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

From: Michal Hocko <mhocko@kernel.org>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>, Jann Horn <jannh@google.com>,
	linux-man <linux-man@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] mmap.2: MAP_FIXED is okay if the address range has been reserved
Date: Fri, 13 Apr 2018 08:49:17 +0200	[thread overview]
Message-ID: <20180413064917.GC17484@dhcp22.suse.cz> (raw)
In-Reply-To: <9c714917-fc29-4d12-b5e8-cff28761a2c1@gmail.com>

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