On Wed, 26 Aug 2015, Yinghai Lu wrote:
> 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 absent section.
>
> Reported-by: Tony Luck <tony.luck@xxxxxxxxx>
> Tested-by: Tony Luck <tony.luck@xxxxxxxxx>
> Fixes: bdee237c0343 ("x86: mm: Use 2GB memory block size on large memory x86-64 systems")
> Fixes: 982792c782ef ("x86, mm: probe memory block size for generic x86 64bit")
> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx #v3.15
stable@xxxxxxxxxxxxxxx probably never received this since it was sent to
stable@xxxxxxxxxxxxxxx.#v3.15
> Index: linux-2.6/drivers/base/node.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/node.c
> +++ linux-2.6/drivers/base/node.c
> @@ -390,7 +390,18 @@ int register_mem_sect_under_node(struct
> 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;
> +
> + /*
> + * memory block could have several absent sections from start.
> + * skip pfn range from absent section
> + */
> + 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)
scn_nr should really be unsigned long, but it would probably be better to
simply use if (!pfn_present(pfn)) rather than store the section number.
\
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