Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760042Ab3CHBaa (ORCPT ); Thu, 7 Mar 2013 20:30:30 -0500 Received: from dcvr.yhbt.net ([64.71.152.64]:51068 "EHLO dcvr.yhbt.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752366Ab3CHBa2 (ORCPT ); Thu, 7 Mar 2013 20:30:28 -0500 Date: Fri, 8 Mar 2013 01:30:27 +0000 From: Eric Wong To: Arve =?utf-8?B?SGrDuG5uZXbDpWc=?= Cc: NeilBrown , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Davide Libenzi , Alexander Viro , linux-fsdevel@vger.kernel.org, Andrew Morton Subject: Re: epoll: possible bug from wakeup_source activation Message-ID: <20130308013027.GA31830@dcvr.yhbt.net> References: <20130307112639.GA25130@dcvr.yhbt.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130307112639.GA25130@dcvr.yhbt.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2086 Lines: 61 Eric Wong wrote: > Hi Arve, looking at commit 4d7e30d98939a0340022ccd49325a3d70f7e0238 > (epoll: Add a flag, EPOLLWAKEUP, to prevent suspend ...) > > I think the reason for using ep->ws instead of epi->ws in the unlikely > ovflist case applies to the likely rdllist case, too. Since epi->ws is > only protected by ep->mtx, it can also be deactivated while inside > ep_poll_callback. > > So something like the following patch might be necessary > (shown here with extra context): > > --- a/fs/eventpoll.c > +++ b/fs/eventpoll.c > @@ -968,39 +968,45 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k > if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) { > if (epi->next == EP_UNACTIVE_PTR) { > epi->next = ep->ovflist; > ep->ovflist = epi; > if (epi->ws) { > /* > * Activate ep->ws since epi->ws may get > * deactivated at any time. > */ > __pm_stay_awake(ep->ws); > } > > } Thinking about this more, it looks like the original ep->ovflist case of using ep->ws is unnecessary. ep->ovflist != EP_UNACTIVE_PTR can only happen while ep->mtx is held (in ep_scan_ready_list); which means ep_modify+friends cannot remove epi->ws. ep_poll_callback holding ep->lock means ep_poll_callback prevents ep_scan_ready_list from setting ep->ovflist = EP_UNACTIVE_PTR and releasing ep->mtx. > goto out_unlock; > } > > /* If this file is already in the ready list we exit soon */ > if (!ep_is_linked(&epi->rdllink)) { > list_add_tail(&epi->rdllink, &ep->rdllist); > - __pm_stay_awake(epi->ws); > + if (epi->ws) { > + /* > + * Activate ep->ws since epi->ws may get > + * deactivated at any time. > + */ > + __pm_stay_awake(ep->ws); > + } > } I still think ep->ws needs to be used in the common ep->rdllist case. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/