Re: INFO: rcu detected stall in seq_read (2)

[Eric Dumazet]

On 7/22/20 11:02 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4fa640dc Merge tag 'vfio-v5.8-rc7' of git://github.com/awi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=145cac30900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f87a5e4232fdb267
> dashboard link: https://syzkaller.appspot.com/bug?extid=c28b5fee66fd3b7f766e
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17e23ac8900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1198c440900000
> 
> The issue was bisected to:
> 
> commit 53e233ea2fa9fa7e2405e95070981f327d90e519
> Author: Vasundhara Volam <vasundhara-v.volam@xxxxxxxxxxxx>
> Date:   Thu Oct 4 05:43:52 2018 +0000
> 
>     devlink: Add Documentation/networking/devlink-params-bnxt.txt

Probably bogus bisection.

This rather looks like a bug in taprio packet scheduler.



> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15e22b94900000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=17e22b94900000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13e22b94900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c28b5fee66fd3b7f766e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 53e233ea2fa9 ("devlink: Add Documentation/networking/devlink-params-bnxt.txt")
> 
> hrtimer: interrupt took 6305559 ns
> rcu: INFO: rcu_preempt self-detected stall on CPU
> rcu: 	1-...!: (1 GPs behind) idle=91e/1/0x4000000000000000 softirq=10105/10107 fqs=1 
> 	(t=18319 jiffies g=8905 q=457)
> NMI backtrace for cpu 1
> CPU: 1 PID: 4008 Comm: systemd-journal Not tainted 5.8.0-rc6-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+0x18f/0x20d lib/dump_stack.c:118
>  nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
>  nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
>  trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
>  rcu_dump_cpu_stacks+0x194/0x1cf kernel/rcu/tree_stall.h:320
>  print_cpu_stall kernel/rcu/tree_stall.h:553 [inline]
>  check_cpu_stall kernel/rcu/tree_stall.h:627 [inline]
>  rcu_pending kernel/rcu/tree.c:3489 [inline]
>  rcu_sched_clock_irq.cold+0x5b3/0xccc kernel/rcu/tree.c:2504
>  update_process_times+0x25/0x60 kernel/time/timer.c:1737
>  tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176
>  tick_sched_timer+0x108/0x290 kernel/time/tick-sched.c:1320
>  __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
>  __hrtimer_run_queues+0x1d5/0xfc0 kernel/time/hrtimer.c:1584
>  hrtimer_interrupt+0x32a/0x930 kernel/time/hrtimer.c:1646
>  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
>  __sysvec_apic_timer_interrupt+0x142/0x5e0 arch/x86/kernel/apic/apic.c:1097
>  asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
>  </IRQ>
>  __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
>  run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
>  sysvec_apic_timer_interrupt+0xe0/0x120 arch/x86/kernel/apic/apic.c:1091
>  asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:585
> RIP: 0010:format_decode+0x0/0xad0 lib/vsprintf.c:2329
> Code: c7 c7 10 05 af 8a be 10 00 00 00 e8 5a c3 46 00 48 c7 c7 20 78 0d 8a e9 6e f2 e2 fd 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 <41> 57 41 56 41 55 41 54 55 48 89 f5 53 48 bb 00 00 00 00 00 fc ff
> RSP: 0018:ffffc90001077a10 EFLAGS: 00000293
> RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff83b0a497
> RDX: ffff888093224040 RSI: ffffc90001077a80 RDI: ffffffff884e6293
> RBP: ffffffff884e6293 R08: 0000000000000001 R09: ffff8880952a63d1
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880952a63d2
> R13: ffffffff884e6293 R14: 0000000000000025 R15: ffffc90001077b30
>  vsnprintf+0x155/0x14f0 lib/vsprintf.c:2572
>  seq_vprintf fs/seq_file.c:379 [inline]
>  seq_printf+0x195/0x240 fs/seq_file.c:394
>  proc_pid_status+0x1c6d/0x24b0 fs/proc/array.c:424
>  proc_single_show+0x116/0x1e0 fs/proc/base.c:766
>  seq_read+0x432/0x1070 fs/seq_file.c:208
>  vfs_read+0x1df/0x520 fs/read_write.c:479
>  ksys_read+0x12d/0x250 fs/read_write.c:607
>  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7f0fc43d9910
> Code: Bad RIP value.
> RSP: 002b:00007ffdcb193978 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 000055b1476b96f0 RCX: 00007f0fc43d9910
> RDX: 0000000000000800 RSI: 000055b1476b8b00 RDI: 0000000000000013
> RBP: 00007f0fc4694440 R08: 00007f0fc4697fc8 R09: 0000000000000410
> R10: 000055b1476b96f0 R11: 0000000000000246 R12: 0000000000000800
> R13: 0000000000000d68 R14: 000055b1476b8b00 R15: 00007f0fc4693900
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
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> 
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
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>