linux-kernel - Re: Strange issues with epoll since 5.0

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Date:   Wed, 24 Apr 2019 14:52:50 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Eric Wong <e@...24.org>
Cc:     linux-kernel@...r.kernel.org, Omar Kilani <omar.kilani@...il.com>
Subject: Re: Strange issues with epoll since 5.0

On Wed, 24 Apr 2019, Davidlohr Bueso wrote:

>On Wed, 24 Apr 2019, Eric Wong wrote:
>
>>Omar Kilani <omar.kilani@...il.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.
>
>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())