[PATCH net-next] net: remove redundant NULL check in remove_xps_queue()

[PATCH net-next] net: remove redundant NULL check in remove_xps_queue()

[Zhengchao Shao]

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@huawei.com>
---
 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

Re: [PATCH net-next] net: remove redundant NULL check in remove_xps_queue()

[Simon Horman]

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@huawei.com>

I have verified the reasoning above is correct.
I am, however, slightly less sure that this is a good idea.

> ---
>  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
> 

Re: [PATCH net-next] net: remove redundant NULL check in remove_xps_queue()

[shaozhengchao]

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@huawei.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
>>

Re: [PATCH net-next] net: remove redundant NULL check in remove_xps_queue()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 24 Jul 2023 10:37:35 +0800 you 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@huawei.com>
> 
> [...]

Here is the summary with links:
  - [net-next] net: remove redundant NULL check in remove_xps_queue()
    https://git.kernel.org/netdev/net-next/c/f080864a9d90

You are awesome, thank you!
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