[Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[Cong Wang]

Laura reported a sleep-in-atomic kernel warning inside
tcf_act_police_init() which calls gen_replace_estimator() with
spinlock protection.

It is not necessary in this case, we already have RTNL lock here
so it is enough to protect concurrent writers. For the reader,
i.e. tcf_act_police(), it needs to make decision based on this
rate estimator, in the worst case we drop more/less packets than
necessary while changing the rate in parallel, it is still acceptable.

Reported-by: Laura Abbott <labbott@redhat.com>
Reported-by: Nick Huber <nicholashuber@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/sched/act_police.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index f42008b..b062bc8 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -132,21 +132,21 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
 		}
 	}
 
-	spin_lock_bh(&police->tcf_lock);
 	if (est) {
 		err = gen_replace_estimator(&police->tcf_bstats, NULL,
 					    &police->tcf_rate_est,
 					    &police->tcf_lock,
 					    NULL, est);
 		if (err)
-			goto failure_unlock;
+			goto failure;
 	} else if (tb[TCA_POLICE_AVRATE] &&
 		   (ret == ACT_P_CREATED ||
 		    !gen_estimator_active(&police->tcf_rate_est))) {
 		err = -EINVAL;
-		goto failure_unlock;
+		goto failure;
 	}
 
+	spin_lock_bh(&police->tcf_lock);
 	/* No failure allowed after this point */
 	police->tcfp_mtu = parm->mtu;
 	if (police->tcfp_mtu == 0) {
@@ -192,8 +192,6 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
 
 	return ret;
 
-failure_unlock:
-	spin_unlock_bh(&police->tcf_lock);
 failure:
 	qdisc_put_rtab(P_tab);
 	qdisc_put_rtab(R_tab);
-- 
2.5.5

Re: [Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[Yuval Shaia]

On Tue, Jun 13, 2017 at 01:36:24PM -0700, Cong Wang wrote:
> Laura reported a sleep-in-atomic kernel warning inside

Since you added a Reported-by tag below i don't see a reason to
specifically mention it in commit log message.

> tcf_act_police_init() which calls gen_replace_estimator() with
> spinlock protection.
> 
> It is not necessary in this case, we already have RTNL lock here
> so it is enough to protect concurrent writers. For the reader,
> i.e. tcf_act_police(), it needs to make decision based on this
> rate estimator, in the worst case we drop more/less packets than
> necessary while changing the rate in parallel, it is still acceptable.
> 
> Reported-by: Laura Abbott <labbott@redhat.com>
> Reported-by: Nick Huber <nicholashuber@gmail.com>
> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/sched/act_police.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> index f42008b..b062bc8 100644
> --- a/net/sched/act_police.c
> +++ b/net/sched/act_police.c
> @@ -132,21 +132,21 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
>  		}
>  	}
>  
> -	spin_lock_bh(&police->tcf_lock);
>  	if (est) {
>  		err = gen_replace_estimator(&police->tcf_bstats, NULL,
>  					    &police->tcf_rate_est,
>  					    &police->tcf_lock,
>  					    NULL, est);
>  		if (err)
> -			goto failure_unlock;
> +			goto failure;
>  	} else if (tb[TCA_POLICE_AVRATE] &&
>  		   (ret == ACT_P_CREATED ||
>  		    !gen_estimator_active(&police->tcf_rate_est))) {
>  		err = -EINVAL;
> -		goto failure_unlock;
> +		goto failure;
>  	}
>  
> +	spin_lock_bh(&police->tcf_lock);
>  	/* No failure allowed after this point */
>  	police->tcfp_mtu = parm->mtu;
>  	if (police->tcfp_mtu == 0) {
> @@ -192,8 +192,6 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
>  
>  	return ret;
>  
> -failure_unlock:
> -	spin_unlock_bh(&police->tcf_lock);
>  failure:
>  	qdisc_put_rtab(P_tab);
>  	qdisc_put_rtab(R_tab);
> -- 
> 2.5.5
> 

Re: [Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[Cong Wang]

On Tue, Jun 13, 2017 at 1:40 PM, Yuval Shaia <yuval.shaia@oracle.com> wrote:
> On Tue, Jun 13, 2017 at 01:36:24PM -0700, Cong Wang wrote:
>> Laura reported a sleep-in-atomic kernel warning inside
>
> Since you added a Reported-by tag below i don't see a reason to
> specifically mention it in commit log message.

If you have faith in this, feel free to update netdev-FAQ.txt to save
your time and others' time in the future.

Thanks.

Re: [Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[David Miller]

From: Yuval Shaia <yuval.shaia@oracle.com>
Date: Tue, 13 Jun 2017 23:40:41 +0300

> On Tue, Jun 13, 2017 at 01:36:24PM -0700, Cong Wang wrote:
>> Laura reported a sleep-in-atomic kernel warning inside
> 
> Since you added a Reported-by tag below i don't see a reason to
> specifically mention it in commit log message.

That doesn't make any sense at all.

Part of telling the story is saying that someone reported a specific
kind of issue, and here is the problem, and here is how we solved it.

Just because there's a reported-by tag doesn't mean it's superfluous.

Re: [Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[Jamal Hadi Salim]

On 17-06-13 04:36 PM, Cong Wang wrote:
> Laura reported a sleep-in-atomic kernel warning inside
> tcf_act_police_init() which calls gen_replace_estimator() with
> spinlock protection.
> 
> It is not necessary in this case, we already have RTNL lock here
> so it is enough to protect concurrent writers. For the reader,
> i.e. tcf_act_police(), it needs to make decision based on this
> rate estimator, in the worst case we drop more/less packets than
> necessary while changing the rate in parallel, it is still acceptable.
> 
> Reported-by: Laura Abbott <labbott@redhat.com>
> Reported-by: Nick Huber <nicholashuber@gmail.com>
> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>   net/sched/act_police.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> index f42008b..b062bc8 100644
> --- a/net/sched/act_police.c
> +++ b/net/sched/act_police.c
> @@ -132,21 +132,21 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
>   		}
>   	}
>   
> -	spin_lock_bh(&police->tcf_lock);
>   	if (est) {
>   		err = gen_replace_estimator(&police->tcf_bstats, NULL,
>   					    &police->tcf_rate_est,
>   					    &police->tcf_lock,
>   					    NULL, est);
>   		if (err)
> -			goto failure_unlock;
> +			goto failure;
>   	} else if (tb[TCA_POLICE_AVRATE] &&
>   		   (ret == ACT_P_CREATED ||
>   		    !gen_estimator_active(&police->tcf_rate_est))) {
>   		err = -EINVAL;
> -		goto failure_unlock;
> +		goto failure;
>   	}
>   
> +	spin_lock_bh(&police->tcf_lock);
>   	/* No failure allowed after this point */
>   	police->tcfp_mtu = parm->mtu;
>   	if (police->tcfp_mtu == 0) {
> @@ -192,8 +192,6 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
>   
>   	return ret;
>   
> -failure_unlock:
> -	spin_unlock_bh(&police->tcf_lock);
>   failure:
>   	qdisc_put_rtab(P_tab);
>   	qdisc_put_rtab(R_tab);
> 


Looks good to me.

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

cheers,
jamal

Re: [Patch net] net_sched: move tcf_lock down after gen_replace_estimator()

[David Miller]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Tue, 13 Jun 2017 13:36:24 -0700

> Laura reported a sleep-in-atomic kernel warning inside
> tcf_act_police_init() which calls gen_replace_estimator() with
> spinlock protection.
> 
> It is not necessary in this case, we already have RTNL lock here
> so it is enough to protect concurrent writers. For the reader,
> i.e. tcf_act_police(), it needs to make decision based on this
> rate estimator, in the worst case we drop more/less packets than
> necessary while changing the rate in parallel, it is still acceptable.
> 
> Reported-by: Laura Abbott <labbott@redhat.com>
> Reported-by: Nick Huber <nicholashuber@gmail.com>
> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied, thanks.