Patch "mm: check if section present during memory block registering" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

mm: check if section present during memory block registering

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-check-if-section-present-during-memory-block-registering.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Yinghai Lu <[email protected]>
Date: Fri, 4 Sep 2015 15:42:39 -0700
Subject: mm: check if section present during memory block registering

From: Yinghai Lu <[email protected]>

commit 04697858d89e4bf2650364f8d6956e2554e8ef88 upstream.

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

  BUG: unable to handle kernel paging request at ffffea0074000020
  IP: 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:
     ? register_mem_sect_under_node+0x66/0xe0
     register_one_node+0x17b/0x240
     ? pci_iommu_alloc+0x6e/0x6e
     topology_init+0x3c/0x95
     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.

The 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 absent section.

---
 drivers/base/node.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -388,6 +388,16 @@ int register_mem_sect_under_node(struct
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
 		int page_nid;
 
+		/*
+		 * memory block could have several absent sections from start.
+		 * skip pfn range from absent section
+		 */
+		if (!pfn_present(pfn)) {
+			pfn = round_down(pfn + PAGES_PER_SECTION,
+					 PAGES_PER_SECTION) - 1;
+			continue;
+		}
+
 		page_nid = get_nid_for_pfn(pfn);
 		if (page_nid < 0)
 			continue;

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/x86-mm-initialize-pmd_idx-in-page_table_range_init_count.patch queue-4.1/mm-check-if-section-present-during-memory-block-registering.patch