Re: WARNING: suspicious RCU usage in idtentry_exit

[Thomas Gleixner <tglx@linutronix.de>]

syzbot <syzbot+3ae5eaae0809ee311e75@syzkaller.appspotmail.com> writes:

+ Paolo, Paul

> syzbot found the following crash on:
>
> HEAD commit:    7b4cb0a4 Add linux-next specific files for 20200525
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13356016100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10
> dashboard link: https://syzkaller.appspot.com/bug?extid=3ae5eaae0809ee311e75
> 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+3ae5eaae0809ee311e75@syzkaller.appspotmail.com
>
> =============================
> WARNING: suspicious RCU usage
> 5.7.0-rc7-next-20200525-syzkaller #0 Not tainted
> -----------------------------
> kernel/rcu/tree.c:715 RCU dynticks_nesting counter underflow/zero!!
>
> other info that might help us debug this:
>
>
> RCU used illegally from idle CPU!
> rcu_scheduler_active = 2, debug_locks = 1
> RCU used illegally from extended quiescent state!
> no locks held by syz-executor.5/24641.
>
> stack backtrace:
> CPU: 1 PID: 24641 Comm: syz-executor.5 Not tainted 5.7.0-rc7-next-20200525-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  rcu_irq_exit_preempt+0x1fa/0x250 kernel/rcu/tree.c:715
>  idtentry_exit+0x9e/0xc0 arch/x86/entry/common.c:583
>  exc_general_protection+0x23d/0x520 arch/x86/kernel/traps.c:506
>  asm_exc_general_protection+0x1e/0x30 arch/x86/include/asm/idtentry.h:353
> RIP: 0010:kvm_fastop_exception+0xb68/0xfe8
> Code: f2 ff ff ff 48 31 db e9 fb c9 2a f9 b8 f2 ff ff ff 48 31 f6 e9 ff c9 2a f9 31 c0 e9 ec 2c 2b f9 b8 fb ff ff ff e9 13 a9 31 f9 <b9> fb ff ff ff 31 c0 31 d2 e9 33 a9 31 f9 31 db e9 2a 0b 42 f9 31
> RSP: 0018:ffffc90004a87a30 EFLAGS: 00010212
> RAX: 0000000000040000 RBX: ffff88809cca4080 RCX: 0000000000000122
> RDX: 00000000000063ff RSI: ffffc90004a87a98 RDI: 0000000000000122
> RBP: 0000000000000122 R08: ffff888058486480 R09: fffffbfff131f481
> R10: ffffffff898fa403 R11: fffffbfff131f480 R12: 0000000000000122
> R13: 0000000000000078 R14: 0000000000000006 R15: ffffffff88244b5c
>  paravirt_read_msr_safe arch/x86/include/asm/paravirt.h:178 [inline]
>  vmx_create_vcpu+0x184/0x2b40 arch/x86/kvm/vmx/vmx.c:6827
>  kvm_arch_vcpu_create+0x6a8/0xb30 arch/x86/kvm/x86.c:9427
>  kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:3043 [inline]
>  kvm_vm_ioctl+0x15b7/0x2460 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3603
>  vfs_ioctl fs/ioctl.c:48 [inline]
>  ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
>  __do_sys_ioctl fs/ioctl.c:762 [inline]
>  __se_sys_ioctl fs/ioctl.c:760 [inline]
>  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
>  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:353
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45ca29
> Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f2c93b11c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000004e73c0 RCX: 000000000045ca29
> RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000004
> RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 0000000000000396 R14: 00000000004c62c6 R15: 00007f2c93b126d4

Weird. I have no idea how that thing is an EQS here.

Thanks,

        tglx