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Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20]  5: Uprobes:
 register/unregister probes.
From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
        Linux-mm <linux-mm@kvack.org>,
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        Oleg Nesterov <oleg@redhat.com>,
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Date: Thu, 27 Jan 2011 11:29:36 +0100
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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..