[PATCH] mm: Check if section present during memory block (un)registering

[Yinghai Lu <yinghai@kernel.org>]

Tony found on his setup, if memory block size 512M will cause crash
during booting.

 BUG: unable to handle kernel paging request at ffffea0074000020
 IP: [<ffffffff81670527>] get_nid_for_pfn+0x17/0x40
 PGD 128ffcb067 PUD 128ffc9067 PMD 0 
 Oops: 0000 [#1] SMP 
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc8 #1
...
 Call Trace:
  [<ffffffff81453b56>] ? register_mem_sect_under_node+0x66/0xe0
  [<ffffffff81453eeb>] register_one_node+0x17b/0x240
  [<ffffffff81b1f1ed>] ? pci_iommu_alloc+0x6e/0x6e
  [<ffffffff81b1f229>] topology_init+0x3c/0x95
  [<ffffffff8100213d>] do_one_initcall+0xcd/0x1f0

The system has non continuous RAM address:
 BIOS-e820: [mem 0x0000001300000000-0x0000001cffffffff] usable
 BIOS-e820: [mem 0x0000001d70000000-0x0000001ec7ffefff] usable
 BIOS-e820: [mem 0x0000001f00000000-0x0000002bffffffff] usable
 BIOS-e820: [mem 0x0000002c18000000-0x0000002d6fffefff] usable
 BIOS-e820: [mem 0x0000002e00000000-0x00000039ffffffff] usable

So there are start sections in memory block not present.
For example:
memory block : [0x2c18000000, 0x2c20000000) 512M
first three sections are not present.

Current register_mem_sect_under_node() assume first section is present,
but memory block section number range [start_section_nr, end_section_nr]
would include not present section.

For arch that support vmemmap, we don't setup memmap for struct page area
within not present sections area.

So skip the pfn range that belong to not present section.

Als fixes unregister_mem_sect_under_nodes().

Reported-by: Tony Luck <tony.luck@intel.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 31df474d..cc910ad 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -390,8 +390,14 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
 	sect_end_pfn += PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int page_nid;
+		int page_nid, scn_nr;
 
+		scn_nr = pfn_to_section_nr(pfn);
+		if (!present_section_nr(scn_nr)) {
+			pfn = round_down(pfn + PAGES_PER_SECTION,
+					 PAGES_PER_SECTION) - 1;
+			continue;
+		}
 		page_nid = get_nid_for_pfn(pfn);
 		if (page_nid < 0)
 			continue;
@@ -426,10 +432,18 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
 		return -ENOMEM;
 	nodes_clear(*unlinked_nodes);
 
-	sect_start_pfn = section_nr_to_pfn(phys_index);
-	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
+	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
+	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
+	sect_end_pfn += PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int nid;
+		int nid, scn_nr;
+
+		scn_nr = pfn_to_section_nr(pfn);
+		if (!present_section_nr(scn_nr)) {
+			pfn = round_down(pfn + PAGES_PER_SECTION,
+					 PAGES_PER_SECTION) - 1;
+			continue;
+		}
 
 		nid = get_nid_for_pfn(pfn);
 		if (nid < 0)