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

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Message-ID: <20221215153753.GA7408@pc-4.home>
Date:   Thu, 15 Dec 2022 16:37:53 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     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>,
        Josef Bacik <josef@...icpanda.com>,
        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>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Steve French <sfrench@...ba.org>,
        Christine Caulfield <ccaulfie@...hat.com>,
        David Teigland <teigland@...hat.com>,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
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        Latchesar Ionkov <lucho@...kov.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
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        Xiubo Li <xiubli@...hat.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jeff Layton <jlayton@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        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

On Thu, Dec 15, 2022 at 02:36:52PM +0000, David Howells wrote:
> 
> 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

Thanks for the explanations. Looks like we could drop the fs/afs/rxrpc.c
chunk then.