linux-kernel - Re: probe_event_disable()->synchronize

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Message-ID: <87d2dl4kno.fsf@sejong.aot.lge.com>
Date:	Fri, 04 Jul 2014 17:01:47 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.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,
	"yrl.pp-manager.tt\@hitachi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: probe_event_disable()->synchronize_sched()

Hi Masami,

On Fri, 04 Jul 2014 10:00:51 +0900, Masami Hiramatsu wrote:
> (2014/07/03 16:44), Namhyung Kim wrote:
>> Hi Masami,
>> 
>> On Thu, 03 Jul 2014 14:46:09 +0900, Masami Hiramatsu wrote:
>>> One possible scenario is here; someone disables an event and tries to remove
>>> it (both will be done by different syscalls). If we don't synchronize
>>> the first disabling, the event flag set disabled, but the event itself
>>> is not disabled. Thus event handler is still possible to be running
>>> somewhere when it is removed.
>> 
>> But, IIUC both of disable and remove path are protected by event_mutex.
>> So one cannot see the case of disabled event flag but enabled event, no?
>
> No, the flag is not protect the trace event handler itself.
> I meant that running handlers and the flag was not synchronized.

Ah, right.  Thanks for explanation. :)

Thanks,
Namhyung
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