Re: INFO: rcu detected stall in sys_kill

[Casey Schaufler]

On 12/4/2019 5:58 AM, Dmitry Vyukov wrote:
> On Tue, Dec 3, 2019 at 9:38 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> On Tue, Dec 3, 2019 at 9:27 AM syzbot
>> <syzbot+de8d933e7d153aa0c1bb@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    596cf45c Merge branch 'akpm' (patches from Andrew)
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15f11c2ae00000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=9bbcda576154a4b4
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=de8d933e7d153aa0c1bb
>>> compiler:       clang version 9.0.0 (/home/glider/llvm/clang
>>> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
>>>
>>> Unfortunately, I don't have any reproducer for this crash yet.
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+de8d933e7d153aa0c1bb@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Something seriously broken in smack+kasan+vmap stacks, we now have 60
>> rcu stalls all over the place and counting. This is one of the
>> samples. I've duped 2 other samples to this one, you can see them on
>> the dashboard:
>> https://syzkaller.appspot.com/bug?extid=de8d933e7d153aa0c1bb

There haven't been Smack changes recently, so this is
going to have been introduced elsewhere. I'm perfectly
willing to accept that Smack is doing something horribly
wrong WRT rcu, and that it needs repair, but its going to
be tough for me to track down. I hope someone else is looking
into this, as my chances of finding the problem are pretty
slim.

>>
>> I see 2 common this across all stalls:
>> 1. They all happen on the instance that uses smack (which is now
>> effectively dead), see smack instance here:
>> https://syzkaller.appspot.com/upstream
>> 2. They all contain this frame in the stack trace:
>> free_thread_stack+0x168/0x590 kernel/fork.c:280
>> The last commit that touches this file is "fork: support VMAP_STACK
>> with KASAN_VMALLOC".
>> That may be very likely the root cause. +Daniel
> I've stopped smack syzbot instance b/c it produces infinite stream of
> assorted crashes due to this.
> Please ping syzkaller@xxxxxxxxxxxxxxxx when this is fixed, I will
> re-enable the instance.
>
>>> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
>>>         (detected by 1, t=10502 jiffies, g=6629, q=331)
>>> rcu: All QSes seen, last rcu_preempt kthread activity 10503
>>> (4294953794-4294943291), jiffies_till_next_fqs=1, root ->qsmask 0x0
>>> syz-executor.0  R  running task    24648  8293   8292 0x0000400a
>>> Call Trace:
>>>   <IRQ>
>>>   sched_show_task+0x40f/0x560 kernel/sched/core.c:5954
>>>   print_other_cpu_stall kernel/rcu/tree_stall.h:410 [inline]
>>>   check_cpu_stall kernel/rcu/tree_stall.h:538 [inline]
>>>   rcu_pending kernel/rcu/tree.c:2827 [inline]
>>>   rcu_sched_clock_irq+0x1861/0x1ad0 kernel/rcu/tree.c:2271
>>>   update_process_times+0x12d/0x180 kernel/time/timer.c:1726
>>>   tick_sched_handle kernel/time/tick-sched.c:167 [inline]
>>>   tick_sched_timer+0x263/0x420 kernel/time/tick-sched.c:1310
>>>   __run_hrtimer kernel/time/hrtimer.c:1514 [inline]
>>>   __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1576
>>>   hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1638
>>>   local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
>>>   smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1135
>>>   apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
>>>   </IRQ>
>>> RIP: 0010:__read_once_size include/linux/compiler.h:199 [inline]
>>> RIP: 0010:check_kcov_mode kernel/kcov.c:70 [inline]
>>> RIP: 0010:__sanitizer_cov_trace_pc+0x1c/0x50 kernel/kcov.c:102
>>> Code: cc 07 48 89 de e8 64 02 3b 00 5b 5d c3 cc 48 8b 04 24 65 48 8b 0c 25
>>> c0 1d 02 00 65 8b 15 b8 81 8b 7e f7 c2 00 01 1f 00 75 2c <8b> 91 80 13 00
>>> 00 83 fa 02 75 21 48 8b 91 88 13 00 00 48 8b 32 48
>>> RSP: 0018:ffffc900021c7c28 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
>>> RAX: ffffffff81487433 RBX: 0000000000000000 RCX: ffff88809428a100
>>> RDX: 0000000000000001 RSI: 00000000fffffffc RDI: ffffea0002479240
>>> RBP: ffffc900021c7c50 R08: dffffc0000000000 R09: fffffbfff1287025
>>> R10: fffffbfff1287025 R11: 0000000000000000 R12: dffffc0000000000
>>> R13: dffffc0000000000 R14: 00000000fffffffc R15: ffff888091c57428
>>>   free_thread_stack+0x168/0x590 kernel/fork.c:280
>>>   release_task_stack kernel/fork.c:440 [inline]
>>>   put_task_stack+0xa3/0x130 kernel/fork.c:451
>>>   finish_task_switch+0x3f1/0x550 kernel/sched/core.c:3256
>>>   context_switch kernel/sched/core.c:3388 [inline]
>>>   __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
>>>   preempt_schedule_common kernel/sched/core.c:4236 [inline]
>>>   preempt_schedule+0xdb/0x120 kernel/sched/core.c:4261
>>>   ___preempt_schedule+0x16/0x18 arch/x86/entry/thunk_64.S:50
>>>   __raw_read_unlock include/linux/rwlock_api_smp.h:227 [inline]
>>>   _raw_read_unlock+0x3a/0x40 kernel/locking/spinlock.c:255
>>>   kill_something_info kernel/signal.c:1586 [inline]
>>>   __do_sys_kill kernel/signal.c:3640 [inline]
>>>   __se_sys_kill+0x5e9/0x6c0 kernel/signal.c:3634
>>>   __x64_sys_kill+0x5b/0x70 kernel/signal.c:3634
>>>   do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
>>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>> RIP: 0033:0x422a17
>>> Code: 44 00 00 48 c7 c2 d4 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e
>>> 0f 1f 84 00 00 00 00 00 0f 1f 40 00 b8 3e 00 00 00 0f 05 <48> 3d 01 f0 ff
>>> ff 0f 83 dd 32 ff ff c3 66 2e 0f 1f 84 00 00 00 00
>>> RSP: 002b:00007fff38dca538 EFLAGS: 00000293 ORIG_RAX: 000000000000003e
>>> RAX: ffffffffffffffda RBX: 0000000000000064 RCX: 0000000000422a17
>>> RDX: 0000000000000bb8 RSI: 0000000000000009 RDI: 00000000fffffffe
>>> RBP: 0000000000000002 R08: 0000000000000001 R09: 0000000001c62940
>>> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000008
>>> R13: 00007fff38dca570 R14: 000000000000f0b6 R15: 00007fff38dca580
>>> rcu: rcu_preempt kthread starved for 10533 jiffies! g6629 f0x2
>>> RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
>>> rcu: RCU grace-period kthread stack dump:
>>> rcu_preempt     R  running task    29032    10      2 0x80004008
>>> Call Trace:
>>>   context_switch kernel/sched/core.c:3388 [inline]
>>>   __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
>>>   schedule+0x181/0x210 kernel/sched/core.c:4155
>>>   schedule_timeout+0x14f/0x240 kernel/time/timer.c:1895
>>>   rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
>>>   rcu_gp_kthread+0xed8/0x1770 kernel/rcu/tree.c:1821
>>>   kthread+0x332/0x350 kernel/kthread.c:255
>>>   ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
>>>
>>>
>>> ---
>>> This bug is generated by a bot. It may contain errors.
>>> See https://goo.gl/tpsmEJ for more information about syzbot.
>>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>>>
>>> syzbot will keep track of this bug report. See:
>>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>>>
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