linux-kernel - Re: [PATCH 1/4] tracing/uprobes: Revert "Support mix of ftrace and perf"

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Date:	Mon, 30 Jun 2014 20:52:21 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] tracing/uprobes: Revert "Support mix of ftrace and
 perf"

(2014/06/28 2:01), Oleg Nesterov wrote:
> This reverts commit 43fe98913c9f67e3b523615ee3316f9520a623e0.
> 
> This patch is very wrong. Firstly, this change leads to unbalanced
> uprobe_unregister(). Just for example,
> 
> 	# perf probe -x /lib/libc.so.6 syscall
> 	# echo 1 >> /sys/kernel/debug/tracing/events/probe_libc/enable
> 	# perf record -e probe_libc:syscall whatever
> 
> after that uprobe is dead (unregistered) but the user of ftrace/perf
> can't know this, and it looks as if nobody hits this probe.
> 
> This would be easy to fix, but there are other reasons why it is not
> simple to mix ftrace and perf. If nothing else, they can't share the
> same ->consumer.filter. This is fixable too, but probably we need to
> fix the poorly designed uprobe_register() interface first. At least
> "register" and "apply" should be clearly separated.

Hm, it should be a uprobes original issue. it's different from kprobes.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thank you,

> 
> Cc: stable@...r.kernel.org # v3.14
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/trace_uprobe.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 04fdb5d..08e7970 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -893,6 +893,9 @@ probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
>  	int ret;
>  
>  	if (file) {
> +		if (tu->tp.flags & TP_FLAG_PROFILE)
> +			return -EINTR;
> +
>  		link = kmalloc(sizeof(*link), GFP_KERNEL);
>  		if (!link)
>  			return -ENOMEM;
> @@ -901,8 +904,12 @@ probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
>  		list_add_tail_rcu(&link->list, &tu->tp.files);
>  
>  		tu->tp.flags |= TP_FLAG_TRACE;
> -	} else
> +	} else {
> +		if (tu->tp.flags & TP_FLAG_TRACE)
> +			return -EINTR;
> +
>  		tu->tp.flags |= TP_FLAG_PROFILE;
> +	}
>  
>  	ret = uprobe_buffer_enable();
>  	if (ret < 0)
> 


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


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