From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 042006B00B9 for ; Fri, 20 Nov 2009 06:06:00 -0500 (EST) Message-ID: <4B067816.6070304@cs.helsinki.fi> Date: Fri, 20 Nov 2009 13:05:58 +0200 From: Pekka Enberg MIME-Version: 1.0 Subject: Re: lockdep complaints in slab allocator 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> In-Reply-To: <1258714328.11284.522.camel@laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: paulmck@linux.vnet.ibm.com, linux-mm@kvack.org, cl@linux-foundation.org, mpm@selenic.com, LKML , Nick Piggin List-ID: 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? Pekka -- 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