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Subject: Re: [PATCH v4 3.0-rc2-tip 7/22]  7: uprobes: mmap and fork hooks.
From: Peter Zijlstra <peterz@infradead.org>
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Date: Tue, 21 Jun 2011 15:17:23 +0200
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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>, Andi Kleen <andi@firstfloor.org>, Hugh Dickins <hughd@google.com>, Christoph Hellwig <hch@infradead.org>, Jonathan Corbet <corbet@lwn.net>, Thomas Gleixner <tglx@linutronix.de>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Jim Keniston <jkenisto@linux.vnet.ibm.com>, Roland McGrath <roland@hack.frob.com>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Andrew Morton <akpm@linux-foundation.org>

On Fri, 2011-06-17 at 11:41 +0200, Peter Zijlstra wrote:
>=20
> On thing I was thinking of to fix that initial problem of spurious traps
> was to leave the uprobe in the tree but skip all probes without
> consumers in mmap_uprobe().

Can you find fault with using __unregister_uprobe() as a cleanup path
for __register_uprobe() so that we do a second vma-rmap walk, and
ignoring empty probes on uprobe_mmap()?

We won't get spurious traps because the empty (no consumers) uprobe is
still in the tree, we won't get any 'lost' probe insn because the
cleanup does a second vma-rmap walk which will include the new mmap().
And double probe insertion is harmless.


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