[PATCH net v2] connector: Change the judgment conditions for clearing proc_event_num_listeners

[PATCH net v2] connector: Change the judgment conditions for clearing proc_event_num_listeners

[wangkeqi]

From: wangkeqi <wangkeqiwang@didiglobal.com>

It is inaccurate to judge whether proc_event_num_listeners is
cleared by cn_netlink_send_mult returning -ESRCH.
In the case of stress-ng netlink-proc, -ESRCH will always be returned,
because netlink_broadcast_filtered will return -ESRCH,
which may cause stress-ng netlink-proc performance degradation.
Therefore, the judgment condition is modified to whether
there is a listener.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202401112259.b23a1567-oliver.sang@intel.com
Fixes: c46bfba133 ("connector: Fix proc_event_num_listeners count not cleared")
Signed-off-by: wangkeqi <wangkeqiwang@didiglobal.com>
Cc: fengwei.yin@intel.com
---
 drivers/connector/cn_proc.c   | 6 ++++--
 drivers/connector/connector.c | 6 ++++++
 include/linux/connector.h     | 1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index 3d5e6d705..b09f74ed3 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -108,8 +108,10 @@ static inline void send_msg(struct cn_msg *msg)
 		filter_data[1] = 0;
 	}
 
-	if (cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
-			     cn_filter, (void *)filter_data) == -ESRCH)
+	if (netlink_has_listeners(get_cdev_nls(), CN_IDX_PROC))
+		cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
+			     cn_filter, (void *)filter_data);
+	else
 		atomic_set(&proc_event_num_listeners, 0);
 
 	local_unlock(&local_event.lock);
diff --git a/drivers/connector/connector.c b/drivers/connector/connector.c
index 7f7b94f61..1b2cd410e 100644
--- a/drivers/connector/connector.c
+++ b/drivers/connector/connector.c
@@ -129,6 +129,12 @@ int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group,
 }
 EXPORT_SYMBOL_GPL(cn_netlink_send);
 
+struct sock *get_cdev_nls(void)
+{
+	return cdev.nls;
+}
+EXPORT_SYMBOL_GPL(get_cdev_nls);
+
 /*
  * Callback helper - queues work and setup destructor for given data.
  */
diff --git a/include/linux/connector.h b/include/linux/connector.h
index cec2d99ae..255466aea 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -127,6 +127,7 @@ int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid,
  */
 int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 group, gfp_t gfp_mask);
 
+struct sock *get_cdev_nls(void);
 int cn_queue_add_callback(struct cn_queue_dev *dev, const char *name,
 			  const struct cb_id *id,
 			  void (*callback)(struct cn_msg *, struct netlink_skb_parms *));
-- 
2.27.0

Re: [PATCH net v2] connector: Change the judgment conditions for clearing proc_event_num_listeners

[Florian Westphal]

wangkeqi <wangkeqi_chris@163.com> wrote:
> From: wangkeqi <wangkeqiwang@didiglobal.com>
> 
> It is inaccurate to judge whether proc_event_num_listeners is
> cleared by cn_netlink_send_mult returning -ESRCH.
> In the case of stress-ng netlink-proc, -ESRCH will always be returned,
> because netlink_broadcast_filtered will return -ESRCH,
> which may cause stress-ng netlink-proc performance degradation.
> Therefore, the judgment condition is modified to whether
> there is a listener.
> 
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202401112259.b23a1567-oliver.sang@intel.com
> Fixes: c46bfba133 ("connector: Fix proc_event_num_listeners count not cleared")
> Signed-off-by: wangkeqi <wangkeqiwang@didiglobal.com>
> Cc: fengwei.yin@intel.com
> ---
>  drivers/connector/cn_proc.c   | 6 ++++--
>  drivers/connector/connector.c | 6 ++++++
>  include/linux/connector.h     | 1 +
>  3 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index 3d5e6d705..b09f74ed3 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -108,8 +108,10 @@ static inline void send_msg(struct cn_msg *msg)
>  		filter_data[1] = 0;
>  	}
>  
> -	if (cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> -			     cn_filter, (void *)filter_data) == -ESRCH)
> +	if (netlink_has_listeners(get_cdev_nls(), CN_IDX_PROC))
> +		cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> +			     cn_filter, (void *)filter_data);
> +	else
>  		atomic_set(&proc_event_num_listeners, 0);

How is that serialized vs. cn_proc_mcast_ctl?

1. netlink_has_listeners() returns false
2.  other core handles PROC_CN_MCAST_LISTEN, atomic_inc called
3. This core (re)sets counter to 0, but there are listeners, so
    all functions that do

 if (atomic_read(&proc_event_num_listeners) < 1)
    return;

will not get enabled/remain disabled.

Probably better to add cn_netlink_has_listeners() function
and use that instead of the (inaccurate) counter?

Re:Re: [PATCH net v2] connector: Change the judgment conditions for clearing proc_event_num_listeners

[wangkeqi]

If cn_netlink_has_listeners() is used instead of proc_event_num_listeners, I think proc_event_num_listeners will be completely meaningless. 
I read the code and found that there is nothing wrong with cn_netlink_has_listeners as a judgment of whether to send msg. 
sock_close will update the listeners. The previous proc_event_num_listeners count was wrong, making it meaningless. 
But if I change it to cn_netlink_has_listeners, will it affect some low-probability scenarios?


At 2024-01-17 19:47:13, "Florian Westphal" <fw@strlen.de> wrote:
>wangkeqi <wangkeqi_chris@163.com> wrote:
>> From: wangkeqi <wangkeqiwang@didiglobal.com>
>> 
>> It is inaccurate to judge whether proc_event_num_listeners is
>> cleared by cn_netlink_send_mult returning -ESRCH.
>> In the case of stress-ng netlink-proc, -ESRCH will always be returned,
>> because netlink_broadcast_filtered will return -ESRCH,
>> which may cause stress-ng netlink-proc performance degradation.
>> Therefore, the judgment condition is modified to whether
>> there is a listener.
>> 
>> Reported-by: kernel test robot <oliver.sang@intel.com>
>> Closes: https://lore.kernel.org/oe-lkp/202401112259.b23a1567-oliver.sang@intel.com
>> Fixes: c46bfba133 ("connector: Fix proc_event_num_listeners count not cleared")
>> Signed-off-by: wangkeqi <wangkeqiwang@didiglobal.com>
>> Cc: fengwei.yin@intel.com
>> ---
>>  drivers/connector/cn_proc.c   | 6 ++++--
>>  drivers/connector/connector.c | 6 ++++++
>>  include/linux/connector.h     | 1 +
>>  3 files changed, 11 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
>> index 3d5e6d705..b09f74ed3 100644
>> --- a/drivers/connector/cn_proc.c
>> +++ b/drivers/connector/cn_proc.c
>> @@ -108,8 +108,10 @@ static inline void send_msg(struct cn_msg *msg)
>>  		filter_data[1] = 0;
>>  	}
>>  
>> -	if (cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
>> -			     cn_filter, (void *)filter_data) == -ESRCH)
>> +	if (netlink_has_listeners(get_cdev_nls(), CN_IDX_PROC))
>> +		cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
>> +			     cn_filter, (void *)filter_data);
>> +	else
>>  		atomic_set(&proc_event_num_listeners, 0);
>
>How is that serialized vs. cn_proc_mcast_ctl?
>
>1. netlink_has_listeners() returns false
>2.  other core handles PROC_CN_MCAST_LISTEN, atomic_inc called
>3. This core (re)sets counter to 0, but there are listeners, so
>    all functions that do
>
> if (atomic_read(&proc_event_num_listeners) < 1)
>    return;
>
>will not get enabled/remain disabled.
>
>Probably better to add cn_netlink_has_listeners() function
>and use that instead of the (inaccurate) counter?

Re: Re: [PATCH net v2] connector: Change the judgment conditions for clearing proc_event_num_listeners

[Florian Westphal]

wangkeqi <wangkeqi_chris@163.com> wrote:
> 
> If cn_netlink_has_listeners() is used instead of proc_event_num_listeners, I think proc_event_num_listeners will be completely meaningless. 
> I read the code and found that there is nothing wrong with cn_netlink_has_listeners as a judgment of whether to send msg. 
> sock_close will update the listeners. The previous proc_event_num_listeners count was wrong, making it meaningless. 
> But if I change it to cn_netlink_has_listeners, will it affect some low-probability scenarios?

Please avoid top-posting on netdev mailing list.

Yes, thats what I meant, replace proc_event_num_listeners.

I do not know what a 'low-probability scenarios' is.