Re: WARNING in percpu_ref_switch_to_atomic_rcu

[Dmitry Vyukov]

On Tue, Mar 31, 2020 at 3:28 PM syzbot
<syzbot+0076781e1606f479425e@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    770fbb32 Add linux-next specific files for 20200228
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1414f7ade00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=576314276bce4ad5
> dashboard link: https://syzkaller.appspot.com/bug?extid=0076781e1606f479425e
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> 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+0076781e1606f479425e@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> percpu ref (io_file_data_ref_zero) <= 0 (0) after switching to atomic

Looking at this io_file_data_ref_zero, this seems to be io_uring
related. +io_uring maintainers

> WARNING: CPU: 0 PID: 0 at lib/percpu-refcount.c:160 percpu_ref_switch_to_atomic_rcu+0x436/0x540 lib/percpu-refcount.c:160
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.0-rc3-next-20200228-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+0x188/0x20d lib/dump_stack.c:118
>  panic+0x2e3/0x75c kernel/panic.c:221
>  __warn.cold+0x2f/0x35 kernel/panic.c:582
>  report_bug+0x27b/0x2f0 lib/bug.c:195
>  fixup_bug arch/x86/kernel/traps.c:175 [inline]
>  fixup_bug arch/x86/kernel/traps.c:170 [inline]
>  do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267
>  do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
> RIP: 0010:percpu_ref_switch_to_atomic_rcu+0x436/0x540 lib/percpu-refcount.c:160
> Code: 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 f7 00 00 00 49 8b 75 e8 4c 89 e2 48 c7 c7 e0 d1 71 88 e8 02 36 b5 fd <0f> 0b e9 2b fd ff ff e8 7e 6a e3 fd be 08 00 00 00 48 89 ef e8 51
> RSP: 0018:ffffc90000007df0 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000100 RSI: ffffffff815c4e91 RDI: fffff52000000fb0
> RBP: ffff88808c4b2810 R08: ffffffff8987a480 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff88808c4b2838 R14: 0000000000000002 R15: 0000000000000007
>  rcu_do_batch kernel/rcu/tree.c:2218 [inline]
>  rcu_core+0x59f/0x1370 kernel/rcu/tree.c:2445
>  __do_softirq+0x26c/0x99d kernel/softirq.c:292
>  invoke_softirq kernel/softirq.c:373 [inline]
>  irq_exit+0x192/0x1d0 kernel/softirq.c:413
>  exiting_irq arch/x86/include/asm/apic.h:546 [inline]
>  smp_apic_timer_interrupt+0x19e/0x600 arch/x86/kernel/apic/apic.c:1146
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
>  </IRQ>
> RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
> Code: cc cc cc cc cc cc cc cc cc cc cc cc e9 07 00 00 00 0f 00 2d e4 35 65 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d d4 35 65 00 fb f4 <c3> cc 41 56 41 55 41 54 55 53 e8 f3 25 9d f9 e8 8e f7 cf fb 0f 1f
> RSP: 0018:ffffffff89807d98 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
> RAX: 1ffffffff132790a RBX: ffffffff8987a480 RCX: 0000000000000000
> RDX: dffffc0000000000 RSI: 0000000000000006 RDI: ffffffff8987ad1c
> RBP: dffffc0000000000 R08: ffffffff8987a480 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff130f490
> R13: 0000000000000000 R14: ffffffff8a862140 R15: 0000000000000000
>  arch_safe_halt arch/x86/include/asm/paravirt.h:144 [inline]
>  default_idle+0x49/0x350 arch/x86/kernel/process.c:698
>  cpuidle_idle_call kernel/sched/idle.c:154 [inline]
>  do_idle+0x393/0x690 kernel/sched/idle.c:269
>  cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:361
>  start_kernel+0x867/0x8a1 init/main.c:1001
>  secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
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