linux-kernel - Re: [PATCH] Lock mmap_sem when calling migrate_pages() in do_move_pages_to

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Message-ID: <20180131080114.GM21609@dhcp22.suse.cz>
Date:   Wed, 31 Jan 2018 09:01:14 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] Lock mmap_sem when calling migrate_pages() in
 do_move_pages_to_node()

On Tue 30-01-18 14:12:28, Zi Yan wrote:
> On 30 Jan 2018, at 11:10, Michal Hocko wrote:
[...]
> I think the question is whether we need to hold mmap_sem for
> migrate_pages(). Hugh also agrees it is not necessary on a separate
> email. But it is held in the original code.

I would be really surprised if we really needed the lock. If we do,
however, then we really need a very good explanation why. The code used
to do so is not a valid reason.

-- 
Michal Hocko
SUSE Labs