[PATCH net 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[PATCH net 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[KhaiWenTan]

The commit b8c43360f6e4 ("net: stmmac: No need to calculate speed divider
when offload is disabled") allows the "port_transmit_rate_kbps" to be
set to a value of 0, which is then passed to the "div_s64" function when
tc-cbs is disabled. This leads to a zero-division error.

When tc-cbs is disabled, the idleslope, sendslope, and credit values the
credit values are not required to be configured. Therefore, adding a return
statement after setting the txQ mode to DCB when tc-cbs is disabled would
prevent a zero-division error.

Fixes: b8c43360f6e4 ("net: stmmac: No need to calculate speed divider when offload is disabled")
Cc: <stable@vger.kernel.org>
Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
index 996f2bcd07a2..2c3fd9c66d14 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
@@ -392,10 +392,10 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 	} else if (!qopt->enable) {
 		ret = stmmac_dma_qmode(priv, priv->ioaddr, queue,
 				       MTL_QUEUE_DCB);
-		if (ret)
-			return ret;
+		if (!ret)
+			priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
 
-		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
+		return ret;
 	}
 
 	/* Final adjustments for HW */
-- 
2.25.1

Re: [PATCH net 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[Simon Horman]

On Thu, Sep 12, 2024 at 09:55:41AM +0800, KhaiWenTan wrote:
> The commit b8c43360f6e4 ("net: stmmac: No need to calculate speed divider
> when offload is disabled") allows the "port_transmit_rate_kbps" to be
> set to a value of 0, which is then passed to the "div_s64" function when
> tc-cbs is disabled. This leads to a zero-division error.
> 
> When tc-cbs is disabled, the idleslope, sendslope, and credit values the
> credit values are not required to be configured. Therefore, adding a return
> statement after setting the txQ mode to DCB when tc-cbs is disabled would
> prevent a zero-division error.
> 
> Fixes: b8c43360f6e4 ("net: stmmac: No need to calculate speed divider when offload is disabled")
> Cc: <stable@vger.kernel.org>
> Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> index 996f2bcd07a2..2c3fd9c66d14 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> @@ -392,10 +392,10 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
>  	} else if (!qopt->enable) {
>  		ret = stmmac_dma_qmode(priv, priv->ioaddr, queue,
>  				       MTL_QUEUE_DCB);
> -		if (ret)
> -			return ret;
> +		if (!ret)
> +			priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
>  
> -		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
> +		return ret;
>  	}

Thanks,

I agree with your analysis. But I think it would
be more idomatic to write it such that the main thread
of execution is the non-error path (in any case,
it makes it easier for me to understand the intent of the code.

What I am suggesting is this (extra context provided for clarity):

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
index 996f2bcd07a2..308ef4241768 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
@@ -392,14 +392,15 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 	} else if (!qopt->enable) {
 		ret = stmmac_dma_qmode(priv, priv->ioaddr, queue,
 				       MTL_QUEUE_DCB);
 		if (ret)
 			return ret;
 
 		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
+		return 0;
 	}
 
 	/* Final adjustments for HW */
 	value = div_s64(qopt->idleslope * 1024ll * ptr, port_transmit_rate_kbps);
 	priv->plat->tx_queues_cfg[queue].idle_slope = value & GENMASK(31, 0);
 
 	value = div_s64(-qopt->sendslope * 1024ll * ptr, port_transmit_rate_kbps);

Re: [PATCH net 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[Simon Horman]

On Thu, Sep 12, 2024 at 04:37:30PM +0100, Simon Horman wrote:
> On Thu, Sep 12, 2024 at 09:55:41AM +0800, KhaiWenTan wrote:
> > The commit b8c43360f6e4 ("net: stmmac: No need to calculate speed divider
> > when offload is disabled") allows the "port_transmit_rate_kbps" to be
> > set to a value of 0, which is then passed to the "div_s64" function when
> > tc-cbs is disabled. This leads to a zero-division error.
> > 
> > When tc-cbs is disabled, the idleslope, sendslope, and credit values the
> > credit values are not required to be configured. Therefore, adding a return
> > statement after setting the txQ mode to DCB when tc-cbs is disabled would
> > prevent a zero-division error.
> > 
> > Fixes: b8c43360f6e4 ("net: stmmac: No need to calculate speed divider when offload is disabled")
> > Cc: <stable@vger.kernel.org>
> > Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> > Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> > Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>

...

One more thing, if you do post an updated patch, please
be sure to wait until 24h after the original patch was posted.

https://docs.kernel.org/process/maintainer-netdev.html

Re: [PATCH net 1/1] net: stmmac: Fix zero-division error when disabling tc cbs

[Tan, Khai Wen]

On 12/9/2024 11:39 pm, Simon Horman wrote:
> On Thu, Sep 12, 2024 at 04:37:30PM +0100, Simon Horman wrote:
>> On Thu, Sep 12, 2024 at 09:55:41AM +0800, KhaiWenTan wrote:
>>> The commit b8c43360f6e4 ("net: stmmac: No need to calculate speed divider
>>> when offload is disabled") allows the "port_transmit_rate_kbps" to be
>>> set to a value of 0, which is then passed to the "div_s64" function when
>>> tc-cbs is disabled. This leads to a zero-division error.
>>>
>>> When tc-cbs is disabled, the idleslope, sendslope, and credit values the
>>> credit values are not required to be configured. Therefore, adding a return
>>> statement after setting the txQ mode to DCB when tc-cbs is disabled would
>>> prevent a zero-division error.
>>>
>>> Fixes: b8c43360f6e4 ("net: stmmac: No need to calculate speed divider when offload is disabled")
>>> Cc: <stable@vger.kernel.org>
>>> Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
>>> Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
>>> Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
> ...
>
> One more thing, if you do post an updated patch, please
> be sure to wait until 24h after the original patch was posted.
>
> https://docs.kernel.org/process/maintainer-netdev.html

Hi Simon,

Thanks for the clarification. Will be updating a version 2 for this patch.