linux-kernel - Re: [PATCH] xen/netback: fix build warning

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Message-ID: <f1c89855-22d4-8605-e73e-6658aef148f9@suse.com>
Date:   Wed, 7 Dec 2022 11:18:58 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Ross Lagerwall <ross.lagerwall@...rix.com>
Subject: Re: [PATCH] xen/netback: fix build warning

On 07.12.22 10:25, Jan Beulich wrote:
> On 07.12.2022 08:23, Juergen Gross wrote:
>> Commit ad7f402ae4f4 ("xen/netback: Ensure protocol headers don't fall in
>> the non-linear area") introduced a (valid) build warning.
>>
>> Fix it.
>>
>> Fixes: ad7f402ae4f4 ("xen/netback: Ensure protocol headers don't fall in the non-linear area")
>> Signed-off-by: Juergen Gross <jgross@...e.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@...e.com>
> 
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -530,7 +530,7 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
>>   	const bool sharedslot = nr_frags &&
>>   				frag_get_pending_idx(&shinfo->frags[0]) ==
>>   				    copy_pending_idx(skb, copy_count(skb) - 1);
>> -	int i, err;
>> +	int i, err = 0;
>>   
>>   	for (i = 0; i < copy_count(skb); i++) {
>>   		int newerr;
> 
> I'm afraid other logic (below here) is now slightly wrong as well, in
> particular
> 
> 				/* If the mapping of the first frag was OK, but
> 				 * the header's copy failed, and they are
> 				 * sharing a slot, send an error
> 				 */
> 				if (i == 0 && !first_shinfo && sharedslot)
> 					xenvif_idx_release(queue, pending_idx,
> 							   XEN_NETIF_RSP_ERROR);
> 				else
> 					xenvif_idx_release(queue, pending_idx,
> 							   XEN_NETIF_RSP_OKAY);
> 
> which looks to be intended to deal with _only_ failure of the one shared
> part of the header, whereas "err" now can indicate an error on any earlier
> part as well.

The comment at the end of that loop seems to imply this is the desired
behavior:

		/* Remember the error: invalidate all subsequent fragments. */
		err = newerr;
	}


Juergen


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