Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Colin Ian King]

On 03/06/17 16:55, Andy Shevchenko wrote:
> On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@xxxxxxxxxxxxx> wrote:
>> The current comparison of entry < 0 will never be true since entry is an
>> unsigned integer. Cast entry to an int to ensure -ve error return values
>> from the call to jumbo_frm are correctly being caught.
> 
>>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>>                                          DWMAC_CORE_4_00)) {
>>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>> -               if (unlikely(entry < 0))
>> +               if (unlikely((int)entry < 0))
> 
> It feels like a hiding some other issue.
> 

The alternative is:

		int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
		if (unlikely(rc < 0))
			goto dma_map_err;

		entry = rc;

however, that is effectively the same. The cast I'm using is a well used
idiom in the kernel, it used in almost a hundred similar cases.

git grep "< 0" | grep "(int)" | wc -l
95

Colin