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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>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Christoph Hellwig <hch@infradead.org>,
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        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
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Date: Wed, 26 Jan 2011 11:11:48 +0100
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On Wed, 2011-01-26 at 13:25 +0530, Srikar Dronamraju wrote:
> 
> > > +
> > > +               list_add(&mm->uprobes_list, &tmp_list);
> > > +               mm->uprobes_vaddr = vma->vm_start + offset;
> > > +       }
> > > +       spin_unlock(&mapping->i_mmap_lock);
> > 
> > Both this and unregister are racy, what is to say:
> >  - the vma didn't get removed from the mm
> >  - no new matching vma got added
> > 
> 
> register_uprobe, unregister_uprobe, uprobe_mmap are all synchronized by
> uprobes_mutex. So I dont see one unregister_uprobe getting thro when
> another register_uprobe is working with a vma.
> 
> If I am missing something elementary, please explain a bit more.

afaict you're not holding the mmap_sem, so userspace can simply unmap
the vma.