linux-kernel - Re: [REGRESSION] Select hang with zero sized UDP packets

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Message-ID: <1472043735.14381.69.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 24 Aug 2016 06:02:15 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dan Akunis <dan.akunis@...il.com>
Cc:     labbott@...hat.com, David Miller <davem@...emloft.net>,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, samanthakumar@...gle.com, willemb@...gle.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] Select hang with zero sized UDP packets

On Wed, 2016-08-24 at 11:22 +0300, Dan Akunis wrote:
> When select wakes up on a UDP socket, user is expecting to get data. Getting 
> 0 from recvfrom() or whatever read function she uses, is a wrong attitude.
> I agree with David.
> 
> The unit test that expects select to wake up is wrong and should be changed.
> 

Please do not top post on netdev mailing list.

Program is fine and wont be changed to work around a kernel bug.

We definitely can send and receive UDP messages with 0 payload.

So select() should unblock when one such frame is received, otherwise
you could fill up the receive queue with a lot of frames like that and
when SO_RCVBUF limit is reached, block future messages.

UDP is a datagram protocol.

Bug fix is merged :
https://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=e83c6744e81abc93a20d0eb3b7f504a176a6126a