Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756531AbYH2ASS (ORCPT ); Thu, 28 Aug 2008 20:18:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754187AbYH2ASA (ORCPT ); Thu, 28 Aug 2008 20:18:00 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57952 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753829AbYH2AR7 (ORCPT ); Thu, 28 Aug 2008 20:17:59 -0400 Date: Thu, 28 Aug 2008 17:17:06 -0700 From: Andrew Morton To: Vegard Nossum Cc: mingo@elte.hu, daniel.blueman@gmail.com, tglx@linutronix.de, clameter@sgi.com, torvalds@linux-foundation.org, rjw@sisk.pl, linux-kernel@vger.kernel.org, bunk@kernel.org, protasnb@gmail.com, kernel-testers@vger.kernel.org Subject: Re: [PATCH] debugobjects: fix lockdep warning #2 Message-Id: <20080828171706.6080accf.akpm@linux-foundation.org> In-Reply-To: <20080828153214.GA27653@localhost.localdomain> References: <20080828153214.GA27653@localhost.localdomain> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5067 Lines: 146 On Thu, 28 Aug 2008 17:32:14 +0200 Vegard Nossum wrote: > On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar wrote: > > could you resend the final patch please? It's a candidate for .27, if it > > works out fine. > > Here is the combined patch. I've tested it only briefly, and I am > unsure of whether it still produces lockdep warnings for Daniel or > not. I wish it would not be applied anywhere unless it was > officially Reviewed-by: someone. In particular, I'm not quite > steady with the irq-safe locking (Thomas might want to have a look). > It all looks good to me. > > > >From 977cf583b79be7308d5e310711fe6038c8af96a4 Mon Sep 17 00:00:00 2001 > From: Vegard Nossum > Date: Thu, 28 Aug 2008 17:09:57 +0200 > Subject: [PATCH] debugobjects: fix lockdep warning #2 > > Daniel J. Blueman reported: > > ======================================================= > > [ INFO: possible circular locking dependency detected ] > > 2.6.27-rc4-224c #1 > > ------------------------------------------------------- > > hald/4680 is trying to acquire lock: > > (&n->list_lock){++..}, at: [] add_partial+0x26/0x80 > > > > but task is already holding lock: > > (&obj_hash[i].lock){++..}, at: [] > > debug_object_free+0x5c/0x120 > > We fix it by moving the actual freeing to outside the lock (the lock > now only protects the list). > > The lock is also promoted to irq-safe (suggested by Dan). What was the reason for this other change? I'm sure Dan is a fine chap, but we usually prefer a little more justification for changes ;) > Reported-by: Daniel J Blueman > Signed-off-by: Vegard Nossum > --- > lib/debugobjects.c | 38 +++++++++++++++++++++++++++++--------- > 1 files changed, 29 insertions(+), 9 deletions(-) > > diff --git a/lib/debugobjects.c b/lib/debugobjects.c > index 19acf8c..acf9ed8 100644 > --- a/lib/debugobjects.c > +++ b/lib/debugobjects.c > @@ -115,9 +115,10 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b) > static struct debug_obj * > alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr) > { > + unsigned long flags; > struct debug_obj *obj = NULL; > > - spin_lock(&pool_lock); > + spin_lock_irqsave(&pool_lock, flags); > if (obj_pool.first) { > obj = hlist_entry(obj_pool.first, typeof(*obj), node); > > @@ -136,7 +137,7 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr) > if (obj_pool_free < obj_pool_min_free) > obj_pool_min_free = obj_pool_free; > } > - spin_unlock(&pool_lock); > + spin_unlock_irqrestore(&pool_lock, flags); > > return obj; > } > @@ -146,18 +147,19 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr) > */ > static void free_object(struct debug_obj *obj) > { > + unsigned long flags; > unsigned long idx = (unsigned long)(obj - obj_static_pool); > > if (obj_pool_free < ODEBUG_POOL_SIZE || idx < ODEBUG_POOL_SIZE) { > - spin_lock(&pool_lock); > + spin_lock_irqsave(&pool_lock, flags); > hlist_add_head(&obj->node, &obj_pool); > obj_pool_free++; > obj_pool_used--; > - spin_unlock(&pool_lock); > + spin_unlock_irqrestore(&pool_lock, flags); > } else { > - spin_lock(&pool_lock); > + spin_lock_irqsave(&pool_lock, flags); > obj_pool_used--; > - spin_unlock(&pool_lock); > + spin_unlock_irqrestore(&pool_lock, flags); > kmem_cache_free(obj_cache, obj); > } > } > @@ -170,19 +172,28 @@ static void debug_objects_oom(void) > { > struct debug_bucket *db = obj_hash; > struct hlist_node *node, *tmp; > + HLIST_HEAD(freelist); > struct debug_obj *obj; > unsigned long flags; > int i; > > printk(KERN_WARNING "ODEBUG: Out of memory. ODEBUG disabled\n"); > > + /* XXX: Could probably be optimized by transplantation of more than > + * one entry at a time. */ > for (i = 0; i < ODEBUG_HASH_SIZE; i++, db++) { > spin_lock_irqsave(&db->lock, flags); > hlist_for_each_entry_safe(obj, node, tmp, &db->list, node) { > hlist_del(&obj->node); > - free_object(obj); > + hlist_add_head(&obj->node, &freelist); > } > spin_unlock_irqrestore(&db->lock, flags); > + > + /* Now free them */ > + hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) { > + hlist_del(&obj->node); > + free_object(obj); I suspect that we can avoid the hlist_del() here, perhaps with a little effort. > + > + /* Now free them */ > + hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) { > + hlist_del(&obj->node); > + free_object(obj); > + } > + and the other one. But I'm not sure that it's worth putting effort into - leaving dead objects strung onto a partially-live list is a little bit smelly IMO. -- 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/