Subject: Re: [BUG] act_ife: sleeping functions called in atomic context

From: Jamal Hadi Salim <[email-masked]>
Date: Thu, 16 Jun 2016 20:38:31 -0400

On 16-06-16 05:43 PM, Cong Wang wrote:
> On Thu, Jun 16, 2016 at 1:50 PM, Alexey Khoroshilov
> <[email-masked]> wrote:
>> tcf_ife_init() contains a big chunk of code executed with
>> ife->tcf_lock spinlock held. But that code contains several calls
>> to sleeping functions:
>>    populate_metalist() and use_all_metadata()
>>      -> add_metainfo()
>>        -> find_ife_oplist(metaid)
>>          -> read_lock()
>>          -> try_module_get(o->owner)
>>        -> kzalloc(sizeof(*mi), GFP_KERNEL);
>
> Hmm, we don't need to hold that spinlock when we create a new ife action,
> since we haven't inserted it yet. We do need it when we modify an existing
> one. So I am thinking if we can refactor that code to avoid spinlock
> whenever possible.
>

Does attached (compile tested) patch help?

>>        -> ops->alloc(mi, metaval);
>>        -> module_put(ops->owner);
>>    _tcf_ife_cleanup()
>>      -> module_put()
>>
>> The same problem is actual for tcf_ife_cleanup() as well.
>>
>
> Huh? Both module_put() and kfree() should not sleep, right?
>

I dont think there is any sleeping there ;->

cheers,
jamal
diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
index 6bbc518..e341bef 100644
--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c
@@ -302,7 +302,9 @@ static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,
 		}
 	}
 
+	spin_lock_bh(&ife->tcf_lock);
 	list_add_tail(&mi->metalist, &ife->metalist);
+	spin_unlock_bh(&ife->tcf_lock);
 
 	return ret;
 }
@@ -474,7 +476,6 @@ static int tcf_ife_init(struct net *net, struct nlattr *nla,
 			saddr = nla_data(tb[TCA_IFE_SMAC]);
 	}
 
-	spin_lock_bh(&ife->tcf_lock);
 	ife->tcf_action = parm->action;
 
 	if (parm->flags & IFE_ENCODE) {
@@ -504,7 +505,6 @@ metadata_parse_err:
 			if (ret == ACT_P_CREATED)
 				_tcf_ife_cleanup(a, bind);
 
-			spin_unlock_bh(&ife->tcf_lock);
 			return err;
 		}
 
@@ -523,13 +523,10 @@ metadata_parse_err:
 			if (ret == ACT_P_CREATED)
 				_tcf_ife_cleanup(a, bind);
 
-			spin_unlock_bh(&ife->tcf_lock);
 			return err;
 		}
 	}
 
-	spin_unlock_bh(&ife->tcf_lock);
-
 	if (ret == ACT_P_CREATED)
 		tcf_hash_insert(tn, a);