| Message ID | 1418232388-16853-1-git-send-email-luis.henriques@canonical.com |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, Dec 10, 2014 at 05:26:28PM +0000, Luis Henriques wrote: > This is a note to let you know that I have just added a patch titled > > xen-netfront: Fix handling packets on compound pages with skb_linearize > > to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree > which can be found at: > > http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue > > This patch is scheduled to be released in version 3.16.7-ckt3. > > If you, or anyone else, feels it should not be added to this tree, please > reply to this email. > Ups, sorry! I thought I had this one dropped after David Vrabel comment. Now dropped for sure. Cheers, -- Luís > For more information about the 3.16.y-ckt tree, see > https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable > > Thanks. > -Luis > > ------ > > From 079f869ca5082866d276b686721e89a649e622fe Mon Sep 17 00:00:00 2001 > From: Zoltan Kiss <zoltan.kiss@citrix.com> > Date: Mon, 11 Aug 2014 18:32:23 +0100 > Subject: xen-netfront: Fix handling packets on compound pages with > skb_linearize > > commit 97a6d1bb2b658ac85ed88205ccd1ab809899884d upstream. > > There is a long known problem with the netfront/netback interface: if the guest > tries to send a packet which constitues more than MAX_SKB_FRAGS + 1 ring slots, > it gets dropped. The reason is that netback maps these slots to a frag in the > frags array, which is limited by size. Having so many slots can occur since > compound pages were introduced, as the ring protocol slice them up into > individual (non-compound) page aligned slots. The theoretical worst case > scenario looks like this (note, skbs are limited to 64 Kb here): > linear buffer: at most PAGE_SIZE - 17 * 2 bytes, overlapping page boundary, > using 2 slots > first 15 frags: 1 + PAGE_SIZE + 1 bytes long, first and last bytes are at the > end and the beginning of a page, therefore they use 3 * 15 = 45 slots > last 2 frags: 1 + 1 bytes, overlapping page boundary, 2 * 2 = 4 slots > Although I don't think this 51 slots skb can really happen, we need a solution > which can deal with every scenario. In real life there is only a few slots > overdue, but usually it causes the TCP stream to be blocked, as the retry will > most likely have the same buffer layout. > This patch solves this problem by linearizing the packet. This is not the > fastest way, and it can fail much easier as it tries to allocate a big linear > area for the whole packet, but probably easier by an order of magnitude than > anything else. Probably this code path is not touched very frequently anyway. > > Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com> > Cc: Wei Liu <wei.liu2@citrix.com> > Cc: Ian Campbell <Ian.Campbell@citrix.com> > Cc: Paul Durrant <paul.durrant@citrix.com> > Cc: netdev@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: xen-devel@lists.xenproject.org > Signed-off-by: David S. Miller <davem@davemloft.net> > Cc: Stefan Bader <stefan.bader@canonical.com> > Signed-off-by: Luis Henriques <luis.henriques@canonical.com> > --- > drivers/net/xen-netfront.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c > index 055222bae6e4..23359aeb1ba0 100644 > --- a/drivers/net/xen-netfront.c > +++ b/drivers/net/xen-netfront.c > @@ -628,9 +628,10 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev) > slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) + > xennet_count_skb_frag_slots(skb); > if (unlikely(slots > MAX_SKB_FRAGS + 1)) { > - net_alert_ratelimited( > - "xennet: skb rides the rocket: %d slots\n", slots); > - goto drop; > + net_dbg_ratelimited("xennet: skb rides the rocket: %d slots, %d bytes\n", > + slots, skb->len); > + if (skb_linearize(skb)) > + goto drop; > } > > spin_lock_irqsave(&queue->tx_lock, flags); -- 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
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index 055222bae6e4..23359aeb1ba0 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -628,9 +628,10 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev) slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) + xennet_count_skb_frag_slots(skb); if (unlikely(slots > MAX_SKB_FRAGS + 1)) { - net_alert_ratelimited( - "xennet: skb rides the rocket: %d slots\n", slots); - goto drop; + net_dbg_ratelimited("xennet: skb rides the rocket: %d slots, %d bytes\n", + slots, skb->len); + if (skb_linearize(skb)) + goto drop; } spin_lock_irqsave(&queue->tx_lock, flags);
This is a note to let you know that I have just added a patch titled xen-netfront: Fix handling packets on compound pages with skb_linearize to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt3. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 079f869ca5082866d276b686721e89a649e622fe Mon Sep 17 00:00:00 2001 From: Zoltan Kiss <zoltan.kiss@citrix.com> Date: Mon, 11 Aug 2014 18:32:23 +0100 Subject: xen-netfront: Fix handling packets on compound pages with skb_linearize commit 97a6d1bb2b658ac85ed88205ccd1ab809899884d upstream. There is a long known problem with the netfront/netback interface: if the guest tries to send a packet which constitues more than MAX_SKB_FRAGS + 1 ring slots, it gets dropped. The reason is that netback maps these slots to a frag in the frags array, which is limited by size. Having so many slots can occur since compound pages were introduced, as the ring protocol slice them up into individual (non-compound) page aligned slots. The theoretical worst case scenario looks like this (note, skbs are limited to 64 Kb here): linear buffer: at most PAGE_SIZE - 17 * 2 bytes, overlapping page boundary, using 2 slots first 15 frags: 1 + PAGE_SIZE + 1 bytes long, first and last bytes are at the end and the beginning of a page, therefore they use 3 * 15 = 45 slots last 2 frags: 1 + 1 bytes, overlapping page boundary, 2 * 2 = 4 slots Although I don't think this 51 slots skb can really happen, we need a solution which can deal with every scenario. In real life there is only a few slots overdue, but usually it causes the TCP stream to be blocked, as the retry will most likely have the same buffer layout. This patch solves this problem by linearizing the packet. This is not the fastest way, and it can fail much easier as it tries to allocate a big linear area for the whole packet, but probably easier by an order of magnitude than anything else. Probably this code path is not touched very frequently anyway. Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com> Cc: Wei Liu <wei.liu2@citrix.com> Cc: Ian Campbell <Ian.Campbell@citrix.com> Cc: Paul Durrant <paul.durrant@citrix.com> Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: xen-devel@lists.xenproject.org Signed-off-by: David S. Miller <davem@davemloft.net> Cc: Stefan Bader <stefan.bader@canonical.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/net/xen-netfront.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 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