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Subject: Re: [PATCHv11 2.6.36-rc2-tip 5/15]  5: uprobes: Uprobes
 (un)registration and exception handling.
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>,
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Date: Mon, 06 Sep 2010 20:15:21 +0200
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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.