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Date: Wed, 26 Jan 2011 21:00:36 +0530
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
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>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        SystemTap <systemtap@sources.redhat.com>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Andi Kleen <andi@firstfloor.org>, LKML <linux-kernel@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20]  5: Uprobes:
 register/unregister probes.
Message-ID: <20110126153036.GN19725@linux.vnet.ibm.com>
Reply-To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
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* Peter Zijlstra <peterz@infradead.org> [2011-01-26 11:11:48]:

> 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.

When we do the actual insert/remove of the breakpoint we hold the
mmap_sem. During the actual insertion/removal, if the vma for the
specific inode is not found, we just come out without doing the
actual insertion/deletion.

-- 
Thanks and Regards
Srikar