netdev - Re: [PATCH net-next 3/7] net: rxrpc: change call to sock_recv_ts_and_drops() on rxrpc recvmsg to sock_recv

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Message-ID: <CAHsH6Gstyh+8TRqONtfST9V6-_=LNSvQekfGtJFmPWLZ9onZPw@mail.gmail.com>
Date:	Thu, 26 Feb 2015 16:55:58 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/7] net: rxrpc: change call to
 sock_recv_ts_and_drops() on rxrpc recvmsg to sock_recv_timestamp()

On Thu, Feb 26, 2015 at 4:31 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2015-02-26 at 09:30 +0200, Eyal Birger wrote:
>
>> Maybe I didn't understand your comment. Note this patch does not fix
>> SO_RXQ_OVFL on rxrpc sockets.
>>
>> I essentially reverted 3b885787ea4112 for these sockets.
>>
>> It may be possible to compact rxrpc skb->cb[] usage by tricking the size
>> of the resend_at variable as you suggested.
>>
>> However, since SO_RXQ_OVFL never really worked on these sockets,
>> I limited the patch series scope to moving skb->dropcount; This patch only
>> signals that rxrpc can't support this feature unless some space is freed in its
>> skb->cb[] use.
>> --
>
> My point is : If you stick this patch early in the serie, then skb->mark
> will be overwritten by sock_recv_timestamp() (to store skb->dropcount)
> and rxrpc breaks as it actively relies on skb->mark (apparently)
>

skb->dropcount is stored prior to enqueue in sock_queue_rcv_skb().
This function is not called in rxrpc.

sock_recv_timestamp() is called from the recvmsg code, and does not alter
skb->dropcount.

What am I missing?

> We dont care if SO_RXQ_OVFL is broken for rxprpc : Nobody noticed yet.
>

This was my point in this patch - to make it explicit. When rxrpc called
sock_recv_ts_and_drops() it allegedly supported receiving drops, when
dropcount was never set.

> But breaking rxrpc skb->mark early in the serie does not help bisection
> if needed later.
>
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