linux-kernel - Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump optimization

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Message-ID: <20091124033135.GE6752@nowhere>
Date:	Tue, 24 Nov 2009 04:31:37 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump
	optimization

On Tue, Nov 24, 2009 at 03:44:19AM +0100, Frederic Weisbecker wrote:
> On Mon, Nov 23, 2009 at 06:21:41PM -0500, Masami Hiramatsu wrote:
> > +static void kprobe_optimizer(struct work_struct *work);
> > +static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
> > +#define OPTIMIZE_DELAY 5
> > +
> > +/* Kprobe jump optimizer */
> > +static __kprobes void kprobe_optimizer(struct work_struct *work)
> > +{
> > +	struct optimized_kprobe *op, *tmp;
> > +
> > +	/* Lock modules while optimizing kprobes */
> > +	mutex_lock(&module_mutex);
> > +	mutex_lock(&kprobe_mutex);
> > +	if (kprobes_all_disarmed)
> > +		goto end;
> > +
> > +	/* Wait quiesence period for ensuring all interrupts are done */
> > +	synchronize_sched();
> 
> 
> 
> It's not clear to me why you are doing that.
> Is this waiting for pending int 3 kprobes handlers
> to complete? If so, why, and what does that prevent?


I _might_ have understood.
You have set up the optimized flags, then you wait for
any old-style int 3 kprobes to complete and route
to detour buffer so that you can patch the jump
safely in the dead code? (and finish with first byte
by patching the int 3 itself)

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