From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH 2/2] dm: stay in blk_queue_bypass until queue becomes initialized Date: Fri, 26 Oct 2012 16:21:06 -0400 Message-ID: <20121026202105.GF24687@redhat.com> References: <50890937.7010809@ce.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <50890937.7010809@ce.jp.nec.com> Sender: linux-kernel-owner@vger.kernel.org To: Jun'ichi Nomura Cc: "linux-kernel@vger.kernel.org" , device-mapper development , Tejun Heo , Jens Axboe , Alasdair G Kergon List-Id: dm-devel.ids On Thu, Oct 25, 2012 at 06:41:11PM +0900, Jun'ichi Nomura wrote: > [PATCH] dm: stay in blk_queue_bypass until queue becomes initialized > > With 749fefe677 ("block: lift the initial queue bypass mode on > blk_register_queue() instead of blk_init_allocated_queue()"), > add_disk() eventually calls blk_queue_bypass_end(). > This change invokes the following warning when multipath is used. > > BUG: scheduling while atomic: multipath/2460/0x00000002 > 1 lock held by multipath/2460: > #0: (&md->type_lock){......}, at: [] dm_lock_md_type+0x17/0x19 [dm_mod] > Modules linked in: ... > Pid: 2460, comm: multipath Tainted: G W 3.7.0-rc2 #1 > Call Trace: > [] __schedule_bug+0x6a/0x78 > [] __schedule+0xb4/0x5e0 > [] schedule+0x64/0x66 > [] schedule_timeout+0x39/0xf8 > [] ? put_lock_stats+0xe/0x29 > [] ? lock_release_holdtime+0xb6/0xbb > [] wait_for_common+0x9d/0xee > [] ? try_to_wake_up+0x206/0x206 > [] ? kfree_call_rcu+0x1c/0x1c > [] wait_for_completion+0x1d/0x1f > [] wait_rcu_gp+0x5d/0x7a > [] ? wait_rcu_gp+0x7a/0x7a > [] ? complete+0x21/0x53 > [] synchronize_rcu+0x1e/0x20 > [] blk_queue_bypass_start+0x5d/0x62 > [] blkcg_activate_policy+0x73/0x270 > [] ? kmem_cache_alloc_node_trace+0xc7/0x108 > [] cfq_init_queue+0x80/0x28e > [] ? dm_blk_ioctl+0xa7/0xa7 [dm_mod] > [] elevator_init+0xe1/0x115 > [] ? blk_queue_make_request+0x54/0x59 > [] blk_init_allocated_queue+0x8c/0x9e > [] dm_setup_md_queue+0x36/0xaa [dm_mod] > [] table_load+0x1bd/0x2c8 [dm_mod] > [] ctl_ioctl+0x1d6/0x236 [dm_mod] > [] ? table_clear+0xaa/0xaa [dm_mod] > [] dm_ctl_ioctl+0x13/0x17 [dm_mod] > [] do_vfs_ioctl+0x3fb/0x441 > [] ? file_has_perm+0x8a/0x99 > [] sys_ioctl+0x5e/0x82 > [] ? trace_hardirqs_on_thunk+0x3a/0x3f > [] system_call_fastpath+0x16/0x1b > > The warning means during queue initialization blk_queue_bypass_start() > calls sleeping function (synchronize_rcu) while dm holds md->type_lock. md->type_lock is a mutex, isn't it? I thought we are allowed to block and schedule out under mutex? add_disk() also calls disk_alloc_events() which does kzalloc(GFP_KERNEL). So we already have code which can block/wait under md->type_lock. I am not sure why should we get this warning under a mutex. Thanks Vivek