netdev - Re: [PATCH net-next] net: remove redundant NULL check in remove_xps

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Date: Wed, 26 Jul 2023 10:25:13 +0800
From: shaozhengchao <shaozhengchao@...wei.com>
To: Simon Horman <simon.horman@...igine.com>
CC: <netdev@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <kuniyu@...zon.com>,
	<liuhangbin@...il.com>, <jiri@...nulli.us>, <hkallweit1@...il.com>,
	<andy.ren@...cruise.com>, <weiyongjun1@...wei.com>, <yuehaibing@...wei.com>
Subject: Re: [PATCH net-next] net: remove redundant NULL check in
 remove_xps_queue()



On 2023/7/25 15:04, Simon Horman wrote:
> On Mon, Jul 24, 2023 at 10:37:35AM +0800, Zhengchao Shao wrote:
>> There are currently two paths that call remove_xps_queue():
>> 1. __netif_set_xps_queue -> remove_xps_queue
>> 2. clean_xps_maps -> remove_xps_queue_cpu -> remove_xps_queue
>> There is no need to check dev_maps in remove_xps_queue() because
>> dev_maps has been checked on these two paths.
>>
>> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
> 
> I have verified the reasoning above is correct.
> I am, however, slightly less sure that this is a good idea.
> 
Since commit 044ab86d431b("net: move the xps maps to an array") and
commit 867d0ad476db("net: fix XPS static_key accounting are
incorporated"), it is meaningless to reserve the null judgment. Perhaps
after removing this null check, add comment, like
/ * the caller must make sure that dev_maps != NULL */ ?
Thank you.

Zhengchao Shao
>> ---
>>   net/core/dev.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index f95e0674570f..76a91b849829 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2384,8 +2384,7 @@ static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
>>   	struct xps_map *map = NULL;
>>   	int pos;
>>   
>> -	if (dev_maps)
>> -		map = xmap_dereference(dev_maps->attr_map[tci]);
>> +	map = xmap_dereference(dev_maps->attr_map[tci]);
>>   	if (!map)
>>   		return false;
>>   
>> -- 
>> 2.34.1
>>