linux-kernel - Re: epoll_wait misses edge-triggered eventfd events: bug in Linux 5.3 and 5.4

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Date:   Tue, 04 Feb 2020 11:35:16 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Max Neunhöffer <max@...ngodb.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Christopher Kohlhoff <chris.kohlhoff@...arpool.io>,
        lars@...ngodb.com
Subject: Re: epoll_wait misses edge-triggered eventfd events: bug in Linux 5.3
 and 5.4

On 2020-02-03 22:03, Max Neunhöffer wrote:
> Hi Roman,
> 
> Thanks for your quick response. This sounds fantastic!
> 
> The epollbug.c program was originally written by my colleague Lars
> Maier and then modified by me and subsequently by Chris Kohlhoff. Note
> that the bugzilla bug report contains altogether three variants which
> test epoll_wait/epoll_ctl in three different ways. It might be
> sensible to take all three variants for the test suite.

I checked 3 variants, they do same things: epoll_ctl() races against
epoll_wait(), and this is exactly the bug reproduction, regardless
actual read() from a file descriptor or EPOLLET flag set.

> I cannot imagine that any of the three authors would object to this, I
> definitely do not, the other two are on Cc in this email and can speak
> for themselves.

I adapted the logic from epollbug.c and included it into 
epoll_wakeup_test.c
test suite, you should have received the email: "[PATCH 3/3] kselftest:
introduce new epoll test case".  Please, take a look or ask your 
colleague
to take a look. If no objections - then fine, leave as is.

Thanks.

--
Roman