netdev - Re: [PATCH] [doc] msg_zerocopy.rst: clarify the TCP shutdown scenario

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Message-ID: <CA+FuTSeqbu=MPdmOVSHBDy39ZxrHZUjgGmP4LhPXjWsfc_Qa+g@mail.gmail.com>
Date:   Fri, 3 Jun 2022 09:30:18 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Frederik Deweerdt <frederik.deweerdt@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] [doc] msg_zerocopy.rst: clarify the TCP shutdown scenario

On Fri, Jun 3, 2022 at 9:18 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Frederik Deweerdt <frederik.deweerdt@...il.com>
> > Sent: 02 June 2022 00:01
> > >
> > > A socket must not be closed until all completion notifications have
> > > been received.
> > >
> > > Calling shutdown is an optional step. It may be sufficient to simply
> > > delay close.
>
> What happens if the process gets killed - eg by SIGSEGV?

The skb frags hold independent references on the pages. Once skbs are
freed on transmit completion or socket purge the pages are released if
there are no other page references.

Otherwise there is nothing zerocopy specific about closing TCP
connections when a process crashes.