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

On Sat, Jun 3, 2017 at 7:35 PM, Colin Ian King [off-list ref] wrote:

On 03/06/17 16:55, Andy Shevchenko wrote:

quoted

On Fri, Jun 2, 2017 at 5:58 PM, Colin King [off-list ref] wrote:

quoted

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.

quoted

        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;

Looks cleaner, though I was thinking about changing type of entry as
Julia suggested. Needs to be checked carefully anyway.

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

With refined grep I'e got only 56 so far. And I see it's spread only
in 45 modules, most cases are single use cases.
So, I hardly can tell this is an idiom in kernel.

-- 
With Best Regards,
Andy Shevchenko