Re: [PATCH] tcp: splice as many packets as possible at once

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To: <herbert@...>
Cc: <zbr@...>, <dada1@...>, <w@...>, <ben@...>, <jarkao2@...>, <mingo@...>, <linux-kernel@...>, <netdev@...>, <jens.axboe@...>
Date: Wednesday, January 14, 2009 - 3:27 am

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Wed, 14 Jan 2009 14:51:24 +1100


So while trying to figure out a sane way to fix this, I found
another bug:

	/*
	 * map the linear part
	 */
	if (__splice_segment(virt_to_page(skb->data),
			     (unsigned long) skb->data & (PAGE_SIZE - 1),
			     skb_headlen(skb),
			     offset, len, skb, spd))
		return 1;

This will explode if the SLAB cache for skb->head is using compound
(ie. order > 0) pages.

For example, if this is an order-1 page being used for the skb->head
data (which would be true on most systems for jumbo MTU frames being
received into a linear SKB), the offset will be wrong and depending
upon skb_headlen() we could reference past the end of that
non-compound page we will end up grabbing a reference to.

And then we'll end up with a compound page in an skb_shinfo() frag
array, which is illegal.

Well, at least, I can list several drivers that will barf when
trying to TX that (Acenic, atlx1, cassini, jme, sungem), since
they use pci_map_page(... virt_to_page(skb->data)) or similar.

The core KMAP'ing support for SKBs will also not be able to grok
such a beastly SKB.

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Messages in current thread:
[PATCH] tcp: splice as many packets as possible at once, Willy Tarreau, (Thu Jan 8, 1:30 pm)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Fri Jan 9, 6:42 pm)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Sun Jan 11, 8:58 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Sun Jan 11, 9:35 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Sun Jan 11, 12:05 pm)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Tue Jan 13, 8:13 pm)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Tue Jan 13, 8:22 pm)
Re: [PATCH] tcp: splice as many packets as possible at once, David Miller, (Wed Jan 14, 3:27 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 4:53 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Tue Jan 20, 4:37 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Fri Jan 16, 2:51 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Tue Jan 20, 8:11 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Tue Jan 20, 10:06 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Mon Jan 19, 4:40 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Mon Jan 26, 3:59 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 5:54 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 8:15 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 8:06 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 5:42 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 6:47 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 7:40 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Jarek Poplawski, (Wed Jan 14, 7:45 am)
Re: [PATCH] tcp: splice as many packets as possible at once, Evgeniy Polyakov, (Fri Jan 9, 7:01 pm)
[PATCH] tcp: splice as many packets as possible at once, Willy Tarreau, (Thu Jan 8, 4:16 pm)