linux-kernel - Re: [patch 3.5-rc3] mm, mempolicy: fix mbind() to do synchronous migration

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Date:	Thu, 21 Jun 2012 18:45:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 3.5-rc3] mm, mempolicy: fix mbind() to do synchronous
 migration

On Thu, 21 Jun 2012 17:46:52 -0700 Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Jun 21, 2012 at 4:46 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >
> > I can't really do anything with this patch - it's a bug added by
> > Peter's "mm/mpol: Simplify do_mbind()" and added to linux-next via one
> > of Ingo's trees.
> >
> > And I can't cleanly take the patch over as it's all bound up with the
> > other changes for sched/numa balancing.
> 
> I took the patch, it looked obviously correct (passing in a boolean
> was clearly crap).

Ah, OK, the bug was actually "retained" by "mm/mpol: Simplify do_mbind()".

I do still ask what the plans are for that patchset..

> I wonder if I should make sparse warn about any casts to/from enums.
> They tend to always be wrong.

I think it would be worth trying, see how much fallout there is.  Also
casts from "enum a" to "enum b".  We've had a few of those,
unintentionally.

And casts to/from bool, perhaps.  To squish the warning we'd do things
like a_bool = !!a_int.  That generates extra code, but gcc internally
generates extra code for a_bool = a_int anyway, and a quick test here
indicates that the generated code is identical (testl/setne).

It would be nice to find a way of converting an integer which is known
to be 1 or 0 into a bool without generating any code, but I haven't
found a way of tricking the compiler into doing that.  It's all a bit
of a downside to using bool at all.
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