From: Namhyung Kim <namhyung@kernel.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        "zhangwei\(Jovi\)" <jovi.zhangwei@huawei.com>,
        linux-kernel@vger.kernel.org,
        "yrl.pp-manager.tt\@hitachi.com" <yrl.pp-manager.tt@hitachi.com>
Subject: Re: probe_event_disable()->synchronize_sched()
References: <20140627170116.GA18298@redhat.com>
	<20140627170136.GA18319@redhat.com>
	<87k37z54lu.fsf@sejong.aot.lge.com>
	<20140630184828.GA24594@redhat.com>
	<20140701193147.GA32492@redhat.com> <53B4EE21.2040203@hitachi.com>
	<87lhsa51kg.fsf@sejong.aot.lge.com> <53B5FCC3.8010303@hitachi.com>
Date: Fri, 04 Jul 2014 17:01:47 +0900
In-Reply-To: <53B5FCC3.8010303@hitachi.com> (Masami Hiramatsu's message of
	"Fri, 04 Jul 2014 10:00:51 +0900")
Message-ID: <87d2dl4kno.fsf@sejong.aot.lge.com>
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Sender: linux-kernel-owner@vger.kernel.org

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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