linux-kernel - Re: [PATCH v4 3.0-rc2-tip 7/22] 7: uprobes: mmap and fork hooks.

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Date:	Tue, 21 Jun 2011 15:17:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 3.0-rc2-tip 7/22]  7: uprobes: mmap and fork hooks.

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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