Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()

[Paolo Bonzini]

On 15/07/21 10:44, He Zhe wrote:
> It was to increase the recursion depth to 2 so that vhost_worker and
> kvm_vcpu_ioctl syscall could work in parallel

The count is per-CPU, so parallel operations cannot cause it to become 
2.  Your patch might fix calls from ioeventfd to vhost_worker to another 
eventfd, but not *parallel* operation of KVM and vhost (except on 
PREEMPT_RT).

You should identify the exact callstack that caused the warning for 
vDUSE, and document that one in the commit message, so that reviewers 
can understand the issue.

Paolo