linux-kernel - Re: [PATCH 16/17] uprobes: Allocate ->utask before handler

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Date:	Tue, 10 Dec 2013 19:41:27 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH 16/17] uprobes: Allocate ->utask before handler_chain()
 for tracing handlers

(2013/12/09 15:20), Namhyung Kim wrote:
> From: Oleg Nesterov <oleg@...hat.com>
> 
> uprobe_trace_print() and uprobe_perf_print() need to pass the additional
> info to call_fetch() methods, currently there is no simple way to do this.
> 
> current->utask looks like a natural place to hold this info, but we need
> to allocate it before handler_chain().
> 
> This is a bit unfortunate, perhaps we will find a better solution later,
> but this is simnple and should work right now.

Hmm, when this will happen? and isn't it better to increment
miss-hit counter of the uprobe?

Thank you,

> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  kernel/events/uprobes.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 24b7d6ca871b..3cc8e0bb8acf 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1828,6 +1828,10 @@ static void handle_swbp(struct pt_regs *regs)
>  	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
>  		goto out;
>  
> +	/* Tracing handlers use ->utask to communicate with fetch methods */
> +	if (!get_utask())
> +		goto out;
> +
>  	handler_chain(uprobe, regs);
>  	if (can_skip_sstep(uprobe, regs))
>  		goto out;
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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