lkml.org 
[lkml]   [2016]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: kmap_atomic and preemption
On Wed, May 04, 2016 at 03:47:29PM +0200, Peter Zijlstra wrote:
> Traditionally kmap_atomic() disables preemption; and the reason is that
> the returned pointer must stay valid. This had a side effect in that it
> also disabled pagefaults.

A lowmem page should never change its page_address(), so that much is
safe. I think the question is whether there is any driver code which
assumes that preemption is unconditionally disabled between a
kmap_atomic() has been called.

That wouldn't be an unreasonable assumption given the name of the
function, so I'd suggest caution with making kmap_atomic() have these
kinds of differing behaviours depending on whether we're asking to
kmap a high or lowmem page.

If we are going to allow this, I think it at least needs to be well
documented.

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

\
 
 \ /
  Last update: 2016-05-04 21:41    [W:0.103 / U:2.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site