linux-kernel - Re: linux-next: slab shrinkers: BUG at mm/list

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Date:	Mon, 17 Jun 2013 14:35:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...il.com>
Cc:	Michal Hocko <mhocko@...e.cz>, Dave Chinner <david@...morbit.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: slab shrinkers: BUG at mm/list_lru.c:92

On Mon, 17 Jun 2013 19:14:12 +0400 Glauber Costa <glommer@...il.com> wrote:

> > I managed to trigger:
> > [ 1015.776029] kernel BUG at mm/list_lru.c:92!
> > [ 1015.776029] invalid opcode: 0000 [#1] SMP
> > with Linux next (next-20130607) with https://lkml.org/lkml/2013/6/17/203
> > on top. 
> > 
> > This is obviously BUG_ON(nlru->nr_items < 0) and 
> > ffffffff81122d0b:       48 85 c0                test   %rax,%rax
> > ffffffff81122d0e:       49 89 44 24 18          mov    %rax,0x18(%r12)
> > ffffffff81122d13:       0f 84 87 00 00 00       je     ffffffff81122da0 <list_lru_walk_node+0x110>
> > ffffffff81122d19:       49 83 7c 24 18 00       cmpq   $0x0,0x18(%r12)
> > ffffffff81122d1f:       78 7b                   js     ffffffff81122d9c <list_lru_walk_node+0x10c>
> > [...]
> > ffffffff81122d9c:       0f 0b                   ud2
> > 
> > RAX is -1UL.
> Yes, fearing those kind of imbalances, we decided to leave the counter as a signed quantity
> and BUG, instead of an unsigned quantity.
> 
> > 
> > I assume that the current backtrace is of no use and it would most
> > probably be some shrinker which doesn't behave.
> > 
> There are currently 3 users of list_lru in tree: dentries, inodes and xfs.
> Assuming you are not using xfs, we are left with dentries and inodes.
> 
> The first thing to do is to find which one of them is misbehaving. You can try finding
> this out by the address of the list_lru, and where it lays in the superblock.
> 
> Once we know each of them is misbehaving, then we'll have to figure out why.

The trace says shrink_slab_node->super_cache_scan->prune_icache_sb.  So
it's inodes?

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