Re: [PATCH 1/3] mm, page_owner: fix off-by-one error in __set_page_owner_handle()

[Kirill A. Shutemov]

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@xxxxxxxxxxxxx>
> Fixes: 7e2f2a0cd17c ("mm, page_owner: record page owner for each subpage")
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov