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gro: fix napi_gro_frags() Fast GRO breakage due to IP alignment check

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[ Upstream commit 7ad18ff6449cbd6beb26b53128ddf56d2685aa93 ]

Commit 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
did the right thing, but missed the fact that napi_gro_frags() logics
calls for skb_gro_reset_offset() *before* pulling Ethernet header
to the skb linear space.
That said, the introduced check for frag0 address being aligned to 4
always fails for it as Ethernet header is obviously 14 bytes long,
and in case with NET_IP_ALIGN its start is not aligned to 4.

Fix this by adding @nhoff argument to skb_gro_reset_offset() which
tells if an IP header is placed right at the start of frag0 or not.
This restores Fast GRO for napi_gro_frags() that became very slow
after the mentioned commit, and preserves the introduced check to
avoid silent unaligned accesses.

From v1 [0]:
 - inline tiny skb_gro_reset_offset() to let the code be optimized
   more efficively (esp. for the !NET_IP_ALIGN case) (Eric);
 - pull in Reviewed-by from Eric.

[0] https://lore.kernel.org/netdev/20210418114200.5839-1-alobakin@pm.me

Fixes: 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Alexander Lobakin 2021-04-19 12:53:06 +00:00 committed by Greg Kroah-Hartman
parent e97aea9f25
commit f7368865da
1 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
net/core/dev.c
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@ -5395,7 +5395,7 @@ static struct list_head *gro_list_prepare(struct napi_struct *napi,
return head;
}
static void skb_gro_reset_offset(struct sk_buff *skb)
static inline void skb_gro_reset_offset(struct sk_buff *skb, u32 nhoff)
{
const struct skb_shared_info *pinfo = skb_shinfo(skb);
const skb_frag_t *frag0 = &pinfo->frags[0];
@ -5407,7 +5407,7 @@ static void skb_gro_reset_offset(struct sk_buff *skb)
if (skb_mac_header(skb) == skb_tail_pointer(skb) &&
pinfo->nr_frags &&
!PageHighMem(skb_frag_page(frag0)) &&
(!NET_IP_ALIGN || !(skb_frag_off(frag0) & 3))) {
(!NET_IP_ALIGN || !((skb_frag_off(frag0) + nhoff) & 3))) {
NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
NAPI_GRO_CB(skb)->frag0_len = min_t(unsigned int,
skb_frag_size(frag0),
@ -5640,7 +5640,7 @@ gro_result_t napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
skb_mark_napi_id(skb, napi);
trace_napi_gro_receive_entry(skb);
skb_gro_reset_offset(skb);
skb_gro_reset_offset(skb, 0);
ret = napi_skb_finish(napi, skb, dev_gro_receive(napi, skb));
trace_napi_gro_receive_exit(ret);
@ -5733,7 +5733,7 @@ static struct sk_buff *napi_frags_skb(struct napi_struct *napi)
napi->skb = NULL;
skb_reset_mac_header(skb);
skb_gro_reset_offset(skb);
skb_gro_reset_offset(skb, hlen);
if (unlikely(skb_gro_header_hard(skb, hlen))) {
eth = skb_gro_header_slow(skb, hlen, 0);