linux-kernel - Re: [PATCH RFC 9/9] sunrpc: don't upgrade passive net reference in xs_create

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Message-ID: <1b2824d29af8b23ed59db976420e048eff875159.camel@kernel.org>
Date: Mon, 17 Mar 2025 17:36:02 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Trond Myklebust <trondmy@...merspace.com>, "horms@...nel.org"	
 <horms@...nel.org>, "davem@...emloft.net" <davem@...emloft.net>, 
 "chuck.lever@...cle.com"	 <chuck.lever@...cle.com>, "okorniev@...hat.com"
 <okorniev@...hat.com>,  "anna@...nel.org"	 <anna@...nel.org>,
 "kuba@...nel.org" <kuba@...nel.org>, "tom@...pey.com"	 <tom@...pey.com>,
 "Dai.Ngo@...cle.com" <Dai.Ngo@...cle.com>, "neilb@...e.de"	
 <neilb@...e.de>, "edumazet@...gle.com" <edumazet@...gle.com>, 
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Cc: "josef@...icpanda.com" <josef@...icpanda.com>, 
 "linux-nfs@...r.kernel.org"
	 <linux-nfs@...r.kernel.org>, "bcodding@...hat.com" <bcodding@...hat.com>, 
 "linux-kernel@...r.kernel.org"
	 <linux-kernel@...r.kernel.org>, "netdev@...r.kernel.org"
	 <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC 9/9] sunrpc: don't upgrade passive net reference in
 xs_create_sock

On Mon, 2025-03-17 at 21:28 +0000, Trond Myklebust wrote:
> On Mon, 2025-03-17 at 17:00 -0400, Jeff Layton wrote:
> > With the move to having sunrpc client xprts not hold active
> > references
> > to the net namespace, there is no need to upgrade the socket's
> > reference
> > in xs_create_sock. Just keep the passive reference instead.
> > 
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > ---
> >  net/sunrpc/xprtsock.c | 3 ---
> >  1 file changed, 3 deletions(-)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index
> > 83cc095846d356f24aed26e2f98525662a6cff1f..0c3d7552f772d6f8477a3aed8f0
> > c513b62cdf589 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -1941,9 +1941,6 @@ static struct socket *xs_create_sock(struct
> > rpc_xprt *xprt,
> >  		goto out;
> >  	}
> >  
> > -	if (protocol == IPPROTO_TCP)
> > -		sk_net_refcnt_upgrade(sock->sk);
> > -
> >  	filp = sock_alloc_file(sock, O_NONBLOCK, NULL);
> >  	if (IS_ERR(filp))
> >  		return ERR_CAST(filp);
> > 
> 
> Is this not going to reintroduce the bug described by
> https://lore.kernel.org/netdev/67b72aeb.050a0220.14d86d.0283.GAE@google.com/T/#u
> ?
> 
> As I understand it, the problem has nothing to do with whether or not
> NFS or the RPC layer holds a reference to the net namespace, but rather
> whether there are still packets in the socket queues at the time when
> that net namespace is being freed.
> 
> 

I don't think so. That syzkaller report was closed by this patch:

    5c70eb5c593d net: better track kernel sockets lifetime

That says:

    "To fix this, make sure that kernel sockets own a reference on net
passive."

With this, we still do keep a passive reference on the net in the
socket, which I think is enough.

That said, I'd appreciate a look at this from the netdev folks.
-- 
Jeff Layton <jlayton@...nel.org>