From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id D2CF76B00BF for ; Fri, 20 Nov 2009 09:49:03 -0500 (EST) Received: from d01relay03.pok.ibm.com (d01relay03.pok.ibm.com [9.56.227.235]) by e5.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id nAKEcAnE025266 for ; Fri, 20 Nov 2009 09:38:10 -0500 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay03.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nAKEmun9090444 for ; Fri, 20 Nov 2009 09:48:56 -0500 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nAKEmtQ4032257 for ; Fri, 20 Nov 2009 09:48:56 -0500 Date: Fri, 20 Nov 2009 06:48:55 -0800 From: "Paul E. McKenney" Subject: Re: lockdep complaints in slab allocator Message-ID: <20091120144855.GB22527@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20091118181202.GA12180@linux.vnet.ibm.com> <84144f020911192249l6c7fa495t1a05294c8f5b6ac8@mail.gmail.com> <1258709153.11284.429.camel@laptop> <84144f020911200238w3d3ecb38k92ca595beee31de5@mail.gmail.com> <1258714328.11284.522.camel@laptop> <4B067816.6070304@cs.helsinki.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B067816.6070304@cs.helsinki.fi> Sender: owner-linux-mm@kvack.org To: Pekka Enberg Cc: Peter Zijlstra , linux-mm@kvack.org, cl@linux-foundation.org, mpm@selenic.com, LKML , Nick Piggin List-ID: On Fri, Nov 20, 2009 at 01:05:58PM +0200, Pekka Enberg wrote: > Peter Zijlstra kirjoitti: >> On Fri, 2009-11-20 at 12:38 +0200, Pekka Enberg wrote: >>> >>> On Fri, Nov 20, 2009 at 11:25 AM, Peter Zijlstra >>> wrote: >>>> 2) propagate the nesting information and user spin_lock_nested(), given >>>> that slab is already a rat's nest, this won't make it any less obvious. >>> spin_lock_nested() doesn't really help us here because there's a >>> _real_ possibility of a recursive spin lock here, right? >> Well, I was working under the assumption that your analysis of it being >> a false positive was right ;-) >> I briefly tried to verify that, but got lost and gave up, at which point >> I started looking for ways to annotate. > > Uh, ok, so apparently I was right after all. There's a comment in > free_block() above the slab_destroy() call that refers to the comment above > alloc_slabmgmt() function definition which explains it all. > > Long story short: ->slab_cachep never points to the same kmalloc cache > we're allocating or freeing from. Where do we need to put the > spin_lock_nested() annotation? Would it be enough to just use it in > cache_free_alien() for alien->lock or do we need it in cache_flusharray() > as well? Hmmm... If the nc->lock spinlocks are always from different slabs (as alloc_slabmgmt()'s block comment claims), why not just give each array_cache structure's lock its own struct lock_class_key? They are zero size unless you have lockdep enabled. Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org