linux-kernel - Re: [PATCH] mm: fix potential pte_unmap

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Date:   Fri, 16 Oct 2020 15:11:12 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     osalvador@...e.de
Cc:     Shijie Luo <luoshijie1@...wei.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linmiaohe@...wei.com, linfeilong@...wei.com
Subject: Re: [PATCH] mm: fix potential pte_unmap_unlock pte error

On Fri 16-10-20 14:37:08, osalvador@...e.de wrote:
> On 2020-10-16 14:31, Michal Hocko wrote:
> > I do not like the fix though. The code is really confusing. Why should
> > we check for flags in each iteration of the loop when it cannot change?
> > Also why should we take the ptl lock in the first place when the look is
> > broken out immediately?
> 
> About checking the flags:
> 
> https://lore.kernel.org/linux-mm/20190320081643.3c4m5tec5vx653sn@d104.suse.de/#t

This didn't really help. Maybe the code was different back then but
right now the code doesn't make much sense TBH. The only reason to check
inside the loop would be to have a completely unpopulated address range.
Note about MPOL_MF_STRICT is not checked explicitly and I do not see how
it makes any difference.

Anyway this function would benefit from some uncluttering!

-- 
Michal Hocko
SUSE Labs