linux-kernel - Re: [PATCH] mm: fix boundary checking in free_bootmem

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Message-Id: <200803132259.47063.ak@suse.de>
Date:	Thu, 13 Mar 2008 22:59:46 +0100
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Yinghai Lu" <yhlu.kernel@...il.com>, mingo@...e.hu,
	clameter@....com, linux-kernel@...r.kernel.org,
	Yasunori Goto <y-goto@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] mm: fix boundary checking in free_bootmem_core

On Thursday 13 March 2008 02:22:40 Andrew Morton wrote:
> On Wed, 12 Mar 2008 18:11:41 -0700 "Yinghai Lu" <yhlu.kernel@...il.com> wrote:
> 
> > >  <looks at it>
> > >
> > >  Sorry, but I find the changelog very hard to amke sense of.  I presently
> > >  have:
> > >
> > >
> > >   So call it when numa is enabled, we don't know which node have that
> > >   range.  and make it more robust.
> > >
> > >   Try to trim it to get valid sidx, and eidx.
> > >
> > >  Could you please expand on this?
> > 
> > please check following...
> > 
> 
> Heaps better, thanks ;)  Below is what I now have.
> 
> (cc's people)
> 
> Guys, could you please review this?  Maybe test it a bit?
> 
> Thanks.
> 
> 
> From: "Yinghai Lu" <yhlu.kernel@...il.com>
> 
> With numa enabled, some callers could have a range o fmemory on one node but
> try to free that on other node.  This can cause some pages to be freed
> wrongly.

Concrete examples?

If that happens it's really just a problem that the bootmem API
is wrong. I was always annoyed by the hardcoded NODE_DATA(0)s in
free_bootmem. 

I would suggest if that happens you just fix free_bootmem to search
for the correct node instead of hardcoding 0 and then eliminate
free_bootmem_node() everywhere and replace it with free_bootmem()
> 
> For example: when we try to allocate 128g boot ram early for gart/swiotlb, and
> free that range later so gart/swiotlb can get some range afterwards.

I'm confused by the example. AFAIK there is no memory freeing in either
gart nor swiotlb. At least there wasn't until very recently.

> 
> With this patch, we don't need to care which node holds the range, just loop
> to call free_bootmem_node for all online nodes.
> 
> This patch make free_bootmem_core() more robust by trimming the sidx and eidx
> according the ram range that the node has.

I think you should just kill free_bootmem_node() and replace it everywhere
with your improved free_bootmem()


> @@ -125,6 +125,7 @@ static int __init reserve_bootmem_core(b
>  	BUG_ON(!size);
>  	BUG_ON(PFN_DOWN(addr) >= bdata->node_low_pfn);
>  	BUG_ON(PFN_UP(addr + size) > bdata->node_low_pfn);
> +	BUG_ON(addr < bdata->node_boot_start);

That seems unrelated?

>  
>  	sidx = PFN_DOWN(addr - bdata->node_boot_start);
>  	eidx = PFN_UP(addr + size - bdata->node_boot_start);
> @@ -156,21 +157,31 @@ static void __init free_bootmem_core(boo
>  	unsigned long sidx, eidx;
>  	unsigned long i;
>  
> +	BUG_ON(!size);
> +
> +	/* out range */
> +	if (addr + size < bdata->node_boot_start ||
> +		PFN_DOWN(addr) > bdata->node_low_pfn)
> +		return;

I don't really like this silent return without error value.
There should be a BUG() or something for someone passing addresses
outside any node. This check should be probably in the caller.

>  	/*
>  	 * round down end of usable mem, partially free pages are
>  	 * considered reserved.
>  	 */
> -	BUG_ON(!size);
> -	BUG_ON(PFN_DOWN(addr + size) > bdata->node_low_pfn);
>  
> -	if (addr < bdata->last_success)
> +	if (addr >= bdata->node_boot_start && addr < bdata->last_success)
>  		bdata->last_success = addr;
>  
>  	/*
> -	 * Round up the beginning of the address.
> +	 * Round up to index to the range.
>  	 */
> -	sidx = PFN_UP(addr) - PFN_DOWN(bdata->node_boot_start);
> +	if (PFN_UP(addr) > PFN_DOWN(bdata->node_boot_start))
> +		sidx = PFN_UP(addr) - PFN_DOWN(bdata->node_boot_start);
> +	else
> +		sidx = 0;
> +
>  	eidx = PFN_DOWN(addr + size - bdata->node_boot_start);
> +	if (eidx > bdata->node_low_pfn - PFN_DOWN(bdata->node_boot_start))
> +		eidx = bdata->node_low_pfn - PFN_DOWN(bdata->node_boot_start);

I'm not sure for what these other changes are needed?  Just adding the
initial range check should be enough.

If you want to fix something else unrelated please do separate patches.

-Andi

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