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

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Message-Id: <20091216085552.91ebc559.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 16 Dec 2009 08:55:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
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, 15 Dec 2009 17:03:37 +0200
"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.
> 
ok.

Thanks,
-Kame

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