linux-kernel - Re: [2.6.21 patch] net/sunrpc/svcsock.c: fix a check

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Message-Id: <20070319233837.38f1aab7.akpm@linux-foundation.org>
Date:	Mon, 19 Mar 2007 23:38:37 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Adrian Bunk <bunk@...sta.de>
Cc:	Neil Brown <neilb@...e.de>, nfs@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6.21 patch] net/sunrpc/svcsock.c: fix a check

On Mon, 19 Mar 2007 10:33:42 +0100 Adrian Bunk <bunk@...sta.de> wrote:

> The return value of kernel_recvmsg() should be assigned to "err", not 
> compared with the random value of a never initialized "err"
> (and the "< 0" check wrongly always returned false since == comparisons 
> never have a result < 0).
> 
> Spotted by the Coverity checker.
> 
> Signed-off-by: Adrian Bunk <bunk@...sta.de>
> 
> ---
> --- linux-2.6.21-rc3-mm2/net/sunrpc/svcsock.c.old	2007-03-19 09:44:40.000000000 +0100
> +++ linux-2.6.21-rc3-mm2/net/sunrpc/svcsock.c	2007-03-19 09:45:18.000000000 +0100
> @@ -779,8 +779,8 @@ svc_udp_recvfrom(struct svc_rqst *rqstp)
>  	}
>  
>  	clear_bit(SK_DATA, &svsk->sk_flags);
> -	while ((err == kernel_recvmsg(svsk->sk_sock, &msg, NULL,
> -				      0, 0, MSG_PEEK | MSG_DONTWAIT)) < 0 ||
> +	while ((err = kernel_recvmsg(svsk->sk_sock, &msg, NULL,
> +				     0, 0, MSG_PEEK | MSG_DONTWAIT)) < 0 ||
>  	       (skb = skb_recv_datagram(svsk->sk_sk, 0, 1, &err)) == NULL) {
>  		if (err == -EAGAIN) {
>  			svc_sock_received(svsk);

Cute.  The compiler must have decided to apply the "(a==b) can never be
less than zero" optimisation before performing uninitialised variable
analysis.

Neil, this one needs runtime testing before we can apply it to 2.6.21, I
think.
-
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