netdev - Re: [PATCH net-next 1/2] net: SOCKWQ_ASYNC

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Message-ID: <1462222558.5535.279.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Mon, 02 May 2016 13:55:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	jiri@...nulli.us, edumazet@...gle.com, netdev@...r.kernel.org,
	eladr@...lanox.com, idosch@...lanox.com
Subject: Re: [PATCH net-next 1/2] net: SOCKWQ_ASYNC_NOSPACE optimizations

On Mon, 2016-05-02 at 16:31 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Mon, 02 May 2016 13:23:27 -0700
> 
> > It looks like net/sunrpc/xprtsock.c should set SOCK_FASYNC
> > even if it is not actually using fasync_list
> > 
> > Could you try this quick hack to check if this is the right way ?
> 
> Indeed, it tests the ASYNC bit without enabling FASYNC.
> 
> There are three other places that do this: macvtap, tun, dlm lowcomms.

Yes, although macvtap and tun have a private usage of this bit.

When the flag was moved (commit ceb5d58b217098a657f3850b7a2640f995032e62
"net: fix sock_wake_async() rcu protection"), I did not change the code
in these drivers. And apparently nobody complained (linux-4.4)

drivers/net/macvtap.c:501:          !test_and_clear_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags))
drivers/net/macvtap.c:588:          (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &q->sock.flags) &&
drivers/net/tun.c:1111:     (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
drivers/net/tun.c:1576: if (!test_and_clear_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags))

fs/dlm/lowcomms.c probably needs a fix.