT ); Tue, 12 Oct 2010 06:27:20 -0400 Subject: Re: [PATCH 1/2] lockdep: check the depth of subclass From: Peter Zijlstra To: Hitoshi Mitake Cc: Ingo Molnar , linux-kernel@vger.kernel.org, h.mitake@gmail.com, Dmitry Torokhov , Vojtech Pavlik , Frederic Weisbecker In-Reply-To: <1286269311-28336-1-git-send-email-mitake@dcl.info.waseda.ac.jp> References: <1286269311-28336-1-git-send-email-mitake@dcl.info.waseda.ac.jp> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 12 Oct 2010 12:27:01 +0200 Message-ID: <1286879221.29097.39.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2010-10-05 at 18:01 +0900, Hitoshi Mitake wrote: > Current look_up_lock_class() doesn't check the parameter "subclass". > This rarely rises problems because the main caller of this function, > register_lock_class(), checks it. > But register_lock_class() is not the only function which calls > look_up_lock_class(). lock_set_class() and its callees also call it. > And lock_set_class() doesn't check this parameter. > > This will rise problems when the the value of subclass is larger > MAX_LOCKDEP_SUBCLASSES. Because the address (used as the key of class) > caliculated with too large subclass has a possibility to point > another key in different lock_class_key. > Of course this problem depends on the memory layout and > occurs with really low possibility. > > And mousedev_create() calles lockdep_set_subclass() and > sets class of mousedev->mutex as MOUSEDEV_MIX(== 31). > And if my understanding is correct, > this subclass doesn't have to be MOUSEDEV_MIX, > so I modified this value to SINGLE_DEPTH_NESTING. > > Signed-off-by: Hitoshi Mitake > Cc: Dmitry Torokhov > Cc: Vojtech Pavlik > Cc: Peter Zijlstra > Cc: Frederic Weisbecker > --- > drivers/input/mousedev.c | 2 +- > kernel/lockdep.c | 15 +++++++++++++++ > 2 files changed, 16 insertions(+), 1 deletions(-) > > diff --git a/drivers/input/mousedev.c b/drivers/input/mousedev.c > index d528a2d..9897334 100644 > --- a/drivers/input/mousedev.c > +++ b/drivers/input/mousedev.c > @@ -866,7 +866,7 @@ static struct mousedev *mousedev_create(struct input_dev *dev, > spin_lock_init(&mousedev->client_lock); > mutex_init(&mousedev->mutex); > lockdep_set_subclass(&mousedev->mutex, > - minor == MOUSEDEV_MIX ? MOUSEDEV_MIX : 0); > + minor == MOUSEDEV_MIX ? SINGLE_DEPTH_NESTING : 0); Ah good find. > init_waitqueue_head(&mousedev->wait); > > if (minor == MOUSEDEV_MIX) > diff --git a/kernel/lockdep.c b/kernel/lockdep.c > index 84baa71..c4c13ae 100644 > --- a/kernel/lockdep.c > +++ b/kernel/lockdep.c > @@ -639,6 +639,21 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass) > } > #endif > > + if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) { > + /* > + * This check should be done not only in __lock_acquire() > + * but also here. Because register_lock_class() is also called > + * by lock_set_class(). Callers of lock_set_class() can > + * pass invalid value as subclass. > + */ > + > + debug_locks_off(); > + printk(KERN_ERR "BUG: looking up invalid subclass: %u\n", subclass); > + printk(KERN_ERR "turning off the locking correctness validator.\n"); > + dump_stack(); > + return NULL; > + } Would we catch all cases if we moved this check from __lock_acquire() into register_lock_class()? It would result in only a single instance of this logic. > /* > * Static locks do not have their class-keys yet - for them the key > * is the lock object itself: