netdev - Re: [PATCH] test_bpf: Add an skb_segment test for a non linear frag_list whose head_frag=1 and gso

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Date: Mon, 27 May 2024 21:59:45 +0800
From: Fred Li <dracodingfly@...il.com>
To: dracodingfly@...il.com
Cc: andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	davem@...emloft.net,
	john.fastabend@...il.com,
	kafai@...com,
	kpsingh@...nel.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	songliubraving@...com,
	yhs@...com
Subject: Re: [PATCH] test_bpf: Add an skb_segment test for a non linear frag_list whose head_frag=1 and gso_size was mangled

For kernel 6.6.8, when sg is true and skb_headlen(list_skb) != len, it also has 
chance run into this BUG_ON() line 4548.
'''
4544                 hsize = skb_headlen(head_skb) - offset;
4545 
4546                 if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
4547                     (skb_headlen(list_skb) == len || sg)) {
4548                         BUG_ON(skb_headlen(list_skb) > len);
4549 
4550                         nskb = skb_clone(list_skb, GFP_ATOMIC);
'''

As commit 9e4b7a99a03a("net: gso: fix panic on frag_list with mixed head alloc types")
said. It walk the frag_list in skb_segment and clear NETIF_F_SG when there is non head_frag 
skb. 

But for frag_list only with one head_frag, NETIF_F_SG was not cleared, if skb_headlen(list_skb) != len,
in this case, maybe we can fix it with run into segment as commit 13acc94eff122(net: permit skb_segment on 
head_frag frag_list skb). 

Any suggestions for resolving this issue.

Thanks

Fred Li