netdev - Re: [PATCH] net: usb: pegasus: ignore the return value from set

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Date:   Sat, 14 Aug 2021 16:18:58 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Petko Manolov <petko.manolov@...sulko.com>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] net: usb: pegasus: ignore the return value from
 set_registers();

On 8/14/21 2:24 AM, Jakub Kicinski wrote:
> On Thu, 12 Aug 2021 11:23:51 +0300 Petko Manolov wrote:
>> The return value need to be either ignored or acted upon, otherwise 'deadstore'
>> clang check would yell at us.  I think it's better to just ignore what this
>> particular call of set_registers() returns.  The adapter defaults are sane and
>> it would be operational even if the register write fail.
>> 
>> Signed-off-by: Petko Manolov <petko.manolov@...sulko.com>
>> ---
>>  drivers/net/usb/pegasus.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/usb/pegasus.c b/drivers/net/usb/pegasus.c
>> index 652e9fcf0b77..49cfc720d78f 100644
>> --- a/drivers/net/usb/pegasus.c
>> +++ b/drivers/net/usb/pegasus.c
>> @@ -433,7 +433,7 @@ static int enable_net_traffic(struct net_device *dev, struct usb_device *usb)
>>  	data[2] = loopback ? 0x09 : 0x01;
>>  
>>  	memcpy(pegasus->eth_regs, data, sizeof(data));
>> -	ret = set_registers(pegasus, EthCtrl0, 3, data);
>> +	set_registers(pegasus, EthCtrl0, 3, data);
>>  
>>  	if (usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS ||
>>  	    usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS2 ||
> 
> This one is not added by the recent changes as I initially thought,
> the driver has always checked this return value. The recent changes
> did this:
> 
>          ret = set_registers(pegasus, EthCtrl0, 3, data);
>   
>          if (usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS ||
>              usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS2 ||
>              usb_dev_id[pegasus->dev_index].vendor == VENDOR_DLINK) {
>                  u16 auxmode;
> -               read_mii_word(pegasus, 0, 0x1b, &auxmode);
> +               ret = read_mii_word(pegasus, 0, 0x1b, &auxmode);
> +               if (ret < 0)
> +                       goto fail;
>                  auxmode |= 4;
>                  write_mii_word(pegasus, 0, 0x1b, &auxmode);
>          }
>   
> +       return 0;
> +fail:
> +       netif_dbg(pegasus, drv, pegasus->net, "%s failed\n", __func__);
>          return ret;
> }
> 
> now the return value of set_registeres() is ignored.
> 
> Seems like  a better fix would be to bring back the error checking,
> why not?
> 
> Please remember to add a fixes tag.
> 

Hi, Jakub!

I've suggested to handle this error, but Petko said that device won't 
stop working, it will just get in non-optimal state.

https://lore.kernel.org/lkml/YRF1t5kx6hTrv5LC@carbon/


With regards,
Pavel Skripkin