Re: INFO: rcu detected stall in sys_kill

[Dmitry Vyukov]

On Tue, Dec 17, 2019 at 2:39 PM Daniel Axtens <dja@xxxxxxxxxx> wrote:
>
> Daniel Axtens <dja@xxxxxxxxxx> writes:
>
> > Hi Casey,
> >
> >> 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.
> >
> > Yeah, I'm having a look, it's probably related to my kasan-vmalloc
> > stuff. It's currently in a bit of flux as syzkaller finds a bunch of
> > other bugs with it, once that stablises a bit I'll come back to Smack.
>
> I have had a brief and wildly unsuccessful look at this. I'm happy to
> come back to it and go over it with a finer toothed comb, but it will
> almost certainly have to wait until next year.
>
> I don't think it's related to RCU, we also have a plain lockup:
> https://syzkaller.appspot.com/bug?id=be03729d17bb3b2df1754a7486a8f8628f6ff1ec
>
> Dmitry, I've been really struggling to repro this locally, even with
> your config. Is there an easy way to see the kernel command line you
> booted with and anything else that makes this image special? I have zero
> experience with smack so this is a steep learning curve.

I temporarily re-enabled smack instance and it produced another 50
stalls all over the kernel, and now keeps spewing a dozen every hour.

I've mailed 3 new samples, you can see them here:
https://syzkaller.appspot.com/bug?extid=de8d933e7d153aa0c1bb

The config is provided, command line args are here:
https://github.com/google/syzkaller/blob/master/dashboard/config/upstream-smack.cmdline
Some non-default sysctls that syzbot sets are here:
https://github.com/google/syzkaller/blob/master/dashboard/config/upstream.sysctl
Image can be downloaded from here:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#crash-does-not-reproduce
syzbot uses GCE VMs with 2 CPUs and 7.5GB memory, but this does not
look to be virtualization-related (?) so probably should reproduce in
qemu too.



> Regards,
> Daniel
>
> >
> > Regards,
> > Daniel
> >
> >>
> >>>>
> >>>> 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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>
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