On Fri, Jul 13, 2018 at 4:51 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I'm building a "replace VM_BUG_ON() with proper printk's instead" right now.
Ok, the machine now stays up, and I get messages like
Removed VM_BUG_ON()!
pfn c2400 - c25ff
zone DMA32 DMA
zone pfn 1000 1
Removed VM_BUG_ON()!
pfn c0a00 - c0bff
zone DMA32 DMA
zone pfn 1000 1
Removed VM_BUG_ON()!
pfn c2200 - c23ff
zone DMA DMA32
zone pfn 1 1000
instead.
That's from
+ printk("Removed VM_BUG_ON()!\n");
+ printk(" pfn %lx - %lx\n", page_to_pfn(start_page),
page_to_pfn(end_page));
+ printk(" zone %s %s\n", page_zone(start_page)->name,
page_zone(end_page)->name);
+ printk(" zone pfn %lx %lx\n",
page_zone(start_page)->zone_start_pfn,
page_zone(end_page)->zone_start_pfn);
inside an if() statement that replaced that VM_BUG_ON().
WTF? That's just odd.
But everything seems to work fine, and now it doesn't crash.
But there's something really odd going on wrt page_zone() and/or page_to_pfn().
page_to_pfn() implies this is just regular memory in the 3GB area. It
is likely related to this:
BIOS-e820: [mem 0x00000000c0b33000-0x00000000c226cfff] reserved
BIOS-e820: [mem 0x00000000c226d000-0x00000000c227efff] ACPI data
BIOS-e820: [mem 0x00000000c227f000-0x00000000c2439fff] usable
BIOS-e820: [mem 0x00000000c243a000-0x00000000c2a61fff] ACPI NVS
BIOS-e820: [mem 0x00000000c2a62000-0x00000000c32fefff] reserved
BIOS-e820: [mem 0x00000000c32ff000-0x00000000c32fffff] usable
BIOS-e820: [mem 0x00000000c3300000-0x00000000c7ffffff] reserved
I dunno. It's a bit odd. I'm not sure I understand that VM_BUG_ON().
Adding Ard (who worked on the memblock_next_valid_pfn() thing not that
long ago) and must have hit this same BUG_ON() because he modified it
not that long ago.
Ard, I triggered the VM_BUG_ON() in mm/page_alloc.c:2016, with a call trace opf
RIP: move_pfreepages_block()
Call Trace:
steal_suitable_fallback
get_page_from_freelist
...
just for some context.
Linus
