On Thu, Feb 24, 2022, Sean Christopherson wrote:
> Reacquire kvm->srcu in vcpu_run() before returning to the caller if srcu
> was dropped to handle pending work. If the task receives a signal, KVM
> will exit without reacquiring kvm->srcu, resulting in an unbalanced
> unlock kvm_arch_vcpu_ioctl_run(), and eventually hung tasks.
>
> =====================================
> WARNING: bad unlock balance detected!
> 5.17.0-rc3+ #749 Not tainted
> -------------------------------------
> CPU 0/KVM/1803 is trying to release lock (&kvm->srcu) at:
> [<ffffffff81042a19>] kvm_arch_vcpu_ioctl_run+0x669/0x1f60
> but there are no more locks to release!
>
> other info that might help us debug this:
> 1 lock held by CPU 0/KVM/1803:
> #0: ffff88810489c0b0 (&vcpu->mutex){....}-{3:3}, at: kvm_vcpu_ioctl+0x77/0x690
>
> stack backtrace:
> CPU: 7 PID: 1803 Comm: CPU 0/KVM Not tainted 5.17.0-rc3+ #749
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> Call Trace:
> <TASK>
> dump_stack_lvl+0x34/0x44
> lock_release+0x1b4/0x240
> kvm_arch_vcpu_ioctl_run+0x680/0x1f60
> kvm_vcpu_ioctl+0x279/0x690
> __x64_sys_ioctl+0x83/0xb0
> do_syscall_64+0x3b/0xc0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> </TASK>
> INFO: task stable:2347 blocked for more than 120 seconds.
> Not tainted 5.17.0-rc3+ #749
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:stable state:D stack: 0 pid: 2347 ppid: 2340 flags:0x00000000
> Call Trace:
> <TASK>
> __schedule+0x328/0xa00
> schedule+0x44/0xb0
> schedule_timeout+0x26f/0x300
> wait_for_completion+0x84/0xe0
> __synchronize_srcu.part.0+0x7a/0xa0
> kvm_swap_active_memslots+0x141/0x180
> kvm_set_memslot+0x2f9/0x470
> kvm_set_memory_region+0x29/0x40
> kvm_vm_ioctl+0x2c3/0xd70
> __x64_sys_ioctl+0x83/0xb0
> do_syscall_64+0x3b/0xc0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> </TASK>
> INFO: lockdep is turned off.
Ugh, the task hung is actually a different mess introduced by the same patch.
I suspect I'm hitting the one Like reported.
I'll get a fix posted shortly...
