linux-kernel - Re: [PATCH RFC v2 1/4] cgroup: implement eventfd-based generic API for notifications

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Date:	Tue, 15 Dec 2009 17:03:37 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Dan Malek <dan@...eddedalley.com>,
	Vladislav Buzov <vbuzov@...eddedalley.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH RFC v2 1/4] cgroup: implement eventfd-based generic API 
	for notifications

On Tue, Dec 15, 2009 at 11:35 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Tue, 15 Dec 2009 11:11:16 +0200
> "Kirill A. Shutemov" <kirill@...temov.name> wrote:
>
>> Could anybody review the patch?
>>
>> Thank you.
>
> some nitpicks.
>
>>
>> On Sat, Dec 12, 2009 at 12:59 AM, Kirill A. Shutemov
>> <kirill@...temov.name> wrote:
>
>> > +       /*
>> > +        * Unregister events and notify userspace.
>> > +        * FIXME: How to avoid race with cgroup_event_remove_work()
>> > +        *        which runs from workqueue?
>> > +        */
>> > +       mutex_lock(&cgrp->event_list_mutex);
>> > +       list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
>> > +               cgroup_event_remove(event);
>> > +               eventfd_signal(event->eventfd, 1);
>> > +       }
>> > +       mutex_unlock(&cgrp->event_list_mutex);
>> > +
>> > +out:
>> >        return ret;
>> >  }
>
> How ciritical is this FIXME ?
> But Hmm..can't we use RCU ?

It's not reasonable to have RCU here, since event_list isn't mostly-read.
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