[PATCH net-next] net: stmmac: clean up impossible condition

[PATCH net-next] net: stmmac: clean up impossible condition

[Dan Carpenter]

This code works but it has a static checker warning:

    drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:1687 init_dma_rx_desc_rings()
    warn: always true condition '(queue >= 0) => (0-u32max >= 0)'

Obviously, it makes no sense to check if an unsigned int is >= 0.  What
prevents this code from being a forever loop is that later there is a
separate check for if (queue == 0).

The "queue" variable is less than MTL_MAX_RX_QUEUES (8) so it can easily
fit in an int type.  Any larger value for "queue" would lead to an array
overflow when we assign "rx_q = &priv->rx_queue[queue]".

Fixes: de0b90e52a11 ("net: stmmac: rearrange RX and TX desc init into per-queue basis")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
This code is old so the patch could apply to net, but it's a cleanup and
not a bugfix.

 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index cf4e077d21ff..932f444d0d68 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1668,7 +1668,7 @@ static int init_dma_rx_desc_rings(struct net_device *dev, gfp_t flags)
 {
 	struct stmmac_priv *priv = netdev_priv(dev);
 	u32 rx_count = priv->plat->rx_queues_to_use;
-	u32 queue;
+	int queue;
 	int ret;
 
 	/* RX INITIALIZATION */
@@ -1695,9 +1695,6 @@ static int init_dma_rx_desc_rings(struct net_device *dev, gfp_t flags)
 		rx_q->buf_alloc_num = 0;
 		rx_q->xsk_pool = NULL;
 
-		if (queue == 0)
-			break;
-
 		queue--;
 	}
 
-- 
2.20.1

Re: [PATCH net-next] net: stmmac: clean up impossible condition

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 16 Mar 2022 11:37:44 +0300 you wrote:
> This code works but it has a static checker warning:
> 
>     drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:1687 init_dma_rx_desc_rings()
>     warn: always true condition '(queue >= 0) => (0-u32max >= 0)'
> 
> Obviously, it makes no sense to check if an unsigned int is >= 0.  What
> prevents this code from being a forever loop is that later there is a
> separate check for if (queue == 0).
> 
> [...]

Here is the summary with links:
  - [net-next] net: stmmac: clean up impossible condition
    https://git.kernel.org/netdev/net-next/c/58e06d05d43a

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html