linux-kernel - Re: lockdep complaints in slab allocator

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Message-ID: <84144f020911241259r3a604b29yb59902655ec03a20@mail.gmail.com>
Date:	Tue, 24 Nov 2009 22:59:44 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
	cl@...ux-foundation.org, mpm@...enic.com,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: lockdep complaints in slab allocator

On Tue, Nov 24, 2009 at 6:23 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Mon, Nov 23, 2009 at 09:00:00PM +0200, Pekka Enberg wrote:
>> Hi Peter,
>>
>> On Fri, 2009-11-20 at 16:09 +0100, Peter Zijlstra wrote:
>> > > 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?
>> >
>> > You'd have to somehow push the nested state down from the
>> > kmem_cache_free() call in slab_destroy() to all nc->lock sites below.
>>
>> That turns out to be _very_ hard. How about something like the following
>> untested patch which delays slab_destroy() while we're under nc->lock.
>>
>>                       Pekka
>
> Preliminary tests look good!  The test was a ten-hour rcutorture run on
> an 8-CPU Power system with a half-second delay between randomly chosen
> CPU-hotplug operations.  No lockdep warnings.  ;-)
>
> Will keep hammering on it.

Thanks! Please let me know when you're hammered it enough :-). Peter,
may I have your ACK or NAK on the patch, please?
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