linux-kernel - Re: [PATCH] mmap.2: MAP_FIXED is okay if the address range has been reserved

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Message-ID: <20180413064917.GC17484@dhcp22.suse.cz>
Date:   Fri, 13 Apr 2018 08:49:17 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     John Hubbard <jhubbard@...dia.com>, Jann Horn <jannh@...gle.com>,
        linux-man <linux-man@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mmap.2: MAP_FIXED is okay if the address range has been
 reserved

On Fri 13-04-18 08:43:27, Michael Kerrisk wrote:
[...]
> So, you mean remove this entire paragraph:
> 
>               For cases in which the specified memory region has not been
>               reserved using an existing mapping,  newer  kernels  (Linux
>               4.17  and later) provide an option MAP_FIXED_NOREPLACE that
>               should be used instead; older kernels require the caller to
>               use addr as a hint (without MAP_FIXED) and take appropriate
>               action if the kernel places the new mapping at a  different
>               address.
> 
> It seems like some version of the first half of the paragraph is worth 
> keeping, though, so as to point the reader in the direction of a remedy.
> How about replacing that text with the following:
> 
>               Since  Linux 4.17, the MAP_FIXED_NOREPLACE flag can be used
>               in a multithreaded program to avoid  the  hazard  described
>               above.

Yes, that sounds reasonable to me.

-- 
Michal Hocko
SUSE Labs