linux-kernel - Re: [PATCHv11 2.6.36-rc2-tip 5/15] 5: uprobes: Uprobes (un)registration and exception handling.

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Date:	Mon, 06 Sep 2010 20:15:21 +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>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCHv11 2.6.36-rc2-tip 5/15]  5: uprobes: Uprobes
 (un)registration and exception handling.

On Mon, 2010-09-06 at 23:16 +0530, Srikar Dronamraju wrote:
> > > Unlike kernel probing, uprobes has a disadvantage.
> > > Lets assume that the request for removing a probepoint when some of the
> > > threads have actually hit the probe. Because the handlers in uprobes can
> > > sleep, we cant remove the probepoint at the same time as the request for
> > > the removing the probe. This is where refcount steps in and helps us to
> > > decide when we can remove the probepoint. Even inoode based
> > > tracing or file based tracing would need it.
> > 
> > Stick the refcount in the actual struct uprobe instead?
> 
> What if the called does something like this when one or more
> threads are processing the breakpoint.
> unregister_uprobe(u);
> kfree(u);

That's what atomic_inc_unless_zero() and RCU are for.
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