netdev - Re: [PATCH v3 net-next 2/7] rds: hold a sock ref from rds_message to the rds

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Message-ID: <a5a6eb8c-a24d-fd05-03ca-acf6d72b8ba1@oracle.com>
Date:   Thu, 15 Feb 2018 11:45:43 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        netdev@...r.kernel.org, willemdebruijn.kernel@...il.com
Cc:     davem@...emloft.net, rds-devel@....oracle.com
Subject: Re: [PATCH v3 net-next 2/7] rds: hold a sock ref from rds_message to
 the rds_sock

On 2/15/2018 10:49 AM, Sowmini Varadhan wrote:
> The existing model holds a reference from the rds_sock to the
> rds_message, but the rds_message does not itself hold a sock_put()
> on the rds_sock. Instead the m_rs field in the rds_message is
> assigned when the message is queued on the sock, and nulled when
> the message is dequeued from the sock.
> 
> We want to be able to notify userspace when the rds_message
> is actually freed (from rds_message_purge(), after the refcounts
> to the rds_message go to 0). At the time that rds_message_purge()
> is called, the message is no longer on the rds_sock retransmit
> queue. Thus the explicit reference for the m_rs is needed to
> send a notification that will signal to userspace that
> it is now safe to free/reuse any pages that may have
> been pinned down for zerocopy.
> 
> This patch manages the m_rs assignment in the rds_message with
> the necessary refcount book-keeping.
> 
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
Acked-by: Santosh Shilimkar <santosh.shilimkar@...cle.com>