From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161402Ab3LFWEo (ORCPT ); Fri, 6 Dec 2013 17:04:44 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:32821 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759493Ab3LFVyA (ORCPT ); Fri, 6 Dec 2013 16:54:00 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tomoki Sekiyama , Jens Axboe Subject: [PATCH 3.10 54/58] elevator: Fix a race in elevator switching and md device initialization Date: Fri, 6 Dec 2013 13:52:25 -0800 Message-Id: <20131206214849.888681560@linuxfoundation.org> X-Mailer: git-send-email 1.8.5.1.67.gb00d244 In-Reply-To: <20131206214844.906193530@linuxfoundation.org> References: <20131206214844.906193530@linuxfoundation.org> User-Agent: quilt/0.60-8.1.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tomoki Sekiyama commit eb1c160b22655fd4ec44be732d6594fd1b1e44f4 upstream. The soft lockup below happens at the boot time of the system using dm multipath and the udev rules to switch scheduler. [ 356.127001] BUG: soft lockup - CPU#3 stuck for 22s! [sh:483] [ 356.127001] RIP: 0010:[] [] lock_timer_base.isra.35+0x1d/0x50 ... [ 356.127001] Call Trace: [ 356.127001] [] try_to_del_timer_sync+0x20/0x70 [ 356.127001] [] ? kmem_cache_alloc_node_trace+0x20a/0x230 [ 356.127001] [] del_timer_sync+0x52/0x60 [ 356.127001] [] cfq_exit_queue+0x32/0xf0 [ 356.127001] [] elevator_exit+0x2f/0x50 [ 356.127001] [] elevator_change+0xf1/0x1c0 [ 356.127001] [] elv_iosched_store+0x20/0x50 [ 356.127001] [] queue_attr_store+0x59/0xb0 [ 356.127001] [] sysfs_write_file+0xc6/0x140 [ 356.127001] [] vfs_write+0xbd/0x1e0 [ 356.127001] [] SyS_write+0x49/0xa0 [ 356.127001] [] system_call_fastpath+0x16/0x1b This is caused by a race between md device initialization by multipathd and shell script to switch the scheduler using sysfs. - multipathd: SyS_ioctl -> do_vfs_ioctl -> dm_ctl_ioctl -> ctl_ioctl -> table_load -> dm_setup_md_queue -> blk_init_allocated_queue -> elevator_init q->elevator = elevator_alloc(q, e); // not yet initialized - sh -c 'echo deadline > /sys/$DEVPATH/queue/scheduler': elevator_switch (in the call trace above) struct elevator_queue *old = q->elevator; q->elevator = elevator_alloc(q, new_e); elevator_exit(old); // lockup! (*) - multipathd: (cont.) err = e->ops.elevator_init_fn(q); // init fails; q->elevator is modified (*) When del_timer_sync() is called, lock_timer_base() will loop infinitely while timer->base == NULL. In this case, as timer will never initialized, it results in lockup. This patch introduces acquisition of q->sysfs_lock around elevator_init() into blk_init_allocated_queue(), to provide mutual exclusion between initialization of the q->scheduler and switching of the scheduler. This should fix this bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=902012 Signed-off-by: Tomoki Sekiyama Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-core.c | 10 +++++++++- block/elevator.c | 6 ++++++ 2 files changed, 15 insertions(+), 1 deletion(-) --- a/block/blk-core.c +++ b/block/blk-core.c @@ -741,9 +741,17 @@ blk_init_allocated_queue(struct request_ q->sg_reserved_size = INT_MAX; + /* Protect q->elevator from elevator_change */ + mutex_lock(&q->sysfs_lock); + /* init elevator */ - if (elevator_init(q, NULL)) + if (elevator_init(q, NULL)) { + mutex_unlock(&q->sysfs_lock); return NULL; + } + + mutex_unlock(&q->sysfs_lock); + return q; } EXPORT_SYMBOL(blk_init_allocated_queue); --- a/block/elevator.c +++ b/block/elevator.c @@ -186,6 +186,12 @@ int elevator_init(struct request_queue * struct elevator_type *e = NULL; int err; + /* + * q->sysfs_lock must be held to provide mutual exclusion between + * elevator_switch() and here. + */ + lockdep_assert_held(&q->sysfs_lock); + if (unlikely(q->elevator)) return 0;