linux-kernel - Re: [RFC][PATCH] x86: make text

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Message-ID: <49AC6DEA.2050304@redhat.com>
Date:	Mon, 02 Mar 2009 18:38:18 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC][PATCH] x86: make text_poke() atomic

Ingo Molnar wrote:
>>> So perhaps another approach to (re-)consider would be to go back 
>>> to atomic fixmaps here. It spends 3 slots but that's no big 
>>> deal.
>> Oh, it's a good idea! fixmaps must make it simpler.
>>
>>> In exchange it will be conceptually simpler, and will also scale 
>>> much better than a global spinlock. What do you think?
>> I think even if I use fixmaps, we have to use a spinlock to protect
>> the fixmap area from other threads...
> 
> that's why i suggested to use an atomic-kmap, not a fixmap.

Even if the mapping is atomic, text_poke() has to protect pte
from other text_poke()s while changing code.
AFAIK, atomic-kmap itself doesn't ensure that, does it?

Thank you,

> 
> 	Ingo
> --
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-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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