Re: Strange issues with epoll since 5.0

[Davidlohr Bueso]

On Wed, 24 Apr 2019, Davidlohr Bueso wrote:

> On Wed, 24 Apr 2019, Eric Wong wrote:
>
> > Omar Kilani <omar.kilani@xxxxxxxxx> wrote:
> > > Hi there,
> > >
> > > I???m still trying to piece together a reproducible test that triggers
> > > this, but I wanted to post in case someone goes ???hmmm... change X
> > > might have done this???.
> >
> > Maybe Davidlohr knows, since he's responsible for most of the
> > epoll changes in 5.0.
>
> Not really, I have not been made aware of any issues until now.
>
> > > Basically, something???s broken (or at least, has changed enough to
> > > cause problems in user space) in epoll since 5.0. It???s still broken in
> > > 5.1-rc5.
> > >
> > > It doesn???t happen 100% of the time. It???s sort of hard to pin down but
> > > I???ve observed the following:
> > >
> > > * nginx not accepting connections under load
> > > * A java app which uses netty / NIO having strange writability
> > > semantics on channels, which confuses netty / java enough to not
> > > properly flush written data on the socket.

Off the top of my head, could the following be responsible?

c5a282e9635 (fs/epoll: reduce the scope of wq lock in epoll_wait())