netdev - Re: [PATCH net v3 2/3] Treewide: Stop corrupting socket's task

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Date:   Thu, 15 Dec 2022 14:36:52 +0000
From:   David Howells <dhowells@...hat.com>
To:     Guillaume Nault <gnault@...hat.com>
cc:     dhowells@...hat.com, Benjamin Coddington <bcodding@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>, Jens Axboe <axboe@...nel.dk>,
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        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Lee Duncan <lduncan@...e.com>, Chris Leech <cleech@...hat.com>,
        Mike Christie <michael.christie@...cle.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
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        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net v3 2/3] Treewide: Stop corrupting socket's task_frag


Guillaume Nault <gnault@...hat.com> wrote:

> Maybe setting sk_use_task_frag in fs/afs/rxrpc.c was overzealous but
> I'm not familiar enough with the AF_RXRPC family to tell. If AF_RXRPC
> sockets can't call sk_page_frag() and have no reason to do so in the
> future, then it should be safe to drop this chunk.

As of this merge window, AF_RXRPC doesn't actually allocate sk_buffs apart
from when it calls skb_unshare().  It does steal the incoming sk_buffs from
the UDP socket it uses as a transport, but they're allocated in the IP/IP6
stack somewhere.

The UDP transport socket, on the other hand, will allocate sk_buffs for
transmission, but rxrpc sends an entire UDP packet at a time, each with a
single sendmsg call.

Further, this mostly now moved such that the UDP sendmsg calls are performed
inside an I/O thread.  The application thread does not interact directly with
the UDP transport socket.

David