Re: 2.6.20-mm1 [kernel BUG at mm/swap.c:442]

[James Morris]

On Thu, 15 Feb 2007, Christoph Lameter wrote:

> On Thu, 15 Feb 2007, Andrew Morton wrote:
> 
> > I don't immediately see why that code isn't racy: the page can remain
> > in the pagevec for arbitrary amounts of time and someone can come along
> > and mlock it again.  But given the ease with which you're hitting this,
> > it may not be a race.
> 
> As long as the page is on the pagevec it should be off the LRU. 
> Marking a page PageMlocked requires the page to be on the LRU. So a page 
> cannot be marked PageMlocked as long as it is on the regular pagevecs.
> 
> Somehow a page off the LRU was marked PageMlocked. Or a new anonymous page 
> was allocated and marked PageMlocked and then some later processing put it 
> onto the LRU?
> 
> Maybe try_to_set_mlocked does work some havoc here.
> 
> Could you see if this patch fixes it? This just disabled an optimization 
> to set PageMlocked early.

Nope, doesn't fix the problem.


> Index: linux-2.6.20-mm1/mm/memory.c
> ===================================================================
> --- linux-2.6.20-mm1.orig/mm/memory.c	2007-02-15 14:35:41.000000000 -0800
> +++ linux-2.6.20-mm1/mm/memory.c	2007-02-15 14:35:54.000000000 -0800
> @@ -930,6 +930,8 @@ static void try_to_set_mlocked(struct pa
>  	struct zone *zone;
>  	unsigned long flags;
>  
> +	return;
> +
>  	if (!PageLRU(page) || PageMlocked(page))
>  		return;
>  
> 

-- 
James Morris
<jmorris@xxxxxxxxx>
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