FYI, we noticed the below changes on

https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git for-kbuild-bot/current-stable
commit 63a745aa6ac924a1dd17567e03bac83050afc8de ("ptrace: fix ptrace vs tasklist_lock race")


+-------------------------------------------------+------------+------------+
|                                                 | 722e07cda3 | 63a745aa6a |
+-------------------------------------------------+------------+------------+
| boot_successes                                  | 52         | 27         |
| boot_failures                                   | 0          | 6          |
| inconsistent{HARDIRQ-ON-W}->{IN-HARDIRQ-W}usage | 0          | 6          |
| backtrace:ptrace_check_attach                   | 0          | 6          |
| backtrace:SyS_ptrace                            | 0          | 6          |
| backtrace:cpu_startup_entry                     | 0          | 2          |
+-------------------------------------------------+------------+------------+



[   29.600508] [ INFO: inconsistent lock state ]
[   29.601341] 4.4.0-rc6-00128-g63a745a #1 Not tainted
[   29.602035] ---------------------------------
[   29.602667] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
[   29.603480] swapper/1/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
[   29.604191]  (&(&sighand->siglock)->rlock){?.+...}, at: [<ffffffff810e4d01>] __lock_task_sighand+0xb5/0x10a
[   29.605813] {HARDIRQ-ON-W} state was registered at:
[   29.606553]   [<ffffffff811151e6>] mark_held_locks+0x5e/0x74
[   29.607395]   [<ffffffff81115340>] trace_hardirqs_on_caller+0x144/0x197
[   29.608327]   [<ffffffff811153a0>] trace_hardirqs_on+0xd/0xf
[   29.609215]   [<ffffffff82e30b3b>] _raw_spin_unlock_irq+0x2c/0x3b
[   29.610149]   [<ffffffff810e0fdb>] ptrace_check_attach+0xbc/0x147
[   29.611038]   [<ffffffff810e19a2>] SyS_ptrace+0x97/0xea
[   29.611827]   [<ffffffff82e314b2>] entry_SYSCALL_64_fastpath+0x12/0x76
[   29.612807] irq event stamp: 160226
[   29.613540] hardirqs last  enabled at (160223): [<ffffffff8105f2e9>] default_idle+0x1f/0x37
[   29.614821] hardirqs last disabled at (160224): [<ffffffff82e32267>] apic_timer_interrupt+0x87/0xa0
[   29.616140] softirqs last  enabled at (160226): [<ffffffff810dc633>] _local_bh_enable+0x42/0x44
[   29.617461] softirqs last disabled at (160225): [<ffffffff810dd405>] irq_enter+0x2e/0x65
[   29.618704] 
[   29.618704] other info that might help us debug this:
[   29.619679]  Possible unsafe locking scenario:
[   29.619679] 
[   29.620598]        CPU0
[   29.621064]        ----
[   29.621482]   lock(&(&sighand->siglock)->rlock);
[   29.622311]   <Interrupt>
[   29.622747]     lock(&(&sighand->siglock)->rlock);
[   29.623562] 
[   29.623562]  *** DEADLOCK ***
[   29.623562] 
[   29.624603] 2 locks held by swapper/1/0:
[   29.625274]  #0:  (rcu_read_lock){......}, at: [<ffffffff810e2df2>] rcu_read_lock+0x0/0x68
[   29.626808]  #1:  (rcu_read_lock){......}, at: [<ffffffff810e2df2>] rcu_read_lock+0x0/0x68
[   29.628333] 
[   29.628333] stack backtrace:
[   29.629258] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.0-rc6-00128-g63a745a #1
[   29.630352] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[   29.631563]  0000000000000000 ffff880034803c00 ffffffff8173e2ff ffff8800329d82c0
[   29.632992]  ffff880034803c50 ffffffff81114f72 0000000000000000 0000000000000000
[   29.635104]  0000000000000001 0000000000000000 ffff8800329d8b60 ffffffff81114825
[   29.637195] Call Trace:
[   29.637910]  <IRQ>  [<ffffffff8173e2ff>] dump_stack+0x4b/0x63
[   29.639263]  [<ffffffff81114f72>] print_usage_bug+0x1ba/0x1cf
[   29.640430]  [<ffffffff81114825>] ? check_usage_backwards+0xba/0xba
[   29.641721]  [<ffffffff8111509a>] mark_lock+0x113/0x201
[   29.642945]  [<ffffffff8111598d>] __lock_acquire+0x343/0xdee
[   29.644210]  [<ffffffff810e4d01>] ? __lock_task_sighand+0xb5/0x10a
[   29.645453]  [<ffffffff81115a59>] ? __lock_acquire+0x40f/0xdee
[   29.646649]  [<ffffffff811167ce>] lock_acquire+0x10a/0x196
[   29.647773]  [<ffffffff811167ce>] ? lock_acquire+0x10a/0x196
[   29.648952]  [<ffffffff810e4d01>] ? __lock_task_sighand+0xb5/0x10a
[   29.650180]  [<ffffffff82e307d4>] _raw_spin_lock+0x34/0x6a
[   29.651391]  [<ffffffff810e4d01>] ? __lock_task_sighand+0xb5/0x10a
[   29.652741]  [<ffffffff810e4d01>] __lock_task_sighand+0xb5/0x10a
[   29.654091]  [<ffffffff810e4d88>] do_send_sig_info+0x32/0x72
[   29.655338]  [<ffffffff810e521a>] group_send_sig_info+0x4e/0x56
[   29.656533]  [<ffffffff810e5352>] kill_pid_info+0x44/0x63
[   29.657621]  [<ffffffff8113ad9b>] it_real_fn+0xf4/0xfd
[   29.658726]  [<ffffffff81139d2a>] __hrtimer_run_queues+0x172/0x32c
[   29.660120]  [<ffffffff8113aca7>] ? SyS_getitimer+0x74/0x74
[   29.661422]  [<ffffffff8113a32a>] hrtimer_interrupt+0x7d/0x149
[   29.662736]  [<ffffffff810868a9>] local_apic_timer_interrupt+0x4b/0x4e
[   29.664183]  [<ffffffff82e341e0>] smp_apic_timer_interrupt+0x2e/0x3e
[   29.665581]  [<ffffffff82e3226c>] apic_timer_interrupt+0x8c/0xa0
[   29.666933]  <EOI>  [<ffffffff81092305>] ? native_safe_halt+0x6/0x8
[   29.668441]  [<ffffffff8105f2ee>] default_idle+0x24/0x37
[   29.669674]  [<ffffffff8105f93b>] arch_cpu_idle+0xf/0x11
[   29.670930]  [<ffffffff8110d1c0>] default_idle_call+0x28/0x2f
[   29.672242]  [<ffffffff8110d39b>] cpu_startup_entry+0x17a/0x29a
[   29.673526]  [<ffffffff81085757>] start_secondary+0xe0/0xe3
[   30.393040] trinity-main (852) used greatest stack depth: 12576 bytes left
[   35.497090] random: nonblocking pool is initialized
[   73.263306] init: Failed to create pty - disabling logging for job





Thanks,
Ying Huang