Re: [Bugme-new] [Bug 36192] New: Kernel panic when boot the 2.6.39+ kernel based off of 2.6.32 kernel

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 6 Jun 2011 14:45:19 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> Hopefully he can test this one for us as well, thanks.
> 

A  patch with better description (of mine) is here.
Anyway, I felt I needed a fix for ARM special case.

==
fix-init-page_cgroup-for-sparsemem-taking-care-of-broken-page-flags.patch
Even with SPARSEMEM, there are some magical memmap.

If a Node is not aligned to SECTION, memmap of pfn which is out of
Node's range is not initialized. And page->flags contains 0.

If Node(0) doesn't exist, NODE_DATA(pfn_to_nid(pfn)) causes error.

In another case, for example, ARM frees memmap which is never be used
even under SPARSEMEM. In that case, page->flags will contain broken
value.

This patch does a strict check on nid which is obtained by
pfn_to_page() and use proper NID for page_cgroup allocation.

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

---
 mm/page_cgroup.c |   36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

Index: linux-3.0-rc1/mm/page_cgroup.c
===================================================================
--- linux-3.0-rc1.orig/mm/page_cgroup.c
+++ linux-3.0-rc1/mm/page_cgroup.c
@@ -168,6 +168,7 @@ static int __meminit init_section_page_c
 	struct mem_section *section;
 	unsigned long table_size;
 	unsigned long nr;
+	unsigned long tmp;
 	int nid, index;
 
 	nr = pfn_to_section_nr(pfn);
@@ -175,8 +176,41 @@ static int __meminit init_section_page_c
 
 	if (section->page_cgroup)
 		return 0;
+	/*
+	 * check Node-ID. Because we get 'pfn' which is obtained by calculation,
+	 * the pfn may "not exist" or "alreay freed". Even if pfn_valid() returns
+	 * true, page->flags may contain broken value and pfn_to_nid() returns
+	 * bad value.
+	 * (See CONFIG_ARCH_HAS_HOLES_MEMORYMODEL and ARM's free_memmap())
+	 * So, we need to do careful check, here.
+	 */
+	for (tmp = pfn;
+	     tmp < pfn + PAGES_PER_SECTION;
+	     tmp += MAX_ORDER_NR_PAGES, nid = -1) {
+		struct page *page;
+
+		if (!pfn_valid(tmp))
+			continue;
+
+		page = pfn_to_page(tmp);
+		nid = page_to_nid(page);
 
-	nid = page_to_nid(pfn_to_page(pfn));
+		/*
+		 * If 'page' isn't initialized or freed, it may contains broken
+		 * information.
+		 */
+		if (!node_state(nid, N_NORMAL_MEMORY))
+			continue;
+		if (page_to_pfn(pfn_to_page(tmp)) != tmp)
+			continue;
+		/*
+		 * The page seems valid and this 'nid' is safe to access,
+ 		 * at least.
+ 		 */
+		break;
+	}
+	if (nid == -1)
+		return 0;
 	table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
 	base = alloc_page_cgroup(table_size, nid);
 

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