linux-kernel - Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

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Date:	Thu, 22 Aug 2013 12:42:12 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a
 ring buffer

On Fri, 09 Aug 2013 18:56:54 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> (2013/08/09 17:45), Namhyung Kim wrote:
> > From: Namhyung Kim <namhyung.kim@....com>
> > 
> > Fetching from user space should be done in a non-atomic context.  So
> > use a temporary buffer and copy its content to the ring buffer
> > atomically.
> > 
> > While at it, use __get_data_size() and store_trace_args() to reduce
> > code duplication.
> 
> I just concern using kmalloc() in the event handler. For fetching user
> memory which can be swapped out, that is true. But most of the cases,
> we can presume that it exists on the physical memory.
> 


What about creating a per cpu buffer when uprobes are registered, and
delete them when they are finished? Basically what trace_printk() does
if it detects that there are users of trace_printk() in the kernel.
Note, it does not deallocate them when finished, as it is never
finished until reboot ;-)

-- Steve
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