From: Matthew Wilcox <willy@infradead.org>
To: john.hubbard@gmail.com
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
linux-man <linux-man@vger.kernel.org>,
linux-api@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH] mmap.2: MAP_FIXED is no longer discouraged
Date: Sat, 2 Dec 2017 07:05:55 -0800 [thread overview]
Message-ID: <20171202150554.GA30203@bombadil.infradead.org> (raw)
In-Reply-To: <20171202021626.26478-1-jhubbard@nvidia.com>
On Fri, Dec 01, 2017 at 06:16:26PM -0800, john.hubbard@gmail.com wrote:
> MAP_FIXED has been widely used for a very long time, yet the man
> page still claims that "the use of this option is discouraged".
I think we should continue to discourage the use of this option, but
I'm going to include some of your text in my replacement paragraph ...
-Because requiring a fixed address for a mapping is less portable,
-the use of this option is discouraged.
+The use of this option is discouraged because it forcibly unmaps any
+existing mapping at that address. Programs which use this option need
+to be aware that their memory map may change significantly from one run to
+the next, depending on library versions, kernel versions and random numbers.
+In a threaded process, checking the existing mappings can race against
+a new dynamic library being loaded, for example in response to another
+thread making a library call which causes a PAM module to be loaded.
(I don't love this text, in particular "PAM module". I'm going off to
use the ATM machine now. Please edit.)
next prev parent reply other threads:[~2017-12-02 15:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-02 2:16 [PATCH] mmap.2: MAP_FIXED is no longer discouraged john.hubbard-Re5JQEeQqe8AvxtiuMwx3w
2017-12-02 15:05 ` Matthew Wilcox [this message]
2017-12-02 18:49 ` Jann Horn
[not found] ` <CAG48ez2u3fjBDCMH4x3EUhG6ZD6VUa=A1p441P9fg=wUdzwHNQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-02 22:19 ` Matthew Wilcox
[not found] ` <20171202221910.GA8228-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-12-03 0:22 ` John Hubbard
2017-12-03 4:06 ` John Hubbard
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