From: Neil Horman Date: Thu, 16 Feb 2012 01:48:56 +0000 (+0000) Subject: vmxnet3: cap copy length at size of skb to prevent dropped frames on tx X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=b203262de63c56393d09e254242b57c002d8619d;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git vmxnet3: cap copy length at size of skb to prevent dropped frames on tx I was recently shown that vmxnet3 devices on transmit, will drop very small udp frames consistently. This is due to a regression introduced by commit 39d4a96fd7d2926e46151adbd18b810aeeea8ec0. This commit attempts to introduce an optimization to the tx path, indicating that the underlying hardware behaves optimally when at least 54 bytes of header data are available for direct access. This causes problems however, if the entire frame is less than 54 bytes long. The subsequent pskb_may_pull in vmxnet3_parse_and_copy_hdr fails, causing an error return code, which leads to vmxnet3_tq_xmit dropping the frame. Fix it by placing a cap on the copy length. For frames longer than 54 bytes, we do the pull as we normally would. If the frame is shorter than that, copy the whole frame, but no more. This ensures that we still get the optimization for qualifying frames, but don't do any damange for frames that are too short. Also, since I'm unable to do this, it wuold be great if vmware could follow up this patch with some additional code commentary as to why 54 bytes is an optimal pull length for a virtual NIC driver. The comment that introduced this was vague on that. Thanks! Signed-off-by: Neil Horman Reported-by: Max Matveev CC: Max Matveev CC: "David S. Miller" CC: Shreyas Bhatewara CC: "VMware, Inc." Signed-off-by: Shreyas N Bhatewara Signed-off-by: David S. Miller --- diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c index de7fc345148a..3dcd3857a36c 100644 --- a/drivers/net/vmxnet3/vmxnet3_drv.c +++ b/drivers/net/vmxnet3/vmxnet3_drv.c @@ -843,8 +843,8 @@ vmxnet3_parse_and_copy_hdr(struct sk_buff *skb, struct vmxnet3_tx_queue *tq, /* for simplicity, don't copy L4 headers */ ctx->l4_hdr_size = 0; } - ctx->copy_size = ctx->eth_ip_hdr_size + - ctx->l4_hdr_size; + ctx->copy_size = min(ctx->eth_ip_hdr_size + + ctx->l4_hdr_size, skb->len); } else { ctx->eth_ip_hdr_size = 0; ctx->l4_hdr_size = 0;