netdev - Re: [patch net-next 3/6] net_sched: cls_bpf: remove faulty use of list_for_each_entry

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Message-ID: <20141203132142.GG1860@nanopsycho.orion>
Date:	Wed, 3 Dec 2014 14:21:42 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com
Subject: Re: [patch net-next 3/6] net_sched: cls_bpf: remove faulty use of
 list_for_each_entry_rcu

Wed, Dec 03, 2014 at 01:19:49PM CET, pablo@...filter.org wrote:
>On Tue, Dec 02, 2014 at 06:00:33PM +0100, Jiri Pirko wrote:
>> rcu variant is not correct here. The code is called by updater (rtnl
>> lock is held), not by reader (no rcu_read_lock is held).
>> 
>> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
>> ---
>>  net/sched/cls_bpf.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
>> index cbfaf6f..d0de979 100644
>> --- a/net/sched/cls_bpf.c
>> +++ b/net/sched/cls_bpf.c
>> @@ -141,7 +141,7 @@ static unsigned long cls_bpf_get(struct tcf_proto *tp, u32 handle)
>>  	if (head == NULL)
>>  		return 0UL;
>>  
>> -	list_for_each_entry_rcu(prog, &head->plist, link) {
>> +	list_for_each_entry(prog, &head->plist, link) {
>>  		if (prog->handle == handle) {
>>  			ret = (unsigned long) prog;
>>  			break;
>> @@ -337,7 +337,7 @@ static void cls_bpf_walk(struct tcf_proto *tp, struct tcf_walker *arg)
>>  	struct cls_bpf_head *head = rtnl_dereference(tp->root);
>>  	struct cls_bpf_prog *prog;
>>  
>> -	list_for_each_entry_rcu(prog, &head->plist, link) {
>> +	list_for_each_entry(prog, &head->plist, link) {
>
>We still need the _rcu here in the walk path. IIRC, this is called from the
>dump path and we hold no rtnl_lock there.

It is called from tc_dump_tfilter only. And tc_dump_tfilter is always
called with rtnl_lock

>
>>  		if (arg->count < arg->skip)
>>  			goto skip;
>>  		if (arg->fn(tp, (unsigned long) prog, arg) < 0) {
>> -- 
>> 1.9.3
>> 
>> --
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