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Date:   Tue, 5 May 2020 13:35:34 -0700
From:   Khazhismel Kumykov <khazhy@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Roman Penyaev <rpenyaev@...e.de>, Jason Baron <jbaron@...mai.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/1] epoll: call final ep_events_available() check under
 the lock

On Tue, May 5, 2020 at 1:04 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 05 May 2020 10:42:05 +0200 Roman Penyaev <rpenyaev@...e.de> wrote:
>
> > May I ask you to remove "epoll: ensure ep_poll() doesn't miss wakeup
> > events" from your -mm queue? Jason lately found out that the patch
> > does not fully solve the problem and this one patch is a second
> > attempt to do things correctly in a different way (namely to do
> > the final check under the lock). Previous changes are not needed.
>
> Where do we stand with Khazhismel's "eventpoll: fix missing wakeup for
> ovflist in ep_poll_callback"?
>
> http://lkml.kernel.org/r/20200424190039.192373-1-khazhy@google.com
>

My understanding is - we need the ep_poll_callback fix on a logical
level (ovfllist was never triggering wakeup), and the two follow-ups
close races - in both how we add/remove from the wait queue, and how
we observe the ready list, which are needed if we only wake when we
add events, where before we were also waking when we were splicing
ovflist events when reading the ready list. As well, the first two
together are needed for epoll60 to pass in my testing.

Khazhy

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