linux-kernel - Re: [PATCH] tipc: avoid a clang -Wuninitialized warning

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Message-ID: <20190322161244.GG21978@archlinux-ryzen>
Date:   Fri, 22 Mar 2019 09:12:44 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jon Maloy <jon.maloy@...csson.com>,
        Ying Xue <ying.xue@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tuong Lien <tuong.t.lien@...tech.com.au>,
        LUU Duc Canh <canh.d.luu@...tech.com.au>,
        Tung Nguyen <tung.q.nguyen@...tech.com.au>,
        GhantaKrishnamurthy MohanKrishna 
        <mohan.krishna.ghanta.krishnamurthy@...csson.com>,
        netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tipc: avoid a clang -Wuninitialized warning

On Fri, Mar 22, 2019 at 03:18:13PM +0100, Arnd Bergmann wrote:
> clang notices that we pass 'maddr' into the tipc_bearer_xmit() function
> without having initialized it first:
> 
> net/tipc/node.c:831:6: error: variable 'maddr' is used uninitialized whenever 'if' condition is false
>       [-Werror,-Wsometimes-uninitialized]
>         if (!tipc_link_is_establishing(l)) {
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/tipc/node.c:847:46: note: uninitialized use occurs here
>         tipc_bearer_xmit(n->net, bearer_id, &xmitq, maddr);
>                                                     ^~~~~
> net/tipc/node.c:831:2: note: remove the 'if' if its condition is always true
>         if (!tipc_link_is_establishing(l)) {
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/tipc/node.c:821:31: note: initialize the variable 'maddr' to silence this warning
>         struct tipc_media_addr *maddr;
>                                      ^
>                                       = NULL
> 
> This is harmless because it won't use 'maddr' if the
> queue is empty, but it's better to make that explicit
> and not even call the function in that case.
> 
> As clang is able to inline the check, it then notices that
> the code is safe.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for looking into this and fixing it!

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  net/tipc/node.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/tipc/node.c b/net/tipc/node.c
> index 2dc4919ab23c..ca4cafd00a38 100644
> --- a/net/tipc/node.c
> +++ b/net/tipc/node.c
> @@ -844,7 +844,8 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id, bool delete)
>  	tipc_node_write_unlock(n);
>  	if (delete)
>  		tipc_mon_remove_peer(n->net, n->addr, old_bearer_id);
> -	tipc_bearer_xmit(n->net, bearer_id, &xmitq, maddr);
> +	if (!skb_queue_empty(&xmitq))
> +		tipc_bearer_xmit(n->net, bearer_id, &xmitq, maddr);
>  	tipc_sk_rcv(n->net, &le->inputq);
>  }
>  
> -- 
> 2.20.0
>