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Message-ID: <1422111397.1038.53.camel@freebsd.org>
Subject: Re: svn commit: r277643 - in head/sys: arm/arm dev/mem i386/i386
 mips/mips sparc64/sparc64
From: Ian Lepore <ian@freebsd.org>
To: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 24 Jan 2015 07:56:37 -0700
In-Reply-To: <201501241251.t0OCpGa8053192@svn.freebsd.org>
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On Sat, 2015-01-24 at 12:51 +0000, Konstantin Belousov wrote:
> Author: kib
> Date: Sat Jan 24 12:51:15 2015
> New Revision: 277643
> URL: https://svnweb.freebsd.org/changeset/base/277643
> 
> Log:
>   Remove Giant from /dev/mem and /dev/kmem.  It is definitely not needed
>   for i386, and from the code inspection, nothing in the
>   arm/mips/sparc64 implementations depends on it.
>   

I'm not sure I agree with that.  On arm the memrw() implementation uses
a single statically-allocated page of kva space into which it maps each
physical page in turn in the main loop.  What prevents preemption or
multicore access to /dev/mem from trying to use that single page for
multiple operations at once?

-- Ian