Re: [PATCH v2 2/2] xen/evtchn: rework per event channel lock

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.10.2020 11:27, Juergen Gross wrote:
> Currently the lock for a single event channel needs to be taken with
> interrupts off, which causes deadlocks in some cases.
> 
> Rework the per event channel lock to be non-blocking for the case of
> sending an event and removing the need for disabling interrupts for
> taking the lock.
> 
> The lock is needed for avoiding races between sending an event or
> querying the channel's state against removal of the event channel.
> 
> Use a locking scheme similar to a rwlock, but with some modifications:
> 
> - sending an event or querying the event channel's state uses an
>   operation similar to read_trylock(), in case of not obtaining the
>   lock the sending is omitted or a default state is returned

And how come omitting the send or returning default state is valid?

Jan