Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752862AbbLRGZG (ORCPT ); Fri, 18 Dec 2015 01:25:06 -0500 Received: from helcar.hengli.com.au ([209.40.204.226]:48020 "EHLO helcar.hengli.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751899AbbLRGZD (ORCPT ); Fri, 18 Dec 2015 01:25:03 -0500 Date: Fri, 18 Dec 2015 14:24:50 +0800 From: Herbert Xu To: kernel test robot Cc: lkp@01.org, LKML , Colin Ian King , 0day robot , netdev@vger.kernel.org Subject: rhashtable: Kill harmless RCU warning in rhashtable_walk_init Message-ID: <20151218062450.GA19749@gondor.apana.org.au> References: <874mfgedrp.fsf@yhuang-dev.intel.com> <20151218053416.GA19479@gondor.apana.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151218053416.GA19479@gondor.apana.org.au> 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: 2750 Lines: 64 On Fri, Dec 18, 2015 at 01:34:16PM +0800, Herbert Xu wrote: > On Fri, Dec 18, 2015 at 09:39:22AM +0800, kernel test robot wrote: > > FYI, we noticed the below changes on > > > > https://github.com/0day-ci/linux Herbert-Xu/rhashtable-Fix-walker-list-corruption/20151216-164833 > > commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable: Fix walker list corruption") > > > > [ 8.933376] =============================== > > [ 8.933376] =============================== > > [ 8.934629] [ INFO: suspicious RCU usage. ] > > [ 8.934629] [ INFO: suspicious RCU usage. ] > > [ 8.935941] 4.4.0-rc3-00995-gf9f51b8 #2 Not tainted > > [ 8.935941] 4.4.0-rc3-00995-gf9f51b8 #2 Not tainted > > [ 8.937494] ------------------------------- > > [ 8.937494] ------------------------------- > > [ 8.938818] lib/rhashtable.c:504 suspicious rcu_dereference_protected() usage! > > [ 8.938818] lib/rhashtable.c:504 suspicious rcu_dereference_protected() usage! > > This is actually a false positive because the new spin lock that > we hold prevents ht->tbl from disappearing under us. So here is > a patch to kill the warning with a comment. Resent with a proper patch subject and reported-by. ---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_raw and adding a comment. Reported-by: kernel test robot Signed-off-by: Herbert Xu diff --git a/lib/rhashtable.c b/lib/rhashtable.c index eb9240c..3404b06 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -519,7 +519,11 @@ int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter) return -ENOMEM; spin_lock(&ht->lock); - iter->walker->tbl = rht_dereference(ht->tbl, ht); + /* We do not need RCU protection because we hold ht->lock + * which guarantees that if we see ht->tbl then it won't + * die on us. + */ + iter->walker->tbl = rcu_dereference_raw(ht->tbl); list_add(&iter->walker->list, &iter->walker->tbl->walkers); spin_unlock(&ht->lock); -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- 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/