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SubjectRe: [PATCH v8 00/14] lockdep: Implement crossrelease feature

So with the latest fixes there's a new lockdep warning on one of my testboxes:

[ 11.322487] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)

[ 11.495661] ======================================================
[ 11.502093] WARNING: possible circular locking dependency detected
[ 11.508507] 4.13.0-rc5-00497-g73135c58-dirty #1 Not tainted
[ 11.514313] ------------------------------------------------------
[ 11.520725] umount/533 is trying to acquire lock:
[ 11.525657] ((complete)&barr->done){+.+.}, at: [<ffffffff810fdbb3>] flush_work+0x213/0x2f0
[ 11.534411]
but task is already holding lock:
[ 11.540661] (lock#3){+.+.}, at: [<ffffffff8122678d>] lru_add_drain_all_cpuslocked+0x3d/0x190
[ 11.549613]
which lock already depends on the new lock.

The full splat is below. The kernel config is nothing fancy - distro derived,
pretty close to defconfig, with lockdep enabled.

Thanks,

Ingo

[ 11.322487] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)

[ 11.495661] ======================================================
[ 11.502093] WARNING: possible circular locking dependency detected
[ 11.508507] 4.13.0-rc5-00497-g73135c58-dirty #1 Not tainted
[ 11.514313] ------------------------------------------------------
[ 11.520725] umount/533 is trying to acquire lock:
[ 11.525657] ((complete)&barr->done){+.+.}, at: [<ffffffff810fdbb3>] flush_work+0x213/0x2f0
[ 11.534411]
but task is already holding lock:
[ 11.540661] (lock#3){+.+.}, at: [<ffffffff8122678d>] lru_add_drain_all_cpuslocked+0x3d/0x190
[ 11.549613]
which lock already depends on the new lock.

[ 11.558349]
the existing dependency chain (in reverse order) is:
[ 11.566229]
-> #3 (lock#3){+.+.}:
[ 11.571439] lock_acquire+0xe7/0x1d0
[ 11.575765] __mutex_lock+0x75/0x8e0
[ 11.580086] lru_add_drain_all_cpuslocked+0x3d/0x190
[ 11.585797] lru_add_drain_all+0xf/0x20
[ 11.590402] invalidate_bdev+0x3e/0x60
[ 11.594901] ext4_put_super+0x1f9/0x3d0
[ 11.599485] generic_shutdown_super+0x64/0x110
[ 11.604685] kill_block_super+0x21/0x50
[ 11.609270] deactivate_locked_super+0x39/0x70
[ 11.614462] cleanup_mnt+0x3b/0x70
[ 11.618612] task_work_run+0x72/0x90
[ 11.622955] exit_to_usermode_loop+0x93/0xa0
[ 11.627971] do_syscall_64+0x1a2/0x1c0
[ 11.632470] return_from_SYSCALL_64+0x0/0x7a
[ 11.637487]
-> #2 (cpu_hotplug_lock.rw_sem){++++}:
[ 11.644144] lock_acquire+0xe7/0x1d0
[ 11.648487] cpus_read_lock+0x2b/0x60
[ 11.652897] apply_workqueue_attrs+0x12/0x50
[ 11.657917] __alloc_workqueue_key+0x2f2/0x510
[ 11.663110] scsi_host_alloc+0x353/0x470
[ 11.667780] _scsih_probe+0x5bb/0x7b0
[ 11.672192] local_pci_probe+0x3f/0x90
[ 11.676714] work_for_cpu_fn+0x10/0x20
[ 11.681213] process_one_work+0x1fc/0x670
[ 11.685971] worker_thread+0x219/0x3e0
[ 11.690469] kthread+0x13a/0x170
[ 11.694465] ret_from_fork+0x27/0x40
[ 11.698790]
-> #1 ((&wfc.work)){+.+.}:
[ 11.704433] worker_thread+0x219/0x3e0
[ 11.708930] kthread+0x13a/0x170
[ 11.712908] ret_from_fork+0x27/0x40
[ 11.717234] 0xffffffffffffffff
[ 11.721142]
-> #0 ((complete)&barr->done){+.+.}:
[ 11.727633] __lock_acquire+0x1433/0x14a0
[ 11.732392] lock_acquire+0xe7/0x1d0
[ 11.736715] wait_for_completion+0x4e/0x170
[ 11.741664] flush_work+0x213/0x2f0
[ 11.745919] lru_add_drain_all_cpuslocked+0x149/0x190
[ 11.751718] lru_add_drain_all+0xf/0x20
[ 11.756303] invalidate_bdev+0x3e/0x60
[ 11.760819] ext4_put_super+0x1f9/0x3d0
[ 11.765403] generic_shutdown_super+0x64/0x110
[ 11.770596] kill_block_super+0x21/0x50
[ 11.775181] deactivate_locked_super+0x39/0x70
[ 11.780372] cleanup_mnt+0x3b/0x70
[ 11.784522] task_work_run+0x72/0x90
[ 11.788848] exit_to_usermode_loop+0x93/0xa0
[ 11.793875] do_syscall_64+0x1a2/0x1c0
[ 11.798399] return_from_SYSCALL_64+0x0/0x7a
[ 11.803416]
other info that might help us debug this:

[ 11.811997] Chain exists of:
(complete)&barr->done --> cpu_hotplug_lock.rw_sem --> lock#3

[ 11.823810] Possible unsafe locking scenario:

[ 11.830120] CPU0 CPU1
[ 11.834878] ---- ----
[ 11.839636] lock(lock#3);
[ 11.842653] lock(cpu_hotplug_lock.rw_sem);
[ 11.849697] lock(lock#3);
[ 11.855236] lock((complete)&barr->done);
[ 11.859560]
*** DEADLOCK ***

[ 11.866054] 3 locks held by umount/533:
[ 11.870117] #0: (&type->s_umount_key#24){+.+.}, at: [<ffffffff8129b7ad>] deactivate_super+0x4d/0x60
[ 11.879737] #1: (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff812268ea>] lru_add_drain_all+0xa/0x20
[ 11.889445] #2: (lock#3){+.+.}, at: [<ffffffff8122678d>] lru_add_drain_all_cpuslocked+0x3d/0x190
[ 11.898805]
stack backtrace:
[ 11.903573] CPU: 12 PID: 533 Comm: umount Not tainted 4.13.0-rc5-00497-g73135c58-dirty #1
[ 11.912169] Hardware name: Supermicro H8DG6/H8DGi/H8DG6/H8DGi, BIOS 2.0b 03/01/2012
[ 11.920759] Call Trace:
[ 11.923433] dump_stack+0x5e/0x8e
[ 11.926975] print_circular_bug+0x204/0x310
[ 11.931385] ? add_lock_to_list.isra.29+0xb0/0xb0
[ 11.936316] check_prev_add+0x444/0x860
[ 11.940382] ? generic_shutdown_super+0x64/0x110
[ 11.945237] ? add_lock_to_list.isra.29+0xb0/0xb0
[ 11.950168] ? __lock_acquire+0x1433/0x14a0
[ 11.954578] __lock_acquire+0x1433/0x14a0
[ 11.958818] lock_acquire+0xe7/0x1d0
[ 11.962621] ? flush_work+0x213/0x2f0
[ 11.966506] wait_for_completion+0x4e/0x170
[ 11.970915] ? flush_work+0x213/0x2f0
[ 11.974807] ? flush_work+0x1e6/0x2f0
[ 11.978699] flush_work+0x213/0x2f0
[ 11.982416] ? flush_workqueue_prep_pwqs+0x1b0/0x1b0
[ 11.987610] ? mark_held_locks+0x66/0x90
[ 11.991778] ? queue_work_on+0x41/0x70
[ 11.995755] lru_add_drain_all_cpuslocked+0x149/0x190
[ 12.001034] lru_add_drain_all+0xf/0x20
[ 12.005124] invalidate_bdev+0x3e/0x60
[ 12.009094] ext4_put_super+0x1f9/0x3d0
[ 12.013159] generic_shutdown_super+0x64/0x110
[ 12.017856] kill_block_super+0x21/0x50
[ 12.021922] deactivate_locked_super+0x39/0x70
[ 12.026591] cleanup_mnt+0x3b/0x70
[ 12.030242] task_work_run+0x72/0x90
[ 12.034063] exit_to_usermode_loop+0x93/0xa0
[ 12.038561] do_syscall_64+0x1a2/0x1c0
[ 12.042541] entry_SYSCALL64_slow_path+0x25/0x25
[ 12.047384] RIP: 0033:0x7fc3f2854a37
[ 12.051189] RSP: 002b:00007fff660582b8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
[ 12.059162] RAX: 0000000000000000 RBX: 00000074471c14e0 RCX: 00007fc3f2854a37
[ 12.066530] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000074471c22e0
[ 12.073895] RBP: 00000074471c22e0 R08: 0000000000000000 R09: 0000000000000002
[ 12.081264] R10: 00007fff66058050 R11: 0000000000000246 R12: 00007fc3f35e6890
[ 12.088656] R13: 0000000000000000 R14: 00000074471c1660 R15: 0000000000000000
[ 12.110307] dracut: Checking ext4: /dev/sda2

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