linux-kernel - Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range

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Message-ID: <alpine.DEB.2.00.1010181430220.15782@chino.kir.corp.google.com>
Date:	Mon, 18 Oct 2010 14:30:25 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range

On Mon, 18 Oct 2010, Thomas Gleixner wrote:

> I agree in general, but this is stupid as hell. No fcking interface
> should exposed kernel internal flag bits just as hex values and no
> fcking luser space should rely on it to be a subject of no change.
> 
> Seriously, if we can't even change TIF_* bits anymore then we are
> doing something wrong. That's a pure kernel internal affair and
> subject to change.
> 

I agree, and when I added them to the show_state() dumps, I should have 
probably enumerated the bits of interest to userspace and printed them 
much like taint flags: use 'M' for my bit of interest, TIF_MEMDIE, which 
gives access to memory reserves.  We care a _lot_ about detecting hung 
tasks that have that bit set because it usually indicates a VM problem 
where we've allowed complete depletion of memory reserves.  There's no 
other way to detect that, so we need to export TIF_MEMDIE somehow and if 
that's by doing (ti->flags & TIF_MEMDIE) ? "M" : "" then that's fine by 
me.  I hope we can do that before changing its value, though.
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