flow_dissector: work around stack frame size warning (0af413bd) · Commits · 戴 / test

The fl_flow_key structure is around 500 bytes, so having two of them on the stack in one function now exceeds the warning limit after an otherwise correct change: net/sched/cls_flower.c:298:12: error: stack frame size of 1056 bytes in function 'fl_classify' [-Werror,-Wframe-larger-than=] I suspect the fl_classify function could be reworked to only have one of them on the stack and modify it in place, but I could not work out how to do that. As a somewhat hacky workaround, move one of them into an out-of-line function to reduce its scope. This does not necessarily reduce the stack usage of the outer function, but at least the second copy is removed from the stack during most of it and does not add up to whatever is called from there. I now see 552 bytes of stack usage for fl_classify(), plus 528 bytes for fl_mask_lookup(). Fixes: ("flow_dissector: Parse multiple MPLS Label Stack Entries") Signed-off-by:

Arnd Bergmann <arnd@arndb.de> Acked-by:

Cong Wang <xiyou.wangcong@gmail.com> Acked-by:

Guillaume Nault <gnault@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

+8 −9

Original line number	Diff line number	Diff line
		@@ -272,14 +272,16 @@ static struct cls_fl_filter fl_lookup_range(struct fl_flow_mask mask,
		return NULL;
		}

		static struct cls_fl_filter fl_lookup(struct fl_flow_mask mask,
		struct fl_flow_key *mkey,
		struct fl_flow_key *key)
		static noinline_for_stack
		struct cls_fl_filter fl_mask_lookup(struct fl_flow_mask mask, struct fl_flow_key *key)
		{
		struct fl_flow_key mkey;

		fl_set_masked_key(&mkey, key, mask);
		if ((mask->flags & TCA_FLOWER_MASK_FLAGS_RANGE))
		return fl_lookup_range(mask, mkey, key);
		return fl_lookup_range(mask, &mkey, key);

		return __fl_lookup(mask, mkey);
		return __fl_lookup(mask, &mkey);
		}

		static u16 fl_ct_info_to_flower_map[] = {
		@@ -299,7 +301,6 @@ static int fl_classify(struct sk_buff skb, const struct tcf_proto tp,
		struct tcf_result *res)
		{
		struct cls_fl_head *head = rcu_dereference_bh(tp->root);
		struct fl_flow_key skb_mkey;
		struct fl_flow_key skb_key;
		struct fl_flow_mask *mask;
		struct cls_fl_filter *f;
		@@ -319,9 +320,7 @@ static int fl_classify(struct sk_buff skb, const struct tcf_proto tp,
		ARRAY_SIZE(fl_ct_info_to_flower_map));
		skb_flow_dissect(skb, &mask->dissector, &skb_key, 0);

		fl_set_masked_key(&skb_mkey, &skb_key, mask);

		f = fl_lookup(mask, &skb_mkey, &skb_key);
		f = fl_mask_lookup(mask, &skb_key);
		if (f && !tc_skip_sw(f->flags)) {
		*res = f->res;
		return tcf_exts_exec(skb, &f->exts, res);

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