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Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
- From: Peter Zijlstra <peterz at infradead dot org>
- To: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, Linux-mm <linux-mm at kvack dot org>, Arnaldo Carvalho de Melo <acme at infradead dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Christoph Hellwig <hch at infradead dot org>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Oleg Nesterov <oleg at redhat dot com>, Andrew Morton <akpm at linux-foundation dot org>, SystemTap <systemtap at sources dot redhat dot com>, Jim Keniston <jkenisto at linux dot vnet dot ibm dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Andi Kleen <andi at firstfloor dot org>, LKML <linux-kernel at vger dot kernel dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>
- Date: Wed, 26 Jan 2011 11:11:48 +0100
- Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
- References: <20101216095714.23751.52601.sendpatchset@localhost6.localdomain6> <20101216095817.23751.76989.sendpatchset@localhost6.localdomain6> <1295957744.28776.722.camel@laptop> <20110126075558.GB19725@linux.vnet.ibm.com>
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.