Date:   Wed, 8 Jan 2020 07:14:51 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+607007c8d18f132ad6f4@...kaller.appspotmail.com>,
        Daniel Axtens <dja@...ens.net>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Drewry <wad@...omium.org>
Subject: Re: INFO: rcu detected stall in sys_sendto (2)

On Wed, Jan 8, 2020 at 7:05 AM syzbot
<syzbot+607007c8d18f132ad6f4@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    ae608821 Merge tag 'trace-v5.5-rc5' of git://git.kernel.or..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1581deb9e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=db5ff86cbb23b415
> dashboard link: https://syzkaller.appspot.com/bug?extid=607007c8d18f132ad6f4
> 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+607007c8d18f132ad6f4@...kaller.appspotmail.com

This is:

#syz dup: INFO: rcu detected stall in sys_kill

For details see:
https://groups.google.com/g/syzkaller-bugs/c/Vv3ARjLvagc/m/nZAubeo9AQAJ
https://syzkaller.appspot.com/bug?extid=de8d933e7d153aa0c1bb

I temporarily re-enabled smack instance and it produces another 50
stalls all over the kernel. So smack + KASAN + VMAP stack combination
is sitll problematic.


> rcu: INFO: rcu_preempt self-detected stall on CPU
> rcu:    0-...!: (10499 ticks this GP) idle=2de/1/0x4000000000000002
> softirq=13619/13619 fqs=0
>         (t=10500 jiffies g=6765 q=74)
> rcu: rcu_preempt kthread starved for 10500 jiffies! g6765 f0x0
> RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
> rcu: RCU grace-period kthread stack dump:
> rcu_preempt     R  running task    28984    10      2 0x80004000
> Call Trace:
>   context_switch kernel/sched/core.c:3385 [inline]
>   __schedule+0x9a0/0xcc0 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
> NMI backtrace for cpu 0
> CPU: 0 PID: 8526 Comm: syz-executor.4 Not tainted 5.5.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>   <IRQ>
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x1fb/0x318 lib/dump_stack.c:118
>   nmi_cpu_backtrace+0xaf/0x1a0 lib/nmi_backtrace.c:101
>   nmi_trigger_cpumask_backtrace+0x174/0x290 lib/nmi_backtrace.c:62
>   arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
>   trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
>   rcu_dump_cpu_stacks+0x15a/0x220 kernel/rcu/tree_stall.h:254
>   print_cpu_stall kernel/rcu/tree_stall.h:455 [inline]
>   check_cpu_stall kernel/rcu/tree_stall.h:529 [inline]
>   rcu_pending kernel/rcu/tree.c:2827 [inline]
>   rcu_sched_clock_irq+0xe25/0x1ad0 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:1517 [inline]
>   __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1579
>   hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1641
>   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:memcg_kmem_uncharge include/linux/memcontrol.h:1402 [inline]
> RIP: 0010:free_thread_stack+0x124/0x590 kernel/fork.c:284
> Code: ff 48 c1 e8 06 48 83 e0 c0 48 bf 00 00 00 00 00 ea ff ff 48 01 c7 be
> 03 00 00 00 e8 86 91 61 00 e9 5d 04 00 00 e8 3c 2c 2e 00 <48> 89 df 31 f6
> e8 02 8d 6f 00 43 80 3c 2e 00 74 08 4c 89 e7 e8 73
> RSP: 0018:ffffc90002676da8 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
> RAX: ffffffff81489244 RBX: ffffea00026354c0 RCX: ffff888094f7c080
> RDX: 0000000000000000 RSI: 00000000fffffffc RDI: ffffea00026354c0
> RBP: ffffc90002676de0 R08: 000000000003a728 R09: ffffed10123e36a9
> R10: ffffed10123e36a9 R11: 0000000000000000 R12: ffff88808e5db7a0
> R13: dffffc0000000000 R14: 1ffff11011cbb6f4 R15: ffff888091f1b538
>   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
>   vprintk_emit+0x36d/0x3a0 kernel/printk/printk.c:1997
>   dev_vprintk_emit+0x495/0x513 drivers/base/core.c:3603
>   dev_printk_emit+0x6a/0x8c drivers/base/core.c:3614
>   __netdev_printk+0x301/0x3e9 net/core/dev.c:10217
>   netdev_info+0xb9/0xe4 net/core/dev.c:10272
>   dev_change_name+0x8a5/0x9b0 net/core/dev.c:1242
>   do_setlink+0x8bf/0x3960 net/core/rtnetlink.c:2571
>   __rtnl_newlink net/core/rtnetlink.c:3238 [inline]
>   rtnl_newlink+0x14dd/0x1bd0 net/core/rtnetlink.c:3363
>   rtnetlink_rcv_msg+0x889/0xd40 net/core/rtnetlink.c:5424
>   netlink_rcv_skb+0x19e/0x3d0 net/netlink/af_netlink.c:2477
>   rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5442
>   netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
>   netlink_unicast+0x767/0x920 net/netlink/af_netlink.c:1328
>   netlink_sendmsg+0xa31/0xd50 net/netlink/af_netlink.c:1917
>   sock_sendmsg_nosec net/socket.c:639 [inline]
>   sock_sendmsg net/socket.c:659 [inline]
>   __sys_sendto+0x442/0x5e0 net/socket.c:1985
>   __do_sys_sendto net/socket.c:1997 [inline]
>   __se_sys_sendto net/socket.c:1993 [inline]
>   __x64_sys_sendto+0xe5/0x100 net/socket.c:1993
>   do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x414c43
> Code: ff 0f 83 b0 19 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00
> 83 3d 2d 38 66 00 00 75 17 49 89 ca b8 2c 00 00 00 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 81 19 00 00 c3 48 83 ec 08 e8 87 fa ff ff
> RSP: 002b:00007ffd9886f818 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: 0000000000a71da0 RCX: 0000000000414c43
> RDX: 0000000000000030 RSI: 0000000000a71df0 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 00007ffd9886f820 R09: 000000000000000c
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000a71df0 R15: 0000000000000005
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
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