Re: [tip:locking/core] locking/ww_mutex: Add kselftests for ww_mutex stress

[Peter Zijlstra]

Hi Chris,

I got me this... I'm still trying to wrap my head around what exactly
the test does.

=====================================
[ BUG: bad unlock balance detected! ]
4.10.0-rc4-00122-g6edad167-dirty #608 Not tainted
-------------------------------------
kworker/u81:37/330 is trying to release lock (ww_class_mutex) at:
[<ffffffff8115260a>] stress_inorder_work+0x15a/0x330
but there are no more locks to release!

other info that might help us debug this:
4 locks held by kworker/u81:37/330:
 #0:  ("test-ww_mutex"){++++.+}, at: [<ffffffff81111d62>] process_one_work+0x1f2/0x710
 #1:  ((&stress->work)){+.+.+.}, at: [<ffffffff81111d62>] process_one_work+0x1f2/0x710
 #2:  (ww_class_acquire){+.+...}, at: [<ffffffff81111ddd>] process_one_work+0x26d/0x710
 #3:  (ww_class_mutex){+.+...}, at: [<ffffffff811525ba>] stress_inorder_work+0x10a/0x330

stack backtrace:
CPU: 22 PID: 330 Comm: kworker/u81:37 Not tainted 4.10.0-rc4-00122-g6edad167-dirty #608
Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
Workqueue: test-ww_mutex stress_inorder_work
Call Trace:
 dump_stack+0x86/0xc3
 ? stress_inorder_work+0x15a/0x330
 print_unlock_imbalance_bug+0xd8/0xe0
 ? stress_inorder_work+0x15a/0x330
 lock_release+0x374/0x4b0
 ? schedule_hrtimeout_range_clock+0xda/0x270
 __mutex_unlock_slowpath+0x43/0x2e0
 ww_mutex_unlock+0x47/0xb0
 stress_inorder_work+0x15a/0x330
 ? process_one_work+0x26d/0x710
 process_one_work+0x26d/0x710
 ? process_one_work+0x1f2/0x710
 worker_thread+0x48/0x4e0
 kthread+0x101/0x140
 ? process_one_work+0x710/0x710
 ? kthread_create_on_node+0x40/0x40
 ret_from_fork+0x31/0x40
INFO: task swapper/0:1 blocked for more than 120 seconds.
      Not tainted 4.10.0-rc4-00122-g6edad167-dirty #608
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
swapper/0       D    0     1      0 0x00000000
Call Trace:
 __schedule+0x30a/0xc60
 schedule+0x40/0x90
 schedule_timeout+0x30a/0x670
 ? wait_for_completion+0x23/0x100
 ? trace_hardirqs_on_caller+0x100/0x1c0
 wait_for_completion+0x97/0x100
 ? wake_up_q+0x70/0x70
 flush_workqueue+0x1f6/0x6b0
 ? flush_workqueue+0xe8/0x6b0
 stress+0x1b3/0x203
 test_ww_mutex_init+0x30a/0x324
 ? __pv_init_lock_hash+0x59/0x59
 ? set_debug_rodata+0x12/0x12
 do_one_initcall+0x43/0x180
 ? set_debug_rodata+0x12/0x12
 kernel_init_freeable+0x1d9/0x266
 ? rest_init+0x140/0x140
 kernel_init+0xe/0x100
 ret_from_fork+0x31/0x40
INFO: lockdep is turned off. +