linux-kernel - Re: disappearing listen()ed SO_REUSEPORT sockets across fork() when using epoll

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Date:	Mon, 25 Nov 2013 11:53:24 -0800
From:	Shawn Landden <shawnlandden@...il.com>
To:	Jason Baron <jbaron@...mai.com>
Cc:	linux-fsdevel@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: disappearing listen()ed SO_REUSEPORT sockets across fork() when
 using epoll

On Mon, Nov 25, 2013 at 10:05 AM, Jason Baron <jbaron@...mai.com> wrote:
> On 11/22/2013 12:53 PM, Shawn Landden wrote:
>> Hello, when running the attached program on 3.12 child processes
>> are missing a socket fd opened, set with SO_REUSEPORT, listen()ed to,
>> and added to epoll_ctl().
>>
>> This is the output I get when pointing "wget http://localhost:5555/"
>> at the attached program:
>>
>> main PID 31591
>> PID 31634 started
>> PID 31634 accept()ed connection
>> PID 31635 started
>> PID 31636 started
>> PID 31635 accept() failed: Bad file descriptor
>> PID 31636 accept() failed: Bad file descriptor
>> PID 31634 accept()ed connection
>> PID 31634 accept()ed connection
>> PID 31634 accept()ed connection
>> PID 31634 accept()ed connection
>>
>>
>> While I would expect something like:
>>
>> main PID 31591
>> PID 31634 started
>> PID 31634 accept()ed connection
>> PID 31635 started
>> PID 31636 started
>> PID 31635 accept()ed connection
>> PID 31636 accept()ed connection
>>
>> -more new processes, but inversely proportional to number of listening processes
>> -accept() always returns successfully
>>
>>
>
> The 'close(sockfd);' looks to be racing with the accept() calls. Removing seems
> to get the result you are looking for.
Interesting. That works, but it shouldn't. The close() is operating in
the parent, so it shouldn't affect the child,
there is a leak here of process separation.

New version with pid set to volatile, and making sure that we are in the parent.
>
> Thanks,
>
> -Jason
>



-- 

---
Shawn Landden
+1 360 389 3001 (SMS preferred)

View attachment "epoll_test.c" of type "text/x-csrc" (2538 bytes)