linux-kernel - Re: [PATCH v2 02/13] uprobes: allow ignoring of probe hits

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Message-ID: <20131028185425.GA12863@redhat.com>
Date:	Mon, 28 Oct 2013 19:54:25 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Long <dave.long@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, Rabin Vincent <rabin@....in>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/13] uprobes: allow ignoring of probe hits

David, sorry for delay.

On 10/19, Oleg Nesterov wrote:
>
> On 10/15, David Long wrote:
> >
> > @@ -1732,9 +1732,6 @@ static void handle_swbp(struct pt_regs *regs)
> >  		return;
> >  	}
> >
> > -	/* change it in advance for ->handler() and restart */
> > -	instruction_pointer_set(regs, bp_vaddr);
> > -
>
> Well, this looks obviously wrong. This SET_IP() has the comment ;)
>
> Note also that with this breaks __skip_sstep() on x86.

Hmm. Thinking more, it seems that this patch has another problem.

IIUC, the whole point of arch_uprobe_ignore() is to avoid
handler_chain() if the condition was not satisfied, so you need
to call it before handler_chain() ?

Otherwise this logic should go into can_skip_sstep() and we simply
do not need the new hook, just we need to tweak the (ugly)
UPROBE_SKIP_SSTEP logic.

Oleg.

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