linux-kernel - Re: [PATCH 5/7] uretprobes: return probe exit, invoke handlers

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Message-ID: <20130325163800.GA8324@redhat.com>
Date:	Mon, 25 Mar 2013 17:38:00 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: Re: [PATCH 5/7] uretprobes: return probe exit, invoke handlers

On 03/25, Anton Arapov wrote:
>
> On Sun, Mar 24, 2013 at 05:28:17PM +0100, Oleg Nesterov wrote:
> >
> > Ignoring the fact you need put_uprobe/kfree, it seems that we should
> > do something like this,
> >
> > 	do {
> > 		handler_uretprobe_chain(...);
> >
> > 		if (!ri->dirty)	// not chained
> > 			break;
> >
> > 		ri = ri->next;
> > 	} while (ri);
> >
> > 	utask->return_instances = ri;
> > No?
>
> Oleg, Do you mean
>
>  	do {
>  		handler_uretprobe_chain(...);
>
>         ri = ri->next;
>
>  		if (!ri->dirty)	// not chained
>  			break;
>   	} while (ri);
>
>  	utask->return_instances = ri;
>
> otherwise we stuck with the first instance in stack.

Not sure I understand... but it is very possible I missed something.

But the pseudo code I wrote is not correct, I meant

	utask->return_instances = ri->next;

after the main loop.

> ...and perhaps for(;;) would be 'more beautiful' here?

Oh, I would not mind either way. In fact we do not really need
ri != NULL check inside the loop (again, unless I am confused).
We must see a non-chained entry in the stack unless we have a
bug.

Oleg.

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