linux-kernel - Re: [PATCH 1/1] x86: fix text

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Message-ID: <48126A80.4000203@redhat.com>
Date:	Fri, 25 Apr 2008 19:34:24 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Ingo Molnar <mingo@...e.hu>, Jiri Slaby <jirislaby@...il.com>,
	David Miller <davem@...emloft.net>, zdenek.kabelac@...il.com,
	rjw@...k.pl, paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	linux-ext4@...r.kernel.org, herbert@...dor.apana.org.au,
	penberg@...helsinki.fi, clameter@....com,
	linux-kernel@...r.kernel.org, pageexec@...email.hu,
	"Frank Ch. Eigler" <fche@...hat.com>, systemtap@...rces.redhat.com
Subject: Re: [PATCH 1/1] x86: fix text_poke

Jeremy Fitzhardinge wrote:
> Mathieu Desnoyers wrote:
>> This idea has been considered a few years ago at OLS in the tracing BOF
>> if I remember well.  The results were this : First, there is no way to
>> guarantee that no code path, nor any return address from any function,
>> interrupt, sleeping thread, will return to the "old" version of the
>> function. Nor is it possible to determine when a quiescent state is
>> reached. Therefore, we couldn't see how we can do the teardown.
>>   
> 
> Does that matter?  The new function is semantically identical to the old 
> one, and the old code will remain in place.  If there's still users in 
> the old function it may take a while for them to get flushed out (and 
> won't be traced in the meantime), but you have to expect some missed 
> events if you're shoving any kind of dynamic marker into the code.  The 
> main problem is if there's something still depending on the first 5 
> bytes of the function (most likely if there's a loop head somewhere near 
> the top of the function).

I think we have to ensure no threads sleeping or being interrupted on
the function when removing new function. How would you check it?

-- 
Masami Hiramatsu

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

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

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