linux-kernel - Re: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes

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Message-ID: <20100114113509.GB5033@nowhere>
Date:	Thu, 14 Jan 2010 12:35:12 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	utrace-devel <utrace-devel@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes

On Thu, Jan 14, 2010 at 12:23:11PM +0100, Peter Zijlstra wrote:
> On Mon, 2010-01-11 at 17:56 +0530, Srikar Dronamraju wrote:
> > This patch implements ftrace plugin for uprobes.
> 
> Right, like others have said, trace events is a much saner interface.
> 
> So the easiest way I can see that working is to register uprobes against
> a file (not a pid). Then on creation it uses rmap to find all current
> maps of that file and install the probe if there is a consumer for that
> map.
> 
> Then for each new mmap() of that file, we also need to check if there's
> a consumer ready and install the probe.



That looks racy.

Say you first create a probe on /bin/ls:

perf probe p addr_in_ls /bin/ls

then something else launches /bin/ls behind you, probe
is set on it

then you launch:

perf record -e "probe:...." /bin/ls

Then it goes recording the previous instance.

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