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SubjectRe: Strange issues with epoll since 5.0
Omar Kilani <omar.kilani@gmail.com> 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.

> 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.
>
> I went and tested these Linux kernels:
>
> 4.20.17
> 4.19.32
> 4.14.111
>
> And the issue(s) do not show up there.
>
> I’m still actively chasing this up, and will report back — I haven’t
> touched kernel code in 15 years so I’m a little rusty. :)
>
> Regards,
> Omar

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