linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.

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Date:	Thu, 27 Jan 2011 11:29:36 +0100
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>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20]  5: Uprobes:
 register/unregister probes.

On Thu, 2011-01-27 at 15:31 +0530, Srikar Dronamraju wrote:
> 
> > You can, if only to wreck your thing, you can call mmap() as often as
> > you like (until your virtual memory space runs out) and get many many
> > mapping of the same file.
> > 
> > It doesn't need to make sense to the linker, all it needs to do is
> > confuse your code ;-)
> 
> Currently if there are multiple mappings of the same executable
> code, only one mapped area would have the breakpoint inserted.

Right, so you could use it to make debugging harder..

> If the code were to execute from some other mapping, then it would
> work as if there are no probes.  However if the code from the
> mapping that had the breakpoint executes then we would see the
> probes.
> 
> If we want to insert breakpoints in each of the maps then we
> would have to extend mm->uprobes_vaddr.
> 
> Do you have any other ideas to tackle this?

Supposing I can get my preemptible mmu patches anywhere.. you could
simply call install_uprobe() while holding the i_mmap_mutex ;-)

> Infact do you think we should be handling this case?

I'm really not sure how often this would happen, but dealing with it
sure makes me feel better..
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