From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753902Ab0DVXQG (ORCPT ); Thu, 22 Apr 2010 19:16:06 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:40132 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753617Ab0DVXP6 (ORCPT ); Thu, 22 Apr 2010 19:15:58 -0400 Date: Thu, 22 Apr 2010 16:15:56 -0700 From: "Paul E. McKenney" To: Vivek Goyal Cc: linux kernel mailing list , Jens Axboe , Li Zefan , Gui Jianfeng Subject: Re: [PATCH] blk-cgroup: Fix RCU correctness warning in cfq_init_queue() Message-ID: <20100422231556.GW2524@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100422155452.GD3228@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100422155452.GD3228@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 22, 2010 at 11:54:52AM -0400, Vivek Goyal wrote: > With RCU correctness on, We see following warning. This patch fixes it. This is in initialization code, so that there cannot be any concurrent updates, correct? If so, looks good. (Just wanting to make sure that we are not papering over a real error!) Thanx, Paul > [ 103.790505] =================================================== > [ 103.790509] [ INFO: suspicious rcu_dereference_check() usage. ] > [ 103.790511] --------------------------------------------------- > [ 103.790514] kernel/cgroup.c:4432 invoked rcu_dereference_check() without protection! > [ 103.790517] > [ 103.790517] other info that might help us debug this: > [ 103.790519] > [ 103.790521] > [ 103.790521] rcu_scheduler_active = 1, debug_locks = 1 > [ 103.790524] 4 locks held by bash/4422: > [ 103.790526] #0: (&buffer->mutex){+.+.+.}, at: [] sysfs_write_file+0x3c/0x144 > [ 103.790537] #1: (s_active#102){.+.+.+}, at: [] sysfs_write_file+0xe7/0x144 > [ 103.790544] #2: (&q->sysfs_lock){+.+.+.}, at: [] queue_attr_store+0x49/0x8f > [ 103.790552] #3: (&(&blkcg->lock)->rlock){......}, at: [] blkiocg_add_blkio_group+0x2b/0xad > [ 103.790560] > [ 103.790561] stack backtrace: > [ 103.790564] Pid: 4422, comm: bash Not tainted 2.6.34-rc4-blkio-second-crash #81 > [ 103.790567] Call Trace: > [ 103.790572] [] lockdep_rcu_dereference+0x9d/0xa5 > [ 103.790577] [] css_id+0x44/0x57 > [ 103.790581] [] blkiocg_add_blkio_group+0x53/0xad > [ 103.790586] [] cfq_init_queue+0x139/0x32c > [ 103.790591] [] elv_iosched_store+0xbf/0x1bf > [ 103.790595] [] queue_attr_store+0x70/0x8f > [ 103.790599] [] ? sysfs_write_file+0xe7/0x144 > [ 103.790603] [] sysfs_write_file+0x108/0x144 > [ 103.790609] [] vfs_write+0xae/0x10b > [ 103.790612] [] ? trace_hardirqs_on_caller+0x10c/0x130 > [ 103.790616] [] sys_write+0x4a/0x6e > [ 103.790622] [] system_call_fastpath+0x16/0x1b > [ 103.790625] > > Signed-off-by: Vivek Goyal > --- > block/cfq-iosched.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 002a5b6..9386bf8 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -3741,8 +3741,10 @@ static void *cfq_init_queue(struct request_queue *q) > * to make sure that cfq_put_cfqg() does not try to kfree root group > */ > atomic_set(&cfqg->ref, 1); > + rcu_read_lock(); > blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg, (void *)cfqd, > 0); > + rcu_read_unlock(); > #endif > /* > * Not strictly needed (since RB_ROOT just clears the node and we > -- > 1.6.2.5 >