Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751297Ab3HSLDD (ORCPT ); Mon, 19 Aug 2013 07:03:03 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:30413 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751221Ab3HSLDB (ORCPT ); Mon, 19 Aug 2013 07:03:01 -0400 Message-ID: <5211FAB3.7080400@huawei.com> Date: Mon, 19 Aug 2013 19:00:03 +0800 From: Ding Tianhong User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130620 Thunderbird/17.0.7 MIME-Version: 1.0 To: Johannes Berg CC: Hugh Dickins , Linus Torvalds , Greg KH , "David S. Miller" , "Otcheretianski, Andrei" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "stable@vger.kernel.org" , Pravin B Shelar , Thomas Graf Subject: Re: 3.11-rc6 genetlink locking fix offends lockdep References: <1376899214.14734.6.camel@jlt4.sipsolutions.net> In-Reply-To: <1376899214.14734.6.camel@jlt4.sipsolutions.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.72.199] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1860 Lines: 60 On 2013/8/19 16:00, Johannes Berg wrote: > >> 3.11-rc6's commit 58ad436fcf49 ("genetlink: fix family dump race") >> gives me the lockdep trace below at startup. > > Hmm. Yes, I see now how this happens, not sure why I didn't run into it. > > The problem is that genl_family_rcv_msg() is called with the genl_lock > held, and then calls netlink_dump_start() with it held, creating a > genl_lock->cb_mutex dependency, but obviously the dump continuation is > the other way around. > > We could use the semaphore instead, I believe, but I don't really > understand the mutex vs. semaphore well enough to be sure that's > correct. > > johannes > it is useless, the logic need to modify or otherwise it will still call lockdep trace. maybe i could send a patch for it, if you wish. > > diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c > index f85f8a2..6cfa646 100644 > --- a/net/netlink/genetlink.c > +++ b/net/netlink/genetlink.c > @@ -792,7 +792,7 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb) > bool need_locking = chains_to_skip || fams_to_skip; > > if (need_locking) > - genl_lock(); > + down_read(&cb_lock); > > for (i = chains_to_skip; i < GENL_FAM_TAB_SIZE; i++) { > n = 0; > @@ -815,7 +815,7 @@ errout: > cb->args[1] = n; > > if (need_locking) > - genl_unlock(); > + up_read(&cb_lock); > > return skb->len; > } > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > . > -- 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/