Re: [PATCH 3/5] mm: fix show_smap() for zone_device-pmd ranges

[Andrew Morton]

On Tue, 06 Sep 2016 09:49:36 -0700 Dan Williams <dan.j.williams@xxxxxxxxx> wrote:

> Attempting to dump /proc/<pid>/smaps for a process with pmd dax mappings
> currently results in the following VM_BUG_ONs:
> 
>  kernel BUG at mm/huge_memory.c:1105!
>  task: ffff88045f16b140 task.stack: ffff88045be14000
>  RIP: 0010:[<ffffffff81268f9b>]  [<ffffffff81268f9b>] follow_trans_huge_pmd+0x2cb/0x340
>  [..]
>  Call Trace:
>   [<ffffffff81306030>] smaps_pte_range+0xa0/0x4b0
>   [<ffffffff814c2755>] ? vsnprintf+0x255/0x4c0
>   [<ffffffff8123c46e>] __walk_page_range+0x1fe/0x4d0
>   [<ffffffff8123c8a2>] walk_page_vma+0x62/0x80
>   [<ffffffff81307656>] show_smap+0xa6/0x2b0
> 
>  kernel BUG at fs/proc/task_mmu.c:585!
>  RIP: 0010:[<ffffffff81306469>]  [<ffffffff81306469>] smaps_pte_range+0x499/0x4b0
>  Call Trace:
>   [<ffffffff814c2795>] ? vsnprintf+0x255/0x4c0
>   [<ffffffff8123c46e>] __walk_page_range+0x1fe/0x4d0
>   [<ffffffff8123c8a2>] walk_page_vma+0x62/0x80
>   [<ffffffff81307696>] show_smap+0xa6/0x2b0
> 
> These locations are sanity checking page flags that must be set for an
> anonymous transparent huge page, but are not set for the zone_device
> pages associated with dax mappings.

Acked-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>