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Date: Tue, 20 Oct 2020 09:15:59 +0200
From: Paolo Valente <paolo.valente@...aro.org>
To: Mike Galbraith <efault@....de>
Cc: LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: block, bfq: lockdep circular locking dependency gripe
Hi,
that's apparently hard to solve inside bfq. The the ioc of the task is being exited while the task is still inside the code for having an I/O request served. Is still normal?
Thanks,
Polo
> Il giorno 20 ott 2020, alle ore 08:15, Mike Galbraith <efault@....de> ha scritto:
>
> [ 1917.361401] ======================================================
> [ 1917.361406] WARNING: possible circular locking dependency detected
> [ 1917.361413] 5.9.0.g7cf726a-master #2 Tainted: G S E
> [ 1917.361417] ------------------------------------------------------
> [ 1917.361422] kworker/u16:35/15995 is trying to acquire lock:
> [ 1917.361428] ffff89232237f7e0 (&ioc->lock){..-.}-{2:2}, at: put_io_context+0x30/0x90
> [ 1917.361440]
> but task is already holding lock:
> [ 1917.361445] ffff892244d2cc08 (&bfqd->lock){-.-.}-{2:2}, at: bfq_insert_requests+0x89/0x680
> [ 1917.361456]
> which lock already depends on the new lock.
>
> [ 1917.361463]
> the existing dependency chain (in reverse order) is:
> [ 1917.361469]
> -> #1 (&bfqd->lock){-.-.}-{2:2}:
> [ 1917.361479] _raw_spin_lock_irqsave+0x3d/0x50
> [ 1917.361484] bfq_exit_icq_bfqq+0x48/0x3f0
> [ 1917.361489] bfq_exit_icq+0x13/0x20
> [ 1917.361494] put_io_context_active+0x55/0x80
> [ 1917.361499] do_exit+0x72c/0xca0
> [ 1917.361504] do_group_exit+0x47/0xb0
> [ 1917.361508] __x64_sys_exit_group+0x14/0x20
> [ 1917.361513] do_syscall_64+0x33/0x40
> [ 1917.361518] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 1917.361523]
> -> #0 (&ioc->lock){..-.}-{2:2}:
> [ 1917.361532] __lock_acquire+0x149d/0x1a70
> [ 1917.361537] lock_acquire+0x1a7/0x3b0
> [ 1917.361542] _raw_spin_lock_irqsave+0x3d/0x50
> [ 1917.361547] put_io_context+0x30/0x90
> [ 1917.361552] blk_mq_free_request+0x4f/0x140
> [ 1917.361557] blk_attempt_req_merge+0x19/0x30
> [ 1917.361563] elv_attempt_insert_merge+0x4f/0x90
> [ 1917.361568] blk_mq_sched_try_insert_merge+0x28/0x40
> [ 1917.361574] bfq_insert_requests+0x94/0x680
> [ 1917.361579] blk_mq_sched_insert_requests+0xd1/0x2a0
> [ 1917.361584] blk_mq_flush_plug_list+0x12d/0x240
> [ 1917.361589] blk_flush_plug_list+0xb4/0xd0
> [ 1917.361594] io_schedule_prepare+0x3c/0x40
> [ 1917.361599] io_schedule+0xb/0x40
> [ 1917.361604] blk_mq_get_tag+0x13a/0x250
> [ 1917.361608] __blk_mq_alloc_request+0x5c/0x130
> [ 1917.361613] blk_mq_submit_bio+0xf3/0x770
> [ 1917.361618] submit_bio_noacct+0x41e/0x4b0
> [ 1917.361622] submit_bio+0x33/0x160
> [ 1917.361644] ext4_io_submit+0x49/0x60 [ext4]
> [ 1917.361661] ext4_writepages+0x683/0x1070 [ext4]
> [ 1917.361667] do_writepages+0x3c/0xe0
> [ 1917.361672] __writeback_single_inode+0x62/0x630
> [ 1917.361677] writeback_sb_inodes+0x218/0x4d0
> [ 1917.361681] __writeback_inodes_wb+0x5f/0xc0
> [ 1917.361686] wb_writeback+0x283/0x490
> [ 1917.361691] wb_workfn+0x29a/0x670
> [ 1917.361696] process_one_work+0x283/0x620
> [ 1917.361701] worker_thread+0x39/0x3f0
> [ 1917.361706] kthread+0x152/0x170
> [ 1917.361711] ret_from_fork+0x1f/0x30
> [ 1917.361715]
> other info that might help us debug this:
>
> [ 1917.361722] Possible unsafe locking scenario:
>
> [ 1917.361728] CPU0 CPU1
> [ 1917.361731] ---- ----
> [ 1917.361736] lock(&bfqd->lock);
> [ 1917.361740] lock(&ioc->lock);
> [ 1917.361746] lock(&bfqd->lock);
> [ 1917.361752] lock(&ioc->lock);
> [ 1917.361757]
> *** DEADLOCK ***
>
> [ 1917.361763] 5 locks held by kworker/u16:35/15995:
> [ 1917.361767] #0: ffff892240c9bd38 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x1fa/0x620
> [ 1917.361778] #1: ffff94569342fe78 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x1fa/0x620
> [ 1917.361789] #2: ffff8921424ae0e0 (&type->s_umount_key#39){++++}-{3:3}, at: trylock_super+0x16/0x50
> [ 1917.361800] #3: ffff8921424aaa40 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: do_writepages+0x3c/0xe0
> [ 1917.361811] #4: ffff892244d2cc08 (&bfqd->lock){-.-.}-{2:2}, at: bfq_insert_requests+0x89/0x680
> [ 1917.361821]
> stack backtrace:
> [ 1917.361827] CPU: 6 PID: 15995 Comm: kworker/u16:35 Kdump: loaded Tainted: G S E 5.9.0.g7cf726a-master #2
> [ 1917.361833] Hardware name: MEDION MS-7848/MS-7848, BIOS M7848W08.20C 09/23/2013
> [ 1917.361840] Workqueue: writeback wb_workfn (flush-8:32)
> [ 1917.361846] Call Trace:
> [ 1917.361854] dump_stack+0x77/0x97
> [ 1917.361860] check_noncircular+0xe7/0x100
> [ 1917.361866] ? __lock_acquire+0x2ce/0x1a70
> [ 1917.361872] ? __lock_acquire+0x149d/0x1a70
> [ 1917.361877] __lock_acquire+0x149d/0x1a70
> [ 1917.361884] lock_acquire+0x1a7/0x3b0
> [ 1917.361889] ? put_io_context+0x30/0x90
> [ 1917.361894] ? bfq_put_queue+0xcf/0x480
> [ 1917.361901] _raw_spin_lock_irqsave+0x3d/0x50
> [ 1917.361906] ? put_io_context+0x30/0x90
> [ 1917.361911] put_io_context+0x30/0x90
> [ 1917.361916] blk_mq_free_request+0x4f/0x140
> [ 1917.361921] blk_attempt_req_merge+0x19/0x30
> [ 1917.361926] elv_attempt_insert_merge+0x4f/0x90
> [ 1917.361932] blk_mq_sched_try_insert_merge+0x28/0x40
> [ 1917.361937] bfq_insert_requests+0x94/0x680
> [ 1917.361944] blk_mq_sched_insert_requests+0xd1/0x2a0
> [ 1917.361950] blk_mq_flush_plug_list+0x12d/0x240
> [ 1917.361956] blk_flush_plug_list+0xb4/0xd0
> [ 1917.361962] io_schedule_prepare+0x3c/0x40
> [ 1917.361967] io_schedule+0xb/0x40
> [ 1917.361972] blk_mq_get_tag+0x13a/0x250
> [ 1917.361978] ? wait_woken+0xa0/0xa0
> [ 1917.361984] __blk_mq_alloc_request+0x5c/0x130
> [ 1917.361989] blk_mq_submit_bio+0xf3/0x770
> [ 1917.361996] submit_bio_noacct+0x41e/0x4b0
> [ 1917.362002] ? submit_bio+0x33/0x160
> [ 1917.362007] submit_bio+0x33/0x160
> [ 1917.362028] ext4_io_submit+0x49/0x60 [ext4]
> [ 1917.362045] ext4_writepages+0x683/0x1070 [ext4]
> [ 1917.362056] ? do_writepages+0x3c/0xe0
> [ 1917.362060] do_writepages+0x3c/0xe0
> [ 1917.362067] ? __writeback_single_inode+0x62/0x630
> [ 1917.362072] __writeback_single_inode+0x62/0x630
> [ 1917.362078] writeback_sb_inodes+0x218/0x4d0
> [ 1917.362087] __writeback_inodes_wb+0x5f/0xc0
> [ 1917.362093] wb_writeback+0x283/0x490
> [ 1917.362100] ? wb_workfn+0x29a/0x670
> [ 1917.362104] wb_workfn+0x29a/0x670
> [ 1917.362112] ? process_one_work+0x283/0x620
> [ 1917.362117] ? process_one_work+0x251/0x620
> [ 1917.362121] process_one_work+0x283/0x620
> [ 1917.362128] worker_thread+0x39/0x3f0
> [ 1917.362133] ? process_one_work+0x620/0x620
> [ 1917.362138] kthread+0x152/0x170
> [ 1917.362142] ? kthread_park+0x90/0x90
> [ 1917.362148] ret_from_fork+0x1f/0x30
>
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