Subject: Re: [PATCH v4 3.0-rc2-tip 7/22]  7: uprobes: mmap and fork hooks.
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>,
        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>
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Date: Tue, 21 Jun 2011 15:17:23 +0200
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On Fri, 2011-06-17 at 11:41 +0200, Peter Zijlstra wrote:
> 
> 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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