| Message ID | 51E65F5102000078000E57ED@nat28.tlf.novell.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2013-07-17 at 08:09 +0100, Jan Beulich wrote: > Due to commit 3683243b ("xen-netfront: use __pskb_pull_tail to ensure > linear area is big enough on RX") xennet_fill_frags() may end up > filling MAX_SKB_FRAGS + 1 fragments in a receive skb, and only reduce > the fragment count subsequently via __pskb_pull_tail(). That's a > result of xennet_get_responses() allowing a maximum of one more slot to > be consumed (and intermediately transformed into a fragment) if the > head slot has a size less than or equal to RX_COPY_THRESHOLD. > > Hence we need to adjust xennet_fill_frags() to pull earlier if we > reached the maximum fragment count - due to the described behavior of > xennet_get_responses() this guarantees that at least the first fragment > will get completely consumed, and hence the fragment count reduced. > > In order to not needlessly call __pskb_pull_tail() twice, make the > original call conditional upon the pull target not having been reached > yet, and defer the newly added one as much as possible (an alternative > would have been to always call the function right before the call to > xennet_fill_frags(), but that would imply more frequent cases of > needing to call it twice). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > Acked-by: Wei Liu <wei.liu2@citrix.com> Acked-by: Ian Campbell <ian.campbell@citrix.com> Ian. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Ian Campbell <Ian.Campbell@citrix.com> Date: Wed, 17 Jul 2013 09:26:24 +0100 > On Wed, 2013-07-17 at 08:09 +0100, Jan Beulich wrote: >> Due to commit 3683243b ("xen-netfront: use __pskb_pull_tail to ensure >> linear area is big enough on RX") xennet_fill_frags() may end up >> filling MAX_SKB_FRAGS + 1 fragments in a receive skb, and only reduce >> the fragment count subsequently via __pskb_pull_tail(). That's a >> result of xennet_get_responses() allowing a maximum of one more slot to >> be consumed (and intermediately transformed into a fragment) if the >> head slot has a size less than or equal to RX_COPY_THRESHOLD. >> >> Hence we need to adjust xennet_fill_frags() to pull earlier if we >> reached the maximum fragment count - due to the described behavior of >> xennet_get_responses() this guarantees that at least the first fragment >> will get completely consumed, and hence the fragment count reduced. >> >> In order to not needlessly call __pskb_pull_tail() twice, make the >> original call conditional upon the pull target not having been reached >> yet, and defer the newly added one as much as possible (an alternative >> would have been to always call the function right before the call to >> xennet_fill_frags(), but that would imply more frequent cases of >> needing to call it twice). >> >> Signed-off-by: Jan Beulich <jbeulich@suse.com> >> Acked-by: Wei Liu <wei.liu2@citrix.com> > > Acked-by: Ian Campbell <ian.campbell@citrix.com> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- 3.11-rc1/drivers/net/xen-netfront.c +++ 3.11-rc1-xen-netfront-pull-earlier/drivers/net/xen-netfront.c @@ -286,8 +286,7 @@ no_skb: break; } - __skb_fill_page_desc(skb, 0, page, 0, 0); - skb_shinfo(skb)->nr_frags = 1; + skb_add_rx_frag(skb, 0, page, 0, 0, PAGE_SIZE); __skb_queue_tail(&np->rx_batch, skb); } @@ -831,7 +830,6 @@ static RING_IDX xennet_fill_frags(struct struct sk_buff_head *list) { struct skb_shared_info *shinfo = skb_shinfo(skb); - int nr_frags = shinfo->nr_frags; RING_IDX cons = np->rx.rsp_cons; struct sk_buff *nskb; @@ -840,19 +838,21 @@ static RING_IDX xennet_fill_frags(struct RING_GET_RESPONSE(&np->rx, ++cons); skb_frag_t *nfrag = &skb_shinfo(nskb)->frags[0]; - __skb_fill_page_desc(skb, nr_frags, - skb_frag_page(nfrag), - rx->offset, rx->status); + if (shinfo->nr_frags == MAX_SKB_FRAGS) { + unsigned int pull_to = NETFRONT_SKB_CB(skb)->pull_to; - skb->data_len += rx->status; + BUG_ON(pull_to <= skb_headlen(skb)); + __pskb_pull_tail(skb, pull_to - skb_headlen(skb)); + } + BUG_ON(shinfo->nr_frags >= MAX_SKB_FRAGS); + + skb_add_rx_frag(skb, shinfo->nr_frags, skb_frag_page(nfrag), + rx->offset, rx->status, PAGE_SIZE); skb_shinfo(nskb)->nr_frags = 0; kfree_skb(nskb); - - nr_frags++; } - shinfo->nr_frags = nr_frags; return cons; } @@ -933,7 +933,8 @@ static int handle_incoming_queue(struct while ((skb = __skb_dequeue(rxq)) != NULL) { int pull_to = NETFRONT_SKB_CB(skb)->pull_to; - __pskb_pull_tail(skb, pull_to - skb_headlen(skb)); + if (pull_to > skb_headlen(skb)) + __pskb_pull_tail(skb, pull_to - skb_headlen(skb)); /* Ethernet work: Delayed to here as it peeks the header. */ skb->protocol = eth_type_trans(skb, dev); @@ -1019,16 +1020,10 @@ err: skb_shinfo(skb)->frags[0].page_offset = rx->offset; skb_frag_size_set(&skb_shinfo(skb)->frags[0], rx->status); skb->data_len = rx->status; + skb->len += rx->status; i = xennet_fill_frags(np, skb, &tmpq); - /* - * Truesize is the actual allocation size, even if the - * allocation is only partially used. - */ - skb->truesize += PAGE_SIZE * skb_shinfo(skb)->nr_frags; - skb->len += skb->data_len; - if (rx->flags & XEN_NETRXF_csum_blank) skb->ip_summed = CHECKSUM_PARTIAL; else if (rx->flags & XEN_NETRXF_data_validated)
Due to commit 3683243b ("xen-netfront: use __pskb_pull_tail to ensure linear area is big enough on RX") xennet_fill_frags() may end up filling MAX_SKB_FRAGS + 1 fragments in a receive skb, and only reduce the fragment count subsequently via __pskb_pull_tail(). That's a result of xennet_get_responses() allowing a maximum of one more slot to be consumed (and intermediately transformed into a fragment) if the head slot has a size less than or equal to RX_COPY_THRESHOLD. Hence we need to adjust xennet_fill_frags() to pull earlier if we reached the maximum fragment count - due to the described behavior of xennet_get_responses() this guarantees that at least the first fragment will get completely consumed, and hence the fragment count reduced. In order to not needlessly call __pskb_pull_tail() twice, make the original call conditional upon the pull target not having been reached yet, and defer the newly added one as much as possible (an alternative would have been to always call the function right before the call to xennet_fill_frags(), but that would imply more frequent cases of needing to call it twice). Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Wei Liu <wei.liu2@citrix.com> Cc: Ian Campbell <ian.campbell@citrix.com> Cc: stable@vger.kernel.org (3.6 onwards) --- v3: Break up a "complex" assignment into two simple ones. v2: Use skb_add_rx_frag() to keep all accounting fields up to date as we go (skb->len needing intermediate updating was pointed out by Wei Liu and David Miller, shinfo->nr_frags needing updating before calling __pskb_pull_tail() was spotted out by Dion Kant). --- drivers/net/xen-netfront.c | 31 +++++++++++++------------------ 1 file changed, 13 insertions(+), 18 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html