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Date: Tue, 9 Jul 2013 17:16:13 +0100
From: Wei Liu <wei.liu2@...rix.com>
To: Annie Li <annie.li@...cle.com>
CC: <xen-devel@...ts.xensource.com>, <netdev@...r.kernel.org>,
<Ian.Campbell@...rix.com>, <konrad.wilk@...cle.com>,
<wei.liu2@...rix.com>
Subject: Re: [PATCH 1/1] xen/netback: correctly calculate required slots of
skb.
On Tue, Jul 09, 2013 at 02:15:20PM +0800, Annie Li wrote:
> When counting required slots for skb, netback directly uses DIV_ROUND_UP to get
> slots required by header data. This is wrong when offset in the page of header
> data is not zero, and is also inconsistent with following calculation for
> required slot in netbk_gop_skb.
>
> In netbk_gop_skb, required slots are calculated based on offset and len in page
> of header data. It is possible that required slots here is larger than the one
> calculated in earlier netbk_count_requests. This inconsistency directly results
> in rx_req_cons_peek and xen_netbk_rx_ring_full judgement are wrong.
>
> Then it comes to situation the ring is actually full, but netback thinks it is
> not and continues to create responses. This results in response overlaps request
> in the ring, then grantcopy gets wrong grant reference and throws out error,
> for example "(XEN) grant_table.c:1763:d0 Bad grant reference 2949120", the
> grant reference is invalid value here. Netback returns XEN_NETIF_RSP_ERROR(-1)
> to netfront when grant copy status is error, then netfront gets rx->status
> (the status is -1, not really data size now), and throws out error,
> "kernel: net eth1: rx->offset: 0, size: 4294967295". This issue can be reproduced
> by doing gzip/gunzip in nfs share with mtu = 9000, the guest would panic after
> running such test for a while.
>
> This patch is based on 3.10-rc7.
>
> Signed-off-by: Annie Li <annie.li@...cle.com>
> ---
> drivers/net/xen-netback/netback.c | 97 +++++++++++++++++++++++++-----------
> 1 files changed, 67 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 8c20935..7ff9333 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -359,51 +359,88 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> * the guest. This function is essentially a dry run of
> * netbk_gop_frag_copy.
> */
Just to be clear, now the above comment applies to your new function,
right?
> -unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
> +static void netbk_get_slots(struct xenvif *vif, struct sk_buff *skb,
A better name would be netbk_count_slots because it doesn't actually
acquire any slots.
And you can make it return the slot count and adds that to the total
number of slots in the caller, as this function doesn't seem to rely on
previous count so there is not much point passing in *count.
> + struct page *page, int *copy_off,
> + unsigned long size, unsigned long offset,
> + int *head, int *count)
> {
> - unsigned int count;
> - int i, copy_off;
> + unsigned long bytes;
>
> - count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE);
> + /* Data must not cross a page boundary. */
> + BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>
> - copy_off = skb_headlen(skb) % PAGE_SIZE;
> + /* Skip unused frames from start of page */
> + page += offset >> PAGE_SHIFT;
> + offset &= ~PAGE_MASK;
>
> - if (skb_shinfo(skb)->gso_size)
> - count++;
> + while (size > 0) {
> + BUG_ON(offset >= PAGE_SIZE);
> + BUG_ON(*copy_off > MAX_BUFFER_OFFSET);
>
> - for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> - unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
> - unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;
> - unsigned long bytes;
> + bytes = PAGE_SIZE - offset;
>
> - offset &= ~PAGE_MASK;
> + if (bytes > size)
> + bytes = size;
>
> - while (size > 0) {
> - BUG_ON(offset >= PAGE_SIZE);
> - BUG_ON(copy_off > MAX_BUFFER_OFFSET);
> + if (start_new_rx_buffer(*copy_off, bytes, *head)) {
> + *count = *count + 1;
> + *copy_off = 0;
> + }
>
> - bytes = PAGE_SIZE - offset;
> + if (*copy_off + bytes > MAX_BUFFER_OFFSET)
> + bytes = MAX_BUFFER_OFFSET - *copy_off;
>
> - if (bytes > size)
> - bytes = size;
> + *copy_off += bytes;
>
> - if (start_new_rx_buffer(copy_off, bytes, 0)) {
> - count++;
> - copy_off = 0;
> - }
> + offset += bytes;
> + size -= bytes;
>
> - if (copy_off + bytes > MAX_BUFFER_OFFSET)
> - bytes = MAX_BUFFER_OFFSET - copy_off;
> + /* Next frame */
> + if (offset == PAGE_SIZE && size) {
> + BUG_ON(!PageCompound(page));
> + page++;
> + offset = 0;
> + }
>
> - copy_off += bytes;
> + if (*head)
This seems to differ from netbk_gop_frag_copy. In that function it's
like
if (*head && skb_shinfo(skb)->gso_size && !vif->gso_prefix)
Wei.
> + *count = *count + 1;
> + *head = 0; /* There must be something in this buffer now. */
> + }
> +}
> +
> +unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
> +{
> + int i, copy_off = 0;
> + int nr_frags = skb_shinfo(skb)->nr_frags;
> + unsigned char *data;
> + int head = 1;
> + unsigned int count = 0;
>
> - offset += bytes;
> - size -= bytes;
> + if (skb_shinfo(skb)->gso_size)
> + count++;
>
> - if (offset == PAGE_SIZE)
> - offset = 0;
> - }
> + data = skb->data;
> + while (data < skb_tail_pointer(skb)) {
> + unsigned int offset = offset_in_page(data);
> + unsigned int len = PAGE_SIZE - offset;
> +
> + if (data + len > skb_tail_pointer(skb))
> + len = skb_tail_pointer(skb) - data;
> +
> + netbk_get_slots(vif, skb, virt_to_page(data), ©_off,
> + len, offset, &head, &count);
> + data += len;
> + }
> +
> + for (i = 0; i < nr_frags; i++) {
> + netbk_get_slots(vif, skb,
> + skb_frag_page(&skb_shinfo(skb)->frags[i]),
> + ©_off,
> + skb_frag_size(&skb_shinfo(skb)->frags[i]),
> + skb_shinfo(skb)->frags[i].page_offset,
> + &head, &count);
> }
> +
> return count;
> }
>
> --
> 1.7.3.4
>
> --
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