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

From: Michal Hocko <mhocko@kernel.org>
To: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
	akpm@linux-foundation.org, mgorman@techsingularity.net,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized
Date: Thu, 2 Nov 2017 14:54:23 +0100	[thread overview]
Message-ID: <20171102135423.voxnzk2qkvfgu5l3@dhcp22.suse.cz> (raw)
In-Reply-To: <a9b637b0-2ff0-80e8-76a7-801c5c0820a8@oracle.com>

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?

> This is why we must initialize the computed buddy page beforehand.

Ble, this is really ugly. I will think about it more.
-- 
Michal Hocko
SUSE Labs