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

From: Pablo Neira Ayuso <[email-masked]>
Date: Wed, 3 Dec 2014 13:19:49 +0100

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 <[email-masked]>
> ---
>  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.

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