Re: Instability in current -git tree

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 14 July 2018 at 08:20, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Fri, Jul 13, 2018 at 4:51 PM Linus Torvalds
> <torvalds@linux-foundation.org> 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.
>

Pavel's fix for this issue in commit e181ae0c5db9 is causing boot
problems on i686 for me.

Is anyone else seeing the same?

I get no output whatsoever when booting a i386_defconfig kernel under
qemu/kvm (without EFI)