linux-kernel - Re: [PATCH] rds: ib: force endiannes annotation

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Date:   Mon, 29 Apr 2019 12:00:06 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Nicholas Mc Guire <hofrat@...dl.org>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <rds-devel@....oracle.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rds: ib: force endiannes annotation

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.

-Ed