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

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Date:	Sun, 23 Jun 2013 15:55:20 +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 Sun, Jun 23, 2013 at 03:51:29PM +0400, Glauber Costa wrote:
> On Fri, Jun 21, 2013 at 11:00:21AM +0200, Michal Hocko wrote:
> > On Thu 20-06-13 17:12:01, Michal Hocko wrote:
> > > I am bisecting it again. It is quite tedious, though, because good case
> > > is hard to be sure about.
> > 
> > OK, so now I converged to 2d4fc052 (inode: convert inode lru list to generic lru
> > list code.) in my tree and I have double checked it matches what is in
> > the linux-next. This doesn't help much to pin point the issue I am
> > afraid :/
> > 
> Can you revert this patch (easiest way ATM is to rewind your tree to a point
> right before it) and apply the following patch?
> 
> As Dave has mentioned, it is very likely that this bug was already there, we
> were just not ever checking imbalances. The attached patch would tell us at
> least if the imbalance was there before. If this is the case, I would suggest
> turning the BUG condition into a WARN_ON_ONCE since we would be officially
> not introducing any regression. It is no less of a bug, though, and we should
> keep looking for it.
> 
> The main change from before / after the patch is that we are now keeping things
> per node. One possibility of having this BUGing would be to have an inode to be
> inserted into one node-lru and removed from another. I cannot see how it could
> happen, because kernel pages are stable in memory and are not moved from node
> to node. We could still have some sort of weird bug in the node calculation
> function. In any case, would it be possible for you to artificially restrict
> your setup to a single node ? Although I have no idea how to do that, we seem
> to have no parameter to disable numa. Maybe booting with less memory, enough to
> fit a single node?
> 
The patch:

View attachment "BUG.patch" of type "text/plain" (920 bytes)