linux-kernel - Re: Use of copy_from_user in msm_gem_submit.c while holding a spin

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Date:	Wed, 17 Aug 2016 20:31:20 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Rob Clark <robdclark@...il.com>
Cc:	Vaishali Thakkar <vaishali.thakkar@...cle.com>,
	David Airlie <airlied@...ux.ie>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	freedreno@...ts.freedesktop.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: Use of copy_from_user in msm_gem_submit.c while holding a
 spin_lock

On Wed, Aug 17, 2016 at 03:24:38PM -0400, Rob Clark wrote:

> hmm, looks like, at least on arm (not sure about arm64),
> 
> #define __copy_from_user_inatomic __copy_from_user
> 
> ie. copy_from_user() minus the access_ok() and memset in the
> !access_ok() path.. but maybe what I want is just the
> pagefault_disable() if that disables copy_from_user() being able to
> block..

On a bunch of platforms copy_from_user() starts with might_sleep(); again,
that'll spread to all of the pretty soon.

Right now those primitives are very badly out of sync; this will change,
but let's not add more PITA sources.