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

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Message-ID: <20201016131531.GK22589@dhcp22.suse.cz>
Date:   Fri, 16 Oct 2020 15:15:31 +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 15:11:17, Michal Hocko wrote:
> 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.

Ohh, I have missed queue_pages_required. Let me think some more.

-- 
Michal Hocko
SUSE Labs