netdev - Re: [PATCH net-next 2/7] rds: hold a sock ref from rds_message to the rds

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Message-ID: <20180128161832.GB22885@oracle.com>
Date:   Sun, 28 Jan 2018 11:18:32 -0500
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, rds-devel@....oracle.com,
        santosh.shilimkar@...cle.com
Subject: Re: [PATCH net-next 2/7] rds: hold a sock ref from rds_message to
 the rds_sock

On (01/28/18 14:51), Willem de Bruijn wrote:
> > On (01/25/18 15:44), Willem de Bruijn wrote:
     ;
> >> You may alos be able to do the same as tcp zerocopy and
> >> hold an sk reference on the notification skb.
     ;
> I don't quite follow. Every notification skb is created when pages refcount
> is increased. It persists until at least rds_rm_zerocopy_callback, after data
> skb has been freed and pages refcount has been decreased.
> 
> In this callback, skb is consumed if another skb is already queued on
> the error queue, otherwise it is queued itself. It needs to hold a sock ref
> until it can be queued.

maybe I did not follow the original suggestion- were you 
suggesting that I hold a pointer to the sk from e.g., the skb->cb
itself? I dont know that it would make things simpler, 
whereas having the pointer and refcount in the rds_message itself,
and track this independantly of whether/not zcopy was used, seems 
like a more consistent dsta-structure model, so I'd like to leave 
this as is.