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Date: Tue, 20 Nov 2012 15:44:50 +0000 From: "Jan Beulich" <JBeulich@...e.com> To: "Ian Campbell" <Ian.Campbell@...rix.com> Cc: "Stefan Bader" <stefan.bader@...onical.com>, "Sander Eikelenboom" <linux@...elenboom.it>, "Eric Dumazet" <edumazet@...gle.com>, "KonradRzeszutekWilk" <konrad@...nel.org>, "xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>, "ANNIE LI" <annie.li@...cle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: [Xen-devel] [PATCH] xen/netfront: handle compound page fragments on transmit >>> On 20.11.12 at 16:06, Ian Campbell <Ian.Campbell@...rix.com> wrote: > On Tue, 2012-11-20 at 14:32 +0000, Jan Beulich wrote: >> > @@ -517,15 +540,16 @@ static int xennet_start_xmit(struct sk_buff *skb, >> > struct net_device *dev) >> > grant_ref_t ref; >> > unsigned long mfn; >> > int notify; >> > - int frags = skb_shinfo(skb)->nr_frags; >> > + int slots; >> > unsigned int offset = offset_in_page(data); >> > unsigned int len = skb_headlen(skb); >> > unsigned long flags; >> > >> > - frags += DIV_ROUND_UP(offset + len, PAGE_SIZE); >> > - if (unlikely(frags > MAX_SKB_FRAGS + 1)) { >> > - printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n", >> > - frags); >> > + slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) + >> > + xennet_count_skb_frag_slots(skb); >> > + if (unlikely(slots > MAX_SKB_FRAGS + 1)) { >> >> But still - isn't this wrong now (i.e. can't it now validly exceed the >> boundary checked for)? > > In practice no because of the property that the number of pages backing > the frags is <= MAX_SKB_FRAGS even if you are using compound pages as > the frags. So are you saying that there is something in the system preventing up to MAX_SKB_FRAGS * SKB_FRAG_PAGE_ORDER (or NETDEV_FRAG_PAGE_MAX_ORDER) skb-s to be created? I didn't find any. I do notice that __netdev_alloc_frag() currently never gets called with a size larger than PAGE_SIZE, but considering that the function just recently got made capable of that, I'm sure respective users will show up rather sooner than later. Jan -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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