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

[Paolo Bonzini]

On 24/07/21 06:33, Hillf Danton wrote:
> 		lock WQ
> 		count += n
> 		no waiter
> 		unlock WQ

Ok, this is a write.

> 				lock WQ
> 				add waiter for EPOLLIN
> 				unlock WQ

This is eventfd_poll().  It hasn't yet returned EPOLLIN.

> 						lock WQ
> 						count = 0
> 						wakeup EPOLLOUT
> 						unlock WQ

This is a read().

> lock WQ
> count += n
> no waiter
> unlock WQ

This is wrong; after "unlock WQ" in CPU3 there *is* a waiter, no one has 
waked it up yet.

Paolo

> ------------------------------- c1 = count