linux-kernel - Re: [PATCHv11 2.6.36-rc2-tip 3/15] 3: uprobes: Slot allocation for Execution out of line(XOL)

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Date:	Mon, 06 Sep 2010 20:20:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCHv11 2.6.36-rc2-tip 3/15]  3: uprobes: Slot allocation
 for Execution out of line(XOL)

On Mon, 2010-09-06 at 23:29 +0530, Srikar Dronamraju wrote:
> 
> Lets say the thread while singlestepping the process gets
> pre-empted. Eventually the cpu might run some other thread of the same
> process before picking the first run thread. Or the first run
> thread could after migration due to load balancing or whatever end up
> running on  a different thread?  How do we handle these cases? 

So assuming we're preempted while the IP is inside the slot:

On the preempt-out we store the slot relative ip (ip - start_of_slot),
on preempt-in we write the replacement instructions in our cpu slot
(could be the same cpu, could be another) and re-position the ip to
point to the same relative position inside that slot, then go!

It really doesn't matter what happens in between.
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