Re: [memcg BUG] unable to handle kernel NULL pointer derefence at 00000000

KAMEZAWA Hiroyuki
2008-10-21T08:58:02Z

On Tue, 21 Oct 2008 16:35:09 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Tue, 21 Oct 2008 15:21:07 +0800
> > Li Zefan <lizf@cn.fujitsu.com> wrote:
> >> dmesg is attached.
> >>
> > Thanks....I think I caught some. (added Mel Gorman to CC:)
> >
> > NODE_DATA(nid)->spanned_pages just means sum of zone->spanned_pages in node.
> >
> > So, If there is a hole between zone, node->spanned_pages doesn't mean
> > length of node's memmap....(then, some hole can be skipped.)
> >
> > OMG....Could you try this ?
> >
>
> No luck, the same bug still exists. :(
>
This is a little fixed one..

please..
-Kame
==
NODE_DATA(nid)->node_spanned_pages doesn't means width of node's memory.

alloc_node_page_cgroup() misunderstand it. This patch tries to use
the same algorithm as alloc_node_mem_map() for allocating page_cgroup()
for node.

Changelog:
- fixed range of initialization loop.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

mm/page_cgroup.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

Index: linux-2.6.27/mm/page_cgroup.c
===================================================================
--- linux-2.6.27.orig/mm/page_cgroup.c
+++ linux-2.6.27/mm/page_cgroup.c
@@ -9,6 +9,8 @@
static void __meminit
__init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
{
+ if (!pfn_valid(pfn))
+ return;
pc->flags = 0;
pc->mem_cgroup = NULL;
pc->page = pfn_to_page(pfn);
@@ -41,10 +43,18 @@ static int __init alloc_node_page_cgroup
{
struct page_cgroup *base, *pc;
unsigned long table_size;
- unsigned long start_pfn, nr_pages, index;
+ unsigned long start, end, start_pfn, nr_pages, index;

+ /*
+ * Instead of allocating page_cgroup for [start, end)
+ * We allocate page_cgroup to the same size of mem_map.
+ * See page_alloc.c::alloc_node_mem_map()
+ */
start_pfn = NODE_DATA(nid)->node_start_pfn;
- nr_pages = NODE_DATA(nid)->node_spanned_pages;
+ start = start_pfn & ~(MAX_ORDER_NR_PAGES - 1);
+ end = start_pfn + NODE_DATA(nid)->node_spanned_pages;
+ end = ALIGN(end, MAX_ORDER_NR_PAGES);
+ nr_pages = end - start;

table_size = sizeof(struct page_cgroup) * nr_pages;

@@ -52,11 +62,12 @@ static int __init alloc_node_page_cgroup
table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
if (!base)
return -ENOMEM;
+
for (index = 0; index < nr_pages; index++) {
pc = base + index;
- __init_page_cgroup(pc, start_pfn + index);
+ __init_page_cgroup(pc, start + index);
}
- NODE_DATA(nid)->node_page_cgroup = base;
+ NODE_DATA(nid)->node_page_cgroup = base + start_pfn - start;
total_usage += table_size;
return 0;
}