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Subject: Re: kernel BUG at mm/slqb.c:1411!
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>, linux-mm <linux-mm@kvack.org>,
       LKML <linux-kernel@vger.kernel.org>, Nick Piggin <npiggin@suse.de>,
       matthew.r.wilcox@intel.com
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Date: Fri, 15 May 2009 11:08:51 +0300
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Hi Motohiro-san,

On Wed, 2009-05-13 at 17:37 +0900, Minchan Kim wrote:
> > > > On Wed, 13 May 2009 16:42:37 +0900 (JST)
> > > > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> > > > 
> > > > Hmm. I don't know slqb well.
> > > > So, It's just my guess. 
> > > > 
> > > > We surely increase l->nr_partial in  __slab_alloc_page.
> > > > In between l->nr_partial++ and call __cache_list_get_page, Who is decrease l->nr_partial again.
> > > > After all, __cache_list_get_page return NULL and hit the VM_BUG_ON.
> > > > 
> > > > Comment said :
> > > > 
> > > >         /* Protects nr_partial, nr_slabs, and partial */
> > > >   spinlock_t    page_lock;
> > > > 
> > > > As comment is right, We have to hold the l->page_lock ?
> > > 
> > > Makes sense. Nick? Motohiro-san, can you try this patch please?
> > 
> > This issue is very rarely. please give me one night.

On Fri, 2009-05-15 at 08:38 +0900, KOSAKI Motohiro wrote:
> -ENOTREPRODUCED
> 
> I guess your patch is right fix. thanks!

Thank you so much for testing!

Nick seems to have gone silent for the past few days so I went ahead and
merged the patch.

Did you have CONFIG_PROVE_LOCKING enabled, btw? I think I got the lock
order correct but I don't have a NUMA machine to test it with here.

			Pekka