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From:   "Jonathan Lemon" <jonathan.lemon@gmail.com>
To:     "Nathan Chancellor" <natechancellor@gmail.com>
Cc:     "=?utf-8?b?QmrDtnJuIFTDtnBlbA==?=" <bjorn.topel@intel.com>,
        "Magnus Karlsson" <magnus.karlsson@intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        "Alexei Starovoitov" <ast@kernel.org>,
        "Daniel Borkmann" <daniel@iogearbox.net>,
        "Jakub Kicinski" <jakub.kicinski@netronome.com>,
        "Jesper Dangaard Brouer" <hawk@kernel.org>,
        "John Fastabend" <john.fastabend@gmail.com>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        xdp-newbies@vger.kernel.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        "Nick Desaulniers" <ndesaulniers@google.com>,
        "Nathan Huckleberry" <nhuck@google.com>
Subject: Re: [PATCH] xsk: Properly terminate assignment in
 xskq_produce_flush_desc
Date:   Tue, 25 Jun 2019 12:46:02 -0700
Message-ID: <34F07894-FDE7-44F8-B7F2-E2003D550AD2@gmail.com>
In-Reply-To: <20190625182352.13918-1-natechancellor@gmail.com>
References: <20190625182352.13918-1-natechancellor@gmail.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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On 25 Jun 2019, at 11:23, Nathan Chancellor wrote:

> Clang warns:
>
> In file included from net/xdp/xsk_queue.c:10:
> net/xdp/xsk_queue.h:292:2: warning: expression result unused
> [-Wunused-value]
>         WRITE_ONCE(q->ring->producer, q->prod_tail);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/compiler.h:284:6: note: expanded from macro 'WRITE_ONCE'
>         __u.__val;                                      \
>         ~~~ ^~~~~
> 1 warning generated.
>
> The q->prod_tail assignment has a comma at the end, not a semi-colon.
> Fix that so clang no longer warns and everything works as expected.
>
> Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
> Link: https://github.com/ClangBuiltLinux/linux/issues/544
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Nice find.

Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>


> ---
>  net/xdp/xsk_queue.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index 88b9ae24658d..cba4a640d5e8 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -288,7 +288,7 @@ static inline void xskq_produce_flush_desc(struct 
> xsk_queue *q)
>  	/* Order producer and data */
>  	smp_wmb(); /* B, matches C */
>
> -	q->prod_tail = q->prod_head,
> +	q->prod_tail = q->prod_head;
>  	WRITE_ONCE(q->ring->producer, q->prod_tail);
>  }
>
> -- 
> 2.22.0