Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750850Ab3HSIA1 (ORCPT ); Mon, 19 Aug 2013 04:00:27 -0400 Received: from s3.sipsolutions.net ([144.76.43.152]:50182 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750734Ab3HSIAZ (ORCPT ); Mon, 19 Aug 2013 04:00:25 -0400 Message-ID: <1376899214.14734.6.camel@jlt4.sipsolutions.net> Subject: Re: 3.11-rc6 genetlink locking fix offends lockdep From: Johannes Berg To: Hugh Dickins Cc: 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 Date: Mon, 19 Aug 2013 10:00:14 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1391 Lines: 47 > 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 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 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/