From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756245Ab0ECSxk (ORCPT ); Mon, 3 May 2010 14:53:40 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:43892 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755672Ab0ECSx3 (ORCPT ); Mon, 3 May 2010 14:53:29 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, Vivek Goyal , "Paul E. McKenney" , Jens Axboe Subject: [PATCH tip/core/urgent 09/10] blk-cgroup: Fix RCU correctness warning in cfq_init_queue() Date: Mon, 3 May 2010 11:53:18 -0700 Message-Id: <1272912799-17859-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.0 In-Reply-To: <20100503185253.GA17672@linux.vnet.ibm.com> References: <20100503185253.GA17672@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vivek Goyal It is necessary to be in an RCU read-side critical section when invoking css_id(), so this patch adds one to blkiocg_add_blkio_group(). This is actually a false positive, because this is called at initialization time and hence always refers to the root cgroup, which cannot go away. [ 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] Located-by: Miles Lane Signed-off-by: Vivek Goyal Signed-off-by: Paul E. McKenney Cc: Jens Axboe --- 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 838834b..5f127cf 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3694,8 +3694,10 @@ 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 -- 1.7.0