From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 21 Jul 2020 05:28:21 +0000
Subject: Re: [PATCH 02/24] bpfilter: fix up a sparse annotation
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To: Christoph Hellwig <hch@lst.de>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>, Eric Dumazet <edumazet@google.com>, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, linux-sctp@vger.kernel.org, linux-hams@vger.kernel.org, linux-bluetooth@vger.kernel.org, bridge@lists.linux-foundation.org, linux-can@vger.kernel.org, dccp@vger.kernel.org, linux-decnet-user@lists.sourceforge.net, linux-wpan@vger.kernel.org, linux-s390@vger.kernel.org, mptcp@lists.01.org, lvs-devel@vger.kernel.org, rds-devel@oss.oracle.com, linux-afs@lists.infradead.org, tipc-discussion@lists.sourceforge.net, linux-x25@vger.kernel.org

On Tue, Jul 21, 2020 at 07:23:26AM +0200, Christoph Hellwig wrote:
> On Tue, Jul 21, 2020 at 04:40:16AM +0200, Luc Van Oostenryck wrote:
> > >  	req.pid = current->pid;
> > >  	req.cmd = optname;
> > > -	req.addr = (long __force __user)optval;
> > > +	req.addr = (__force long)optval;
> > 
> > For casts to integers, even '__force' is not needed (since integers
> > can't be dereferenced, the concept of address-space is meaningless
> > for them, so it's never useful to warn when it's dropped and
> > '__force' is thus not needed).
> 
> That's what I thought. but if I remove it here I actually do get a
> warning:
> 
> CHECK   net/bpfilter/bpfilter_kern.c
> net/bpfilter/bpfilter_kern.c:52:21: warning: cast removes address space '__user' of expression

Cast to unsigned long.  Or to uintptr_t if you want to be fancy.