linux-kernel - Re: [PATCH 1/2] ftrace: nmi safe code modification

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Message-ID: <20081030203810.GM27407@elte.hu>
Date:	Thu, 30 Oct 2008 21:38:10 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, peterz@...radead.org,
	torvalds@...ux-foundation.org, srostedt@...hat.com
Subject: Re: [PATCH 1/2] ftrace: nmi safe code modification


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> > +	/* make sure NMIs see the cleared bit */
> > +	smp_mb();
> > +
> > +	wait_for_nmi();
> > +
> > +	return mod_code_status;
> > +}
> 
> I guess the weakness here is that the code will only allow a single 
> contiguous hunk of text to be modified.  One could envisage 
> situations where two or more separate areas of memory need to be 
> modified atomically/together.
> 
> I guess we can cross that bridge when we fall off it.

yeah - the whole 'transaction' concept can be extended easily, in just 
one place.

Not that i think that it would really be useful to go beyond the 
current (target,len) abstraction - the less complex code patching is 
done, the better.

	Ingo
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