Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932713AbbLSEsI (ORCPT ); Fri, 18 Dec 2015 23:48:08 -0500 Received: from mga14.intel.com ([192.55.52.115]:25061 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752196AbbLSEsH (ORCPT ); Fri, 18 Dec 2015 23:48:07 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,448,1444719600"; d="scan'208";a="620550457" Date: Sat, 19 Dec 2015 12:47:59 +0800 From: Fengguang Wu To: David Miller Cc: herbert@gondor.apana.org.au, eric.dumazet@gmail.com, ying.huang@linux.intel.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, colin.king@canonical.com, lkp@01.org Subject: Re: [LKP] [PATCH v2] rhashtable: Kill harmless RCU warning in rhashtable_walk_init Message-ID: <20151219044759.GA15236@wfg-t540p.sh.intel.com> References: <20151218131408.GA21756@gondor.apana.org.au> <20151218.162731.305092674804556753.davem@davemloft.net> <20151219024528.GA27814@gondor.apana.org.au> <20151218.234259.445944618583370177.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151218.234259.445944618583370177.davem@davemloft.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2498 Lines: 68 On Fri, Dec 18, 2015 at 11:42:59PM -0500, David Miller wrote: > From: Herbert Xu > Date: Sat, 19 Dec 2015 10:45:28 +0800 > > > On Fri, Dec 18, 2015 at 04:27:31PM -0500, David Miller wrote: > >> From: Herbert Xu > >> Date: Fri, 18 Dec 2015 21:14:08 +0800 > >> > >> > On Fri, Dec 18, 2015 at 04:54:14AM -0800, Eric Dumazet wrote: > >> >> > >> >> You can avoid the comment by using the self documented and lockdep > >> >> enabled primitive > >> >> > >> >> iter->walker->tbl = rcu_dereference_protected(ht->tbl, > >> >> lockdep_is_held(&ht->lock)); > >> > > >> > That is just gross. I think a comment is much better in this case. > >> > >> Herbert, this macro was created exactly to handle this situation, > >> and this is what we do everywhere else in the tree. > > > > OK. > > > > ---8<--- > > The commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable: > > Fix walker list corruption") causes a suspicious RCU usage warning > > because we no longer hold ht->mutex when we dereference ht->tbl. > > > > However, this is a false positive because we now hold ht->lock > > which also guarantees that ht->tbl won't disppear from under us. > > > > This patch kills the warning by using rcu_dereference_protected. > > > > Reported-by: kernel test robot > > Signed-off-by: Herbert Xu > > The correct commti SHA1 is c6ff5268293ef98e48a99597e765ffc417e39fa5. > > Or at least, when I run: > > git show f9f51b8070be3e829100614a7372b219723b864f > > I get: > > fatal: bad object f9f51b8070be3e829100614a7372b219723b864f > > :-) Oops, that commit comes from 0day robot :-) > https://github.com/0day-ci/linux Herbert-Xu/rhashtable-Fix-walker-list-corruption/20151216-164833 > commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable: Fix walker list corruption") commit f9f51b8070be3e829100614a7372b219723b864f Author: Herbert Xu AuthorDate: Wed Dec 16 16:45:54 2015 +0800 Commit: 0day robot CommitDate: Wed Dec 16 16:48:36 2015 +0800 rhashtable: Fix walker list corruption Thanks, Fengguang -- 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/