Commit 38ec4944b5 ("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: 38ec4944b5 ("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>
7ad18ff644