On 8/10/22 05:34, Vlastimil Babka wrote:
On 8/9/22 22:59, Waiman Long wrote:
A circular locking problem is reported by lockdep due to the following
circular locking dependency.
+--> cpu_hotplug_lock --> slab_mutex --> kn->active#126 --+
| |
+---------------------------------------------------------+
This sounded familiar and I've found a thread from January:
https://lore.kernel.org/all/388098b2c03fbf0a732834fc01b2d875c335bc49.1642170196.git.lucien.xin@xxxxxxxxx/
But that seemed to be specific to RHEL-8 RT kernel and not reproduced
with mainline. Is it different this time? Can you share the splats?
I think this is easier to reproduce on a RT kernel, but it also happens
in a non-RT kernel. One example splat that I got was
[ 1777.114757] ======================================================
[ 1777.121646] WARNING: possible circular locking dependency detected
[ 1777.128544] 4.18.0-403.el8.x86_64+debug #1 Not tainted
[ 1777.134280] ------------------------------------------------------
[ 1777.141176] slub_cpu_partia/4113 is trying to acquire lock:
[ 1777.147395] ffffffffaef95b20 (cpu_hotplug_lock){++++}-{0:0}, at:
cpu_partial_store+0x47/0xa0
[ 1777.156837]
but task is already holding lock:
[ 1777.163346] ffff88811bd17578 (kn->count#126){++++}-{0:0}, at:
kernfs_fop_write+0x1d0/0x410
[ 1777.172591]
which lock already depends on the new lock.
[ 1777.181718]
the existing dependency chain (in reverse order) is:
[ 1777.190070]
-> #2 (kn->count#126){++++}-{0:0}:
[ 1777.196688] lock_acquire+0x1db/0x8e0
[ 1777.201360] __kernfs_remove+0x617/0x800
[ 1777.206320] kernfs_remove+0x1d/0x30
[ 1777.210891] kobject_del+0x8e/0x150
[ 1777.215360] kmem_cache_destroy+0x10d/0x130
[ 1777.220615] bioset_exit+0x1e3/0x2c0
[ 1777.225189] blk_release_queue+0x20d/0x310
[ 1777.230336] kobject_release+0x105/0x390
[ 1777.235296] scsi_device_dev_release_usercontext+0x5e3/0xd60
[ 1777.242198] execute_in_process_context+0x27/0x130
[ 1777.248131] device_release+0xa1/0x210
[ 1777.252899] kobject_release+0x105/0x390
[ 1777.257857] scsi_alloc_sdev+0xa1e/0xc80
[ 1777.262820] scsi_probe_and_add_lun+0x809/0x2da0
[ 1777.268557] __scsi_scan_target+0x1c1/0xb60
[ 1777.273801] scsi_scan_channel+0xe2/0x150
[ 1777.278855] scsi_scan_host_selected+0x1fb/0x2a0
[ 1777.284590] do_scan_async+0x3e/0x440
[ 1777.289258] async_run_entry_fn+0xd8/0x660
[ 1777.294413] process_one_work+0x919/0x17c0
[ 1777.299568] worker_thread+0x87/0xb40
[ 1777.304227] kthread+0x30d/0x3c0
[ 1777.308411] ret_from_fork+0x3a/0x50
[ 1777.312984]
-> #1 (slab_mutex){+.+.}-{3:3}:
[ 1777.319309] lock_acquire+0x1db/0x8e0
[ 1777.323978] __mutex_lock+0x154/0x15d0
[ 1777.328745] kmem_cache_destroy+0x3f/0x130
[ 1777.333898] bioset_exit+0x1e3/0x2c0
[ 1777.338469] blk_release_queue+0x20d/0x310
[ 1777.343623] kobject_release+0x105/0x390
[ 1777.348582] scsi_device_dev_release_usercontext+0x5e3/0xd60
[ 1777.355481] execute_in_process_context+0x27/0x130
[ 1777.361409] device_release+0xa1/0x210
[ 1777.366175] kobject_release+0x105/0x390
[ 1777.371135] scsi_alloc_sdev+0xa1e/0xc80
[ 1777.376096] scsi_probe_and_add_lun+0x809/0x2da0
[ 1777.381824] __scsi_scan_target+0x1c1/0xb60
[ 1777.387073] scsi_scan_channel+0xe2/0x150
[ 1777.392128] scsi_scan_host_selected+0x1fb/0x2a0
[ 1777.397864] do_scan_async+0x3e/0x440
[ 1777.402533] async_run_entry_fn+0xd8/0x660
[ 1777.407688] process_one_work+0x919/0x17c0
[ 1777.412841] worker_thread+0x87/0xb40
[ 1777.417509] kthread+0x30d/0x3c0
[ 1777.421693] ret_from_fork+0x3a/0x50
[ 1777.426263]
-> #0 (cpu_hotplug_lock){++++}-{0:0}:
[ 1777.433168] check_prevs_add+0x3fa/0x18b0
[ 1777.438226] __lock_acquire+0x21b3/0x2b80
[ 1777.443273] lock_acquire+0x1db/0x8e0
[ 1777.447940] cpus_read_lock+0x40/0xc0
[ 1777.452611] cpu_partial_store+0x47/0xa0
[ 1777.457571] slab_attr_store+0x20/0x30
[ 1777.462338] kernfs_fop_write+0x255/0x410
[ 1777.467394] vfs_write+0x157/0x460
[ 1777.471777] ksys_write+0xb8/0x170
[ 1777.476155] do_syscall_64+0xa5/0x450
[ 1777.480828] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 1777.487041]
other info that might help us debug this:
[ 1777.495975] Chain exists of:
cpu_hotplug_lock --> slab_mutex --> kn->count#126
[ 1777.507443] Possible unsafe locking scenario:
[ 1777.514049] CPU0 CPU1
[ 1777.519102] ---- ----
[ 1777.524155] lock(kn->count#126);
[ 1777.527956] lock(slab_mutex);
[ 1777.534274] lock(kn->count#126);
[ 1777.540885] lock(cpu_hotplug_lock);
[ 1777.544964]
*** DEADLOCK ***
[ 1777.551570] 3 locks held by slub_cpu_partia/4113:
[ 1777.556820] #0: ffff8881319884d0 (sb_writers#4){.+.+}-{0:0}, at:
vfs_write+0x31c/0x460
[ 1777.565771] #1: ffff888161d39490 (&of->mutex){+.+.}-{3:3}, at:
kernfs_fop_write+0x1ad/0x410
[ 1777.575203] #2: ffff88811bd17578 (kn->count#126){++++}-{0:0}, at:
kernfs_fop_write+0x1d0/0x410
[ 1777.584928]
stack backtrace:
[ 1777.589792] CPU: 65 PID: 4113 Comm: slub_cpu_partia Kdump: loaded Not
tainted 4.18.0-403.el8.x86_64+debug #1
[ 1777.600767] Hardware name: Lenovo ThinkSystem SR635
-[7Y98XXXXXX]-/System Board, BIOS CFE103A 07/04/2019
[ 1777.611342] Call Trace:
[ 1777.614072] dump_stack+0x5c/0x80
[ 1777.617777] check_noncircular+0x27f/0x320
[ 1777.622352] ? print_circular_bug+0x440/0x440
[ 1777.627215] ? kernel_text_address+0x125/0x140
[ 1777.632170] ? mark_lock.part.31+0xf4/0xd40
[ 1777.636841] ? is_dynamic_key+0x220/0x220
[ 1777.641326] check_prevs_add+0x3fa/0x18b0
[ 1777.645798] ? sched_clock+0x5/0x10
[ 1777.649695] ? sched_clock_cpu+0x18/0x1e0
[ 1777.654175] ? check_irq_usage+0xa20/0xa20
[ 1777.658750] ? find_held_lock+0x1c0/0x1c0
[ 1777.663225] ? sched_clock_cpu+0x18/0x1e0
[ 1777.667705] __lock_acquire+0x21b3/0x2b80
[ 1777.672192] lock_acquire+0x1db/0x8e0
[ 1777.676279] ? cpu_partial_store+0x47/0xa0
[ 1777.680854] ? rcu_read_unlock+0x50/0x50
[ 1777.685239] ? sysfs_file_ops+0x160/0x160
[ 1777.689718] cpus_read_lock+0x40/0xc0
[ 1777.693806] ? cpu_partial_store+0x47/0xa0
[ 1777.698380] cpu_partial_store+0x47/0xa0
[ 1777.702761] slab_attr_store+0x20/0x30
[ 1777.706944] kernfs_fop_write+0x255/0x410
[ 1777.711424] vfs_write+0x157/0x460
[ 1777.715224] ksys_write+0xb8/0x170
[ 1777.719023] ? __ia32_sys_read+0xb0/0xb0
[ 1777.723406] ? lockdep_hardirqs_on_prepare+0x294/0x3e0
[ 1777.729144] ? do_syscall_64+0x22/0x450
[ 1777.733429] do_syscall_64+0xa5/0x450
[ 1777.737518] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 1777.743159] RIP: 0033:0x7f4fe9b2ead8
[ 1777.747153] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00
00 f3 0f 1e fa 48 8d 05 45 4c 2a 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f
05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
[ 1777.768112] RSP: 002b:00007ffcc2173d48 EFLAGS: 00000246 ORIG_RAX:
0000000000000001
[ 1777.776565] RAX: ffffffffffffffda RBX: 0000000000000002 RCX:
00007f4fe9b2ead8
[ 1777.784530] RDX: 0000000000000002 RSI: 000055d41293eb70 RDI:
0000000000000001
[ 1777.792495] RBP: 000055d41293eb70 R08: 000000000000000a R09:
0000000000000003
[ 1777.800459] R10: 000000000000000a R11: 0000000000000246 R12:
00007f4fe9dcf6e0
[ 1777.808425] R13: 0000000000000002 R14: 00007f4fe9dca860 R15:
0000000000000002
The cpu_partial_store() method call flush_all() which takes the
cpu_hotplug_lock completing the cycle.
Cheers,
Longman
