Re: [PATCH v1 1/1] mm: buddy page accessed before initialized

[Pavel Tatashin]

On 11/02/2017 09:54 AM, Michal Hocko wrote:
> On Thu 02-11-17 09:39:58, Pavel Tatashin wrote:
> [...]
> > Hi Michal,
> >
> > Previously as before my project? That is because memory for all struct pages
> > was always zeroed in memblock, and in __free_one_page() page_is_buddy() was
> > always returning false, thus we never tried to incorrectly remove it from
> > the list:
> >
> > 837			list_del(&buddy->lru);
> >
> > Now, that memory is not zeroed, page_is_buddy() can return true after kexec
> > when memory is dirty (unfortunately memset(1) with CONFIG_VM_DEBUG does not
> > catch this case). And proceed further to incorrectly remove buddy from the
> > list.
>
> OK, I thought this was a regression from one of the recent patches. So
> the problem is not new. Why don't we see the same problem during the
> standard boot?

Because, I believe, BIOS is zeroing all the memory for us.

> > This is why we must initialize the computed buddy page beforehand.
>
> Ble, this is really ugly. I will think about it more.

Another approach that I considered is to split loop inside 
deferred_init_range() into two loops: one where we initialize pages by 
calling __init_single_page(), another where we free them to buddy 
allocator by calling deferred_free_range().

Pasha