linux-kernel - Re: [patch 1/3] Text Edit Lock

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Message-Id: <200706190105.10803.ak@suse.de>
Date:	Tue, 19 Jun 2007 01:05:10 +0200
From:	Andi Kleen <ak@...e.de>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	prasanna@...ibm.com, ananth@...ibm.com, jkenisto@...ibm.com
Subject: Re: [patch 1/3] Text Edit Lock - i386

On Tuesday 19 June 2007 00:52:25 Chuck Ebbert wrote:
> On 06/18/2007 05:58 PM, Mathieu Desnoyers wrote:
> > Interface to use for code patching : uses a mutex to insure mutual edit
> > exclusion and makes sure the page is writable.
> > 
> ... 
> > +/* Mutex protecting text section modification (dynamic code patching) */
> > +static DEFINE_MUTEX(text_mutex);
> > +
> 
> Probably should be a spinlock.
> 
> And it just occurred to me, how does smp_alternatives deal with this?
> Is it broken now when the text section is read-only?

The text section is only changed to ro very late,  alternative code
runs earlier.

But when you unplug all CPUs to go back to UP I suspect it may break.

-Andi
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