Hi all,
I've noticed that sometimes lockdep would spew a warning and an oops
while dumping the list of held locks. I'm not quite sure why it happens
and I didn't find anything that was recently changed in the code that
could cause that:
[ 855.807172] Showing all locks held in the system:
[ 855.809162] 2 locks held by khungtaskd/3552:
[ 855.809729] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff811c3563>]
watchdog+0x73/0x490
[ 855.810956] #1: (tasklist_lock){.+.+..}, at: [<ffffffff8118c58c>]
debug_show_all_locks+0x5c/0x260
[ 855.815299] 1 lock held by ksmd/3578:
[ 855.815770] #0: (ksm_thread_mutex){+.+.+.}, at: [<ffffffff8126653e>]
ksm_scan_thread+0x4e/0x310
[ 855.817055] 2 locks held by kpktgend_5/7480:
[ 855.817597] #0: (rcu_read_lock){.+.+..}, at: [< (null)>]
(null)
[ 855.821794] #1:
[ 855.822044] ------------[ cut here ]------------
[ 855.822677] WARNING: at kernel/lockdep.c:146 hlock_class+0x50/0x80()
[ 855.823477] DEBUG_LOCKS_WARN_ON(1)
[ 855.827953] Modules linked in:
[ 855.828423] CPU: 1 PID: 3552 Comm: khungtaskd Tainted: G W
3.9.0-rc8-next-20130423-sasha-00014-gdf37a98 #352
[ 855.829749] 0000000000000009 ffff8800b8e05c28 ffffffff83fb6095
ffff8800b8e05c68
[ 855.830798] ffffffff811142db 00000000b58a3000 ffff8800adee0950
0000000000000002
[ 855.835860] 0000000000000002 ffff8800b58a3000 ffff8800afa18000
ffff8800b8e05cc8
[ 855.836887] Call Trace:
[ 855.837222] [<ffffffff83fb6095>] dump_stack+0x19/0x1b
[ 855.840950] [<ffffffff811142db>] warn_slowpath_common+0x6b/0xa0
[ 855.841734] [<ffffffff811143b1>] warn_slowpath_fmt+0x41/0x50
[ 855.842472] [<ffffffff83faa137>] ? printk+0x48/0x4a
[ 855.843106] [<ffffffff811881f0>] hlock_class+0x50/0x80
[ 855.843758] [<ffffffff83fab453>] print_lock+0xe/0x3d
[ 855.847471] [<ffffffff81189c92>] lockdep_print_held_locks+0xa2/0xe0
[ 855.848561] [<ffffffff8118c64a>] debug_show_all_locks+0x11a/0x260
[ 855.849351] [<ffffffff8115a427>] show_state_filter+0x207/0x220
[ 855.850141] [<ffffffff8115a220>] ? sched_show_task+0x270/0x270
[ 855.853945] [<ffffffff81189c92>] ? lockdep_print_held_locks+0xa2/0xe0
[ 855.854756] [<ffffffff8115a052>] ? sched_show_task+0xa2/0x270
[ 855.855476] [<ffffffff811c3803>] watchdog+0x313/0x490
[ 855.856107] [<ffffffff811c3563>] ? watchdog+0x73/0x490
[ 855.856739] [<ffffffff811c34f0>] ? hung_task_panic+0x20/0x20
[ 855.862510] [<ffffffff81146673>] kthread+0xe3/0xf0
[ 855.863119] [<ffffffff81146590>] ? kthread_create_on_node+0x160/0x160
[ 855.863917] [<ffffffff83fff1fc>] ret_from_fork+0x7c/0xb0
[ 855.864575] [<ffffffff81146590>] ? kthread_create_on_node+0x160/0x160
[ 855.868426] ---[ end trace 3adc9bd194fdba9a ]---
[ 855.869001] BUG: unable to handle kernel NULL pointer dereference at
0000000000000030
[ 855.869983] IP: [<ffffffff81189a70>] __print_lock_name+0xc0/0xc0
[ 855.870744] PGD 0
[ 855.872483] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 855.872483] Dumping ftrace buffer:
[ 855.872483] (ftrace buffer empty)
[ 855.872483] Modules linked in:
[ 855.872483] CPU: 1 PID: 3552 Comm: khungtaskd Tainted: G W
3.9.0-rc8-next-20130423-sasha-00014-gdf37a98 #352
[ 855.872483] task: ffff8800b58a3000 ti: ffff8800b8e04000 task.ti:
ffff8800b8e04000
[ 855.872483] RIP: 0010:[<ffffffff81189a70>] [<ffffffff81189a70>]
__print_lock_name+0xc0/0xc0
[ 855.872483] RSP: 0018:ffff8800b8e05cb0 EFLAGS: 00010296
[ 855.872483] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000008a728a71
[ 855.872483] RDX: ffff8800b58a3000 RSI: ffff8800b8e05cc1 RDI: 0000000000000000
[ 855.872483] RBP: ffff8800b8e05cd8 R08: 0000000000000002 R09: 0000000000000000
[ 855.872483] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
[ 855.890101] R13: 0000000000000002 R14: ffff8800b58a3000 R15: ffff8800afa18000
[ 855.891151] FS: 0000000000000000(0000) GS:ffff8800bb600000(0000)
knlGS:0000000000000000
[ 855.891151] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 855.891151] CR2: 0000000000000030 CR3: 0000000005826000 CR4: 00000000000406e0
[ 855.891151] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 855.891151] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 855.891151] Stack:
[ 855.891151] ffffffff81189bb5 0000000000000002 0000000000000002
ffff8800b8e05cd8
[ 855.891151] ffff8800adee0950 ffff8800b8e05cf8 ffffffff83fab45b
0000000000000038
[ 855.891151] ffff8800adee0000 ffff8800b8e05d28 ffffffff81189c92
ffff8800b8e05d28
[ 855.891151] Call Trace:
[ 855.891151] [<ffffffff81189bb5>] ? print_lock_name+0x15/0x50
[ 855.891151] [<ffffffff83fab45b>] print_lock+0x16/0x3d
[ 855.891151] [<ffffffff81189c92>] lockdep_print_held_locks+0xa2/0xe0
[ 855.891151] [<ffffffff8118c64a>] debug_show_all_locks+0x11a/0x260
[ 855.891151] [<ffffffff8115a427>] show_state_filter+0x207/0x220
[ 855.900353] [<ffffffff8115a220>] ? sched_show_task+0x270/0x270
[ 855.900353] [<ffffffff81189c92>] ? lockdep_print_held_locks+0xa2/0xe0
[ 855.900353] [<ffffffff8115a052>] ? sched_show_task+0xa2/0x270
[ 855.900353] [<ffffffff811c3803>] watchdog+0x313/0x490
[ 855.900353] [<ffffffff811c3563>] ? watchdog+0x73/0x490
[ 855.900353] [<ffffffff811c34f0>] ? hung_task_panic+0x20/0x20
[ 855.900353] [<ffffffff81146673>] kthread+0xe3/0xf0
[ 855.900353] [<ffffffff81146590>] ? kthread_create_on_node+0x160/0x160
[ 855.900353] [<ffffffff83fff1fc>] ret_from_fork+0x7c/0xb0
[ 855.900353] [<ffffffff81146590>] ? kthread_create_on_node+0x160/0x160
[ 855.900353] Code: 0f 1f 00 48 8b 45 e8 65 48 33 04 25 28 00 00 00 74 09 e8
d4 a6 f8 ff 0f 1f 40 00 48 81 c4 98 00 00 00 5b 5d
c3 66 0f 1f 44 00 00 <48> 8b 47 30 55 48 89 e5 a8 04 0f 85 a3 00 00 00 83 e0 01
f7 d8
[ 855.900353] RIP [<ffffffff81189a70>] __print_lock_name+0xc0/0xc0
[ 855.900353] RSP <ffff8800b8e05cb0>
[ 855.900353] CR2: 0000000000000030
[ 856.494698] ---[ end trace 3adc9bd194fdba9b ]---
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