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

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Date:	Tue, 18 Jun 2013 12:21:33 +0400
From:	Glauber Costa <glommer@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 Tue, Jun 18, 2013 at 10:19:31AM +0200, Michal Hocko wrote:
> On Tue 18-06-13 02:30:05, Glauber Costa wrote:
> > On Mon, Jun 17, 2013 at 02:35:08PM -0700, Andrew Morton wrote:
> [...]
> > > The trace says shrink_slab_node->super_cache_scan->prune_icache_sb.  So
> > > it's inodes?
> > > 
> > Assuming there is no memory corruption of any sort going on , let's
> > check the code. nr_item is only manipulated in 3 places:
> > 
> > 1) list_lru_add, where it is increased
> > 2) list_lru_del, where it is decreased in case the user have voluntarily removed the
> >    element from the list
> > 3) list_lru_walk_node, where an element is removing during shrink.
> > 
> > All three excerpts seem to be correctly locked, so something like this
> > indicates an imbalance.  Either the element was never added to the
> > list, or it was added, removed, and we didn't notice it. (Again, your
> > backing storage is not XFS, is it? If it is , we have another user to
> > look for)
> 
> No this is ext3. But I can try to test with xfs as well if it helps.
> [...]

XFS won't help this, on the contrary. The reason I asked is because XFS
uses list_lru for its internal structures as well. So it is actually preferred
if you are reproducing this without it, so we can at least isolate that part.
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