Re: [syzbot] possible deadlock in scheduler_tick

[Paolo Bonzini]

On 24/03/21 12:34, Wanpeng Li wrote:
> Cc David Woodhouse,
> On Wed, 24 Mar 2021 at 18:11, syzbot
> <syzbot+b282b65c2c68492df769@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    1c273e10 Merge tag 'zonefs-5.12-rc4' of git://git.kernel.o..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13c0414ed00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=6abda3336c698a07
> > dashboard link: https://syzkaller.appspot.com/bug?extid=b282b65c2c68492df769
> > userspace arch: i386
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d86ad6d00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17b8497cd00000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+b282b65c2c68492df769@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > =====================================================
> > WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
> > 5.12.0-rc3-syzkaller #0 Not tainted
> > -----------------------------------------------------
> > syz-executor030/8435 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> > ffffc90001a2a230 (&kvm->arch.pvclock_gtod_sync_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
> > ffffc90001a2a230 (&kvm->arch.pvclock_gtod_sync_lock){+.+.}-{2:2}, at: get_kvmclock_ns+0x25/0x390 arch/x86/kvm/x86.c:2587
> >
> > and this task is already holding:
> > ffff8880b9d35198 (&rq->lock){-.-.}-{2:2}, at: rq_lock kernel/sched/sched.h:1321 [inline]
> > ffff8880b9d35198 (&rq->lock){-.-.}-{2:2}, at: __schedule+0x21c/0x21b0 kernel/sched/core.c:4990
> > which would create a new lock dependency:
> >   (&rq->lock){-.-.}-{2:2} -> (&kvm->arch.pvclock_gtod_sync_lock){+.+.}-{2:2}
> >
> > but this new dependency connects a HARDIRQ-irq-safe lock:
> >   (&rq->lock){-.-.}-{2:2}
> >
> > ... which became HARDIRQ-irq-safe at:
> >    lock_acquire kernel/locking/lockdep.c:5510 [inline]
> >    lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475
> >    __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >    _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> >    rq_lock kernel/sched/sched.h:1321 [inline]
> >    scheduler_tick+0xa4/0x4b0 kernel/sched/core.c:4538
> >    update_process_times+0x191/0x200 kernel/time/timer.c:1801
> >    tick_periodic+0x79/0x230 kernel/time/tick-common.c:100
> >    tick_handle_periodic+0x41/0x120 kernel/time/tick-common.c:112
> >    timer_interrupt+0x3f/0x60 arch/x86/kernel/time.c:57
> >    __handle_irq_event_percpu+0x303/0x8f0 kernel/irq/handle.c:156
> >    handle_irq_event_percpu kernel/irq/handle.c:196 [inline]
> >    handle_irq_event+0x102/0x290 kernel/irq/handle.c:213
> >    handle_level_irq+0x256/0x6e0 kernel/irq/chip.c:650
> >    generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
> >    handle_irq arch/x86/kernel/irq.c:231 [inline]
> >    __common_interrupt+0x9e/0x200 arch/x86/kernel/irq.c:250
> >    common_interrupt+0x9f/0xd0 arch/x86/kernel/irq.c:240
> >    asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:623
> >    __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
> >    _raw_spin_unlock_irqrestore+0x38/0x70 kernel/locking/spinlock.c:191
> >    __setup_irq+0xc72/0x1ce0 kernel/irq/manage.c:1737
> >    request_threaded_irq+0x28a/0x3b0 kernel/irq/manage.c:2127
> >    request_irq include/linux/interrupt.h:160 [inline]
> >    setup_default_timer_irq arch/x86/kernel/time.c:70 [inline]
> >    hpet_time_init+0x28/0x42 arch/x86/kernel/time.c:82
> >    x86_late_time_init+0x58/0x94 arch/x86/kernel/time.c:94
> >    start_kernel+0x3ee/0x496 init/main.c:1028
> >    secondary_startup_64_no_verify+0xb0/0xbb
> >
> > to a HARDIRQ-irq-unsafe lock:
> >   (&kvm->arch.pvclock_gtod_sync_lock){+.+.}-{2:2}
> >
> > ... which became HARDIRQ-irq-unsafe at:
> > ...
> >    lock_acquire kernel/locking/lockdep.c:5510 [inline]
> >    lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475
> >    __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >    _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> >    spin_lock include/linux/spinlock.h:354 [inline]
> >    kvm_synchronize_tsc+0x459/0x1230 arch/x86/kvm/x86.c:2332
> >    kvm_arch_vcpu_postcreate+0x73/0x180 arch/x86/kvm/x86.c:10183
> >    kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:3239 [inline]
> >    kvm_vm_ioctl+0x1b2d/0x2800 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3839
> >    kvm_vm_compat_ioctl+0x125/0x230 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4052
> >    __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
> >    do_syscall_32_irqs_on arch/x86/entry/common.c:77 [inline]
> >    __do_fast_syscall_32+0x56/0x90 arch/x86/entry/common.c:140
> >    do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:165
> >    entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
> >
> > other info that might help us debug this:
> >
> >   Possible interrupt unsafe locking scenario:
> >
> >         CPU0                    CPU1
> >         ----                    ----
> >    lock(&kvm->arch.pvclock_gtod_sync_lock);
> >                                 local_irq_disable();
> >                                 lock(&rq->lock);
> >                                 lock(&kvm->arch.pvclock_gtod_sync_lock);
> >    <Interrupt>
> >      lock(&rq->lock);
>
> The offender is get_kvmclock_ns() which is called in the context
> switch process. The bad commit is 30b5c851af7991ad0 ("KVM: x86/xen:
> Add support for vCPU runstate information").

I'll send a patch, thanks.

Paolo