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    DateFri, 13 Jul 2007 14:40:04 +0800
    FromJoe Jin <>
    SubjectRe: [PATCH] Add nid sanity on alloc_pages_node
    On 2007-07-12 22:18, Andrew Morton wrote:
    > On Fri, 13 Jul 2007 10:45:07 +0800 Joe Jin <joe.jin@oracle.com> wrote:
    > 
    > > This patch add nid sanity check on alloc_pages_node().
    > > While two process change nr_hugepages at a system, alloc_fresh_huge_page()
    > > been called, at this function, nid defined as a static variable, but, there
    > > is not any protection of, if 2 process called at the same time, maybe pass a
    > > invalid nid to alloc_pages_node. 
    > > 
    > > We have hit it by following scripts:
    > > 
    > > #!/bin/bash
    > > while : ; do 
    > > 	echo 1000000000000 > /proc/sys/vm/nr_hugepages 
    > > 	echo 1 > /proc/sys/vm/nr_hugepages 
    > > 	echo 10000000000000000000 > /proc/sys/vm/nr_hugepages 
    > > 	echo 0 > /proc/sys/vm/nr_hugepages 
    > > done 
    > > 
    > > 
    > > Run the script at _two_ difference terminal, after a short time, a kernel panic
    > > info will print.
    > > 
    > > 
    > > Signed-off-by: Joe Jin <joe.jin@oracle.com>
    > > ---
    > > 
    > > --- linux-2.6.22/include/linux/gfp.h.orig	2007-07-12 15:06:23.000000000 +0800
    > > +++ linux-2.6.22/include/linux/gfp.h	2007-07-12 15:02:59.000000000 +0800
    > > @@ -133,6 +133,9 @@
    > >  	/* Unknown node is current node */
    > >  	if (nid < 0)
    > >  		nid = numa_node_id();
    > > +	
    > > +	if (unlikely(nid == MAX_NUMNODES))
    > > +		nid = first_node(node_online_map);
    > > 
    > >  	return __alloc_pages(gfp_mask, order,
    > >  		NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask));
    > 
    > alloc_pages_node() is pretty much the last place where we want to fix this:
    > it adds more cycles and more code to many important codepaths in the
    > kernel.
    > 
    > It'd be much better to fix the race within alloc_fresh_huge_page().  That
    > function is pretty pathetic.
    > 
    > Something like this?
    > 
    > --- a/mm/hugetlb.c~a
    > +++ a/mm/hugetlb.c
    > @@ -105,13 +105,20 @@ static void free_huge_page(struct page *
    > 
    >  static int alloc_fresh_huge_page(void)
    >  {
    > -	static int nid = 0;
    > +	static int prev_nid;
    > +	static DEFINE_SPINLOCK(nid_lock);
    >  	struct page *page;
    > -	page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
    > -					HUGETLB_PAGE_ORDER);
    > -	nid = next_node(nid, node_online_map);
    > +	int nid;
    > +
    > +	spin_lock(&nid_lock);
    > +	nid = next_node(prev_nid, node_online_map);
    >  	if (nid == MAX_NUMNODES)
    >  		nid = first_node(node_online_map);
    > +	prev_nid = nid;
    > +	spin_unlock(&nid_lock);
    > +
    > +	page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
    > +					HUGETLB_PAGE_ORDER);
    >  	if (page) {
    >  		set_compound_page_dtor(page, free_huge_page);
    >  		spin_lock(&hugetlb_lock);
    > _
    > 
    
    The patch looks good for this bug, thanks :)
    
    if other caller give a invalid nid to alloc_pages_node(), __alloc_pages
    will crash again.
    
    So I think we add some sanity check for nid at alloc_pages_node is
    meaningful.  
    
    another question, if (nid >= MAX_NUMNODES),  may I set nid to 0 directly
    like following code?
    	if (unlikly(nid >= MAX_NUMNODES)
    		nid = 0
    Thanks,
    Joe
    
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