linux-kernel - Re: epoll with ONESHOT possibly fails to deliver events

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Message-ID: <20121220213210.GA22655@dcvr.yhbt.net>
Date:	Thu, 20 Dec 2012 21:32:10 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Andreas Voellmy <andreas.voellmy@...e.edu>
Cc:	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"junchang.wang@...e.edu Wang" <junchang.wang@...e.edu>
Subject: Re: epoll with ONESHOT possibly fails to deliver events

Andreas Voellmy <andreas.voellmy@...e.edu> wrote:
> I wrote a C program that behaves similar to my original program and
> triggers the bug. The bug only arises when I use enough cores and
> threads (about 16). The program is here:
> https://github.com/AndreasVoellmy/epollbug/blob/master/epollbug.c

I finally took a closer look at your code.   I think your socketCheck()
thread is draining socket and causing the normal threads to miss
events.

Use the FIONREAD ioctl() instead to get unread bytes instead of recv().
If you want to recv() without draining the socket, you can also use
the MSG_PEEK flag.
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