netdev - Re: [PATCH net-next] bpf: Remove unused but set variable in __bpf_lru_list_shrink

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Message-ID: <20170111005700.GB15234@kafai-mba.local>
Date:   Tue, 10 Jan 2017 16:57:00 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Tobias Klauser <tklauser@...tanz.ch>, <netdev@...r.kernel.org>,
        <ast@...nel.org>
Subject: Re: [PATCH net-next] bpf: Remove unused but set variable in
 __bpf_lru_list_shrink_inactive()

On Tue, Jan 10, 2017 at 04:25:23PM -0800, Alexei Starovoitov wrote:
> On Tue, Jan 10, 2017 at 03:02:07PM +0100, Tobias Klauser wrote:
> > Remove the unused but set variable 'first_node' in
> > __bpf_lru_list_shrink_inactive() to fix the following GCC warning when
> > building with 'W=1':
> >
> >   kernel/bpf/bpf_lru_list.c:216:41: warning: variable ‘first_node’ set but not used [-Wunused-but-set-variable]
> >
> > Cc: Martin KaFai Lau <kafai@...com>
> > Signed-off-by: Tobias Klauser <tklauser@...tanz.ch>
> > ---
> >  kernel/bpf/bpf_lru_list.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/bpf_lru_list.c b/kernel/bpf/bpf_lru_list.c
> > index 89b7ef41c86b..d78501ee0609 100644
> > --- a/kernel/bpf/bpf_lru_list.c
> > +++ b/kernel/bpf/bpf_lru_list.c
> > @@ -213,11 +213,10 @@ __bpf_lru_list_shrink_inactive(struct bpf_lru *lru,
> >  			       enum bpf_lru_list_type tgt_free_type)
> >  {
> >  	struct list_head *inactive = &l->lists[BPF_LRU_LIST_T_INACTIVE];
> > -	struct bpf_lru_node *node, *tmp_node, *first_node;
> > +	struct bpf_lru_node *node, *tmp_node;
> >  	unsigned int nshrinked = 0;
> >  	unsigned int i = 0;
> >
> > -	first_node = list_first_entry(inactive, struct bpf_lru_node, list);
> >  	list_for_each_entry_safe_reverse(node, tmp_node, inactive, list) {
> >  		if (bpf_lru_node_is_ref(node)) {
> >  			__bpf_lru_node_move(l, node, BPF_LRU_LIST_T_ACTIVE);
>
> Martin,
> I cannot tell whether it's actually copy-paste leftover
> or this patch is needed:
I made some changes to __bpf_lru_list_shrink_inactive() which made
first_node checking unnecessary but I did not remove first_node all
together by mistake.

__bpf_lru_list_rotate_active() pushes node back to the head, so we
need to remember the original first_node and break accordingly.

__bpf_lru_list_shrink_inactive() does not do that, so there is no
need to test against first_node.