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

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Message-Id: <4335C40C-5F4E-484F-8D4B-38D6A244259A@yale.edu>
Date:	Tue, 18 Dec 2012 12:27:10 -0500
From:	Andreas Voellmy <andreas.voellmy@...e.edu>
To:	Eric Wong <normalperson@...t.net>
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

BTW, I simplified the test program a bit: I removed the loop that epoll_waits on the eventfd fd and reads from it (I also removed the epoll instance in that loop).  The bug still occurs with this removed. Now the bug is triggered simply by adding the call to eventfd_write after processing each request. 

I pushed the update to my github project for the test program.

-Andi

On Dec 17, 2012, at 9:35 PM, Andreas Voellmy <andreas.voellmy@...e.edu> wrote:

> 
> On Dec 17, 2012, at 9:07 PM, Eric Wong <normalperson@...t.net> wrote:
> 
>> Andreas Voellmy <andreas.voellmy@...e.edu> wrote:
>>> There were a couple of errors in the code when I posted my last
>>> message. I have fixed those. The epoll bug still occurs. 
>> 
>> Sorry I haven't gotten around to this.
>> 
>> Can you reproduce this with fewer cores? (I only have 4 at most).
> 
> I've been able to reproduce it on as few as 8 cores. I've never seen it occur with fewer than that.
> 
>> Have you tried the latest stable kernel version?
> 
> No, I've only tried 3.4.0.0.
> 
>> 
>> Can you reproduce this over TCP loopback, or only across two machines?
>> If the latter, it could also be a driver or firmware bug...
> 
> Yes, it also occurs when I run the http request generator on the same machine on the loopback interface.
> 
> -Andi

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