[PATCH 2.6.27.2] datagram handling routines : mapping/unmapping paged data in soft IRQ

["Luc Goria" <Luc.Goria@adept-telecom.fr>]

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Kernel crashes when a network module tries to copy a datagram to iovec in soft IRQ with paged data.
The problem is that kunmap function can't be called in IRQ.
All calls to kmap/kunmap fonctions are replaced by calls to kmap_skb_frag/kunmap_skb_frag when paged data are involved.

 <<datagram.c.patch>> 
Signed-off-by: Luc GORIA <luc.goria@adept-telecom.fr>

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--- linux-2.6.27.2/net/core/datagram.c	2009-05-06 17:43:08.000000000 +0200
+++ my-linux-2.6.27.2/net/core/datagram.c	2009-05-06 17:52:44.000000000 +0200
@@ -56,6 +56,8 @@
 #include <net/sock.h>
 #include <net/tcp_states.h>
 
+#include "kmap_skb.h"
+
 /*
  *	Is a socket 'connection oriented' ?
  */
@@ -292,14 +294,13 @@
 			int err;
 			u8  *vaddr;
 			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
-			struct page *page = frag->page;
 
 			if (copy > len)
 				copy = len;
-			vaddr = kmap(page);
+			vaddr = kmap_skb_frag(frag);
 			err = memcpy_toiovec(to, vaddr + frag->page_offset +
 					     offset - start, copy);
-			kunmap(page);
+			kunmap_skb_frag(vaddr);
 			if (err)
 				goto fault;
 			if (!(len -= copy))
@@ -377,14 +378,13 @@
 			int err;
 			u8  *vaddr;
 			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
-			struct page *page = frag->page;
 
 			if (copy > len)
 				copy = len;
-			vaddr = kmap(page);
+			vaddr = kmap_skb_frag(frag);
 			err = memcpy_fromiovec(vaddr + frag->page_offset +
 					       offset - start, from, copy);
-			kunmap(page);
+			kunmap_skb_frag(vaddr);
 			if (err)
 				goto fault;
 
@@ -461,16 +461,15 @@
 			int err = 0;
 			u8  *vaddr;
 			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
-			struct page *page = frag->page;
 
 			if (copy > len)
 				copy = len;
-			vaddr = kmap(page);
+			vaddr = kmap_skb_frag(frag);
 			csum2 = csum_and_copy_to_user(vaddr +
 							frag->page_offset +
 							offset - start,
 						      to, copy, 0, &err);
-			kunmap(page);
+			kunmap_skb_frag(vaddr);
 			if (err)
 				goto fault;
 			*csump = csum_block_add(*csump, csum2, pos);