From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicholas Mc Guire Subject: Re: [PATCH] rds: ib: force endiannes annotation Date: Mon, 29 Apr 2019 13:18:36 +0200 Message-ID: <20190429111836.GA17830@osadl.at> References: <1556518178-13786-1-git-send-email-hofrat@osadl.org> <20443fd3-bd1e-9472-8ca3-e3014e59f249@solarflare.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20443fd3-bd1e-9472-8ca3-e3014e59f249@solarflare.com> Sender: linux-kernel-owner@vger.kernel.org To: Edward Cree Cc: Nicholas Mc Guire , Santosh Shilimkar , "David S. Miller" , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org List-Id: linux-rdma@vger.kernel.org On Mon, Apr 29, 2019 at 12:00:06PM +0100, Edward Cree wrote: > On 29/04/2019 07:09, Nicholas Mc Guire wrote: > > diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c > > index 7055985..a070a2d 100644 > > --- a/net/rds/ib_recv.c > > +++ b/net/rds/ib_recv.c > > @@ -824,7 +824,7 @@ static void rds_ib_cong_recv(struct rds_connection *conn, > > } > > > > /* the congestion map is in little endian order */ > > - uncongested = le64_to_cpu(uncongested); > > + uncongested = le64_to_cpu((__force __le64)uncongested); > > > > rds_cong_map_updated(map, uncongested); > > } > Again, a __force cast doesn't seem necessary here.  It looks like the >  code is just using the wrong types; if all of src, dst and uncongested >  were __le64 instead of uint64_t, and the last two lines replaced with >  rds_cong_map_updated(map, le64_to_cpu(uncongested)); then the semantics >  would be kept with neither sparse errors nor __force. > > __force is almost never necessary and mostly just masks other bugs or >  endianness confusion in the surrounding code.  Instead of adding a >  __force, either fix the code to be sparse-clean or leave the sparse >  warning in place so that future developers know there's something not >  right. > changing uncongested to __le64 is not an option here - it would only move the sparse warnings to those other locatoins where the ports that became uncongested are being or'ed into uncongested. I'm not using __force as the prime way to silence sparse - I try to find an alternative first - the problem is in line 805 for (k = 0; k < to_copy; k += 8) { /* Record ports that became uncongested, ie * bits that changed from 0 to 1. */ uncongested |= ~(*src) & *dst; *dst++ = *src++; } And in this case the endianness handling does seem right. But ok with me to leave it in as it is - if you think that the __force here is not justified. thanks for your comments and notably the explainations ! thx! hofrat alternative