From cd9e2e5d3ff148be9ea210f622ce3e8e8292fcd6 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Mon, 16 May 2016 20:36:15 -0700 Subject: [PATCH] asix: Fix offset calculation in asix_rx_fixup() causing slow transmissions In testing with HiKey, we found that since commit 3f30b158eba5 ("asix: On RX avoid creating bad Ethernet frames"), we're seeing lots of noise during network transfers: [ 239.027993] asix 1-1.1:1.0 eth0: asix_rx_fixup() Data Header synchronisation was lost, remaining 988 [ 239.037310] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0x54ebb5ec, offset 4 [ 239.045519] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0xcdffe7a2, offset 4 [ 239.275044] asix 1-1.1:1.0 eth0: asix_rx_fixup() Data Header synchronisation was lost, remaining 988 [ 239.284355] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0x1d36f59d, offset 4 [ 239.292541] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0xaef3c1e9, offset 4 [ 239.518996] asix 1-1.1:1.0 eth0: asix_rx_fixup() Data Header synchronisation was lost, remaining 988 [ 239.528300] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0x2881912, offset 4 [ 239.536413] asix 1-1.1:1.0 eth0: asix_rx_fixup() Bad Header Length 0x5638f7e2, offset 4 And network throughput ends up being pretty bursty and slow with a overall throughput of at best ~30kB/s (where as previously we got 1.1MB/s with the slower USB1.1 "full speed" host). We found the issue also was reproducible on a x86_64 system, using a "high-speed" USB2.0 port but the throughput did not measurably drop (possibly due to the scp transfer being cpu bound on my slow test hardware). After lots of debugging, I found the check added in the problematic commit seems to be calculating the offset incorrectly. In the normal case, in the main loop of the function, we do: (where offset is zero, or set to "offset += (copy_length + 1) & 0xfffe" in the previous loop) rx->header = get_unaligned_le32(skb->data + offset); offset += sizeof(u32); But the problematic patch calculates: offset = ((rx->remaining + 1) & 0xfffe) + sizeof(u32); rx->header = get_unaligned_le32(skb->data + offset); Adding some debug logic to check those offset calculation used to find rx->header, the one in problematic code is always too large by sizeof(u32). Thus, this patch removes the incorrect " + sizeof(u32)" addition in the problematic calculation, and resolves the issue. Cc: Dean Jenkins Cc: "David B. Robins" Cc: Mark Craske Cc: Emil Goode Cc: "David S. Miller" Cc: YongQin Liu Cc: Guodong Xu Cc: Ivan Vecera Cc: linux-usb@vger.kernel.org Cc: netdev@vger.kernel.org Cc: stable #4.4+ Reported-by: Yongqin Liu Signed-off-by: John Stultz Signed-off-by: David S. Miller --- drivers/net/usb/asix_common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c index 0c5c22b84da8..7de5ab589e4e 100644 --- a/drivers/net/usb/asix_common.c +++ b/drivers/net/usb/asix_common.c @@ -66,7 +66,7 @@ int asix_rx_fixup_internal(struct usbnet *dev, struct sk_buff *skb, * buffer. */ if (rx->remaining && (rx->remaining + sizeof(u32) <= skb->len)) { - offset = ((rx->remaining + 1) & 0xfffe) + sizeof(u32); + offset = ((rx->remaining + 1) & 0xfffe); rx->header = get_unaligned_le32(skb->data + offset); offset = 0;