linux-kernel - Re: lockdep complaints in slab allocator

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Message-ID: <20091124214740.GJ6831@linux.vnet.ibm.com>
Date:	Tue, 24 Nov 2009 13:47:40 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
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 10:59:44PM +0200, Pekka Enberg wrote:
> 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?

I expect to hammer it over the USA Thanksgiving holiday Thu-Sun this week.
It is like this, Pekka: since I don't drink, it is instead your code
that is going to get hammered this weekend!

							Thanx, Paul
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