linux-kernel - Re: [PATCH 1/3] mm, page_owner: fix off-by-one error in __set_page_owner

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Date:   Thu, 26 Sep 2019 12:09:35 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Qian Cai <cai@....pw>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH 1/3] mm, page_owner: fix off-by-one error in
 __set_page_owner_handle()

On Wed, Sep 25, 2019 at 04:30:50PM +0200, Vlastimil Babka wrote:
> As noted by Kirill, commit 7e2f2a0cd17c ("mm, page_owner: record page owner for
> each subpage") has introduced an off-by-one error in __set_page_owner_handle()
> when looking up page_ext for subpages. As a result, the head page page_owner
> info is set twice, while for the last tail page, it's not set at all.
> 
> Fix this and also make the code more efficient by advancing the page_ext
> pointer we already have, instead of calling lookup_page_ext() for each subpage.
> Since the full size of struct page_ext is not known at compile time, we can't
> use a simple page_ext++ statement, so introduce a page_ext_next() inline
> function for that.
> 
> Reported-by: Kirill A. Shutemov <kirill@...temov.name>
> Fixes: 7e2f2a0cd17c ("mm, page_owner: record page owner for each subpage")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov