linux-kernel - Re: [RFC] [PATCH 0/7] UBP, XOL and Uprobes [ Summary of Comments and actions to be taken ]

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Date:	Wed, 27 Jan 2010 07:53:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	ananth@...ibm.com
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	utrace-devel <utrace-devel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Avi Kivity <avi@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Mel Gorman <mel@....ul.ie>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 0/7] UBP, XOL and Uprobes [ Summary of Comments
 and actions to be taken ]

On Fri, 2010-01-22 at 12:54 +0530, Ananth N Mavinakayanahalli wrote:
> On Fri, Jan 22, 2010 at 12:32:32PM +0530, Srikar Dronamraju wrote:
> > Here is a summary of the Comments and actions that need to be taken for
> > the current uprobes patchset. Please let me know if I missed or
> > misunderstood any of your comments.  
> > 
> > 1. Uprobes depends on trap signal.
> > 	Uprobes depends on trap signal rather than hooking to the global
> > die notifier. It was suggested that we hook to the global die notifier.
> > 
> > 	In the next version of patches, Uprobes will use the global die
> > 	notifier and look at the per-task count of the probes in use to
> > 	see if it has to be consumed.
> > 
> > 	However this would reduce the ability of uprobe handlers to
> > 	sleep. Since we are dealing with userspace, sleeping in handlers
> > 	would have been a good feature. We are looking at ways to get
> > 	around this limitation.
> 
> We could set a TIF_ flag in the notifier to indicate a breakpoint hit
> and process it in task context before the task heads into userspace.

OK, so we can go play stack games in the INT3 interrupt handler by
moving to a non IST stack when it comes from userspace, or move kprobes
over to INT1 or something.

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