net: stmmac: fix rx limit check in stmmac_rx_zc()

[ Upstream commit 8048168df5 ]

The extra "count >= limit" check in stmmac_rx_zc() is redundant and
has no effect because the value of "count" doesn't change after the
while condition at this point.

However, it can change after "read_again:" label:

        while (count < limit) {
            ...

            if (count >= limit)
                break;
    read_again:
            ...
            /* XSK pool expects RX frame 1:1 mapped to XSK buffer */
            if (likely(status & rx_not_ls)) {
                xsk_buff_free(buf->xdp);
                buf->xdp = NULL;
                dirty++;
                count++;
                goto read_again;
            }
            ...

This patch addresses the same issue previously resolved in stmmac_rx()
by commit fa02de9e75 ("net: stmmac: fix rx budget limit check").
The fix is the same: move the check after the label to ensure that it
bounds the goto loop.

Fixes: bba2556efa ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: Alexey Kodanev <aleksei.kodanev@bell-sw.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20251126104327.175590-1-aleksei.kodanev@bell-sw.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -5141,10 +5141,10 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 			len = 0;
 		}
 
+read_again:
 		if (count >= limit)
 			break;
 
-read_again:
 		buf1_len = 0;
 		entry = next_entry;
 		buf = &rx_q->buf_pool[entry];