From: t_jeang <devnull@localhost>
Date: Tue, 6 Jan 2009 12:06:02 +0000 (+0000)
Subject: imported patch netback-defensive.patch
X-Git-Tag: netback-linearise-skbs
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=0e7608495197e2bcaf317b225c9cc4dc9b008ca3;p=xenclient%2Fkernel.git

imported patch netback-defensive.patch
---

diff --git a/drivers/xen/netback/netback.c b/drivers/xen/netback/netback.c
index c853fd40..c91849d9 100644
--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -89,15 +89,17 @@ static inline unsigned long idx_to_kaddr(unsigned int idx)
 	return (unsigned long)pfn_to_kaddr(idx_to_pfn(idx));
 }
 
-/* extra field used in struct page */
+/* we use an extra field in struct page to map pages to pending reqs */
+#define NETIF_INDEX_MASK 0xABCD0000UL    /* magic sanity check value */
 static inline void netif_set_page_index(struct page *pg, unsigned int index)
 {
-	*(unsigned long *)&pg->mapping = index;
+	*(unsigned long *)&pg->mapping = index | NETIF_INDEX_MASK;
 }
 
 static inline int netif_page_index(struct page *pg)
 {
-	unsigned long idx = (unsigned long)pg->mapping;
+	unsigned long val = (unsigned long)pg->mapping;
+	unsigned long idx = val & ~NETIF_INDEX_MASK;
 
 	if (!PageForeign(pg))
 		return -1;
@@ -105,6 +107,19 @@ static inline int netif_page_index(struct page *pg)
 	if ((idx >= MAX_PENDING_REQS) || (mmap_pages[idx] != pg))
 		return -1;
 
+	if (unlikely((val & NETIF_INDEX_MASK) != NETIF_INDEX_MASK)) {
+		printk(KERN_ERR "apparent netback page %p doesn't have NETIF_INDEX_MASK magic: %lx, dtor %#lx\n",
+		       pg, val, pg->index);
+		printk(KERN_ERR "-- page flags are %lx - %s; %s; %s\n",
+		       pg->flags,
+		       PageForeign(pg) ? "FOREIGN" : "not-foreign",
+		       PageNetback(pg) ? "NETBACK" : "not-netback",
+		       PageBlkback(pg) ? "BLKBACK" : "not-blkback");
+		printk(KERN_ERR "-- page flags are %lx\n", pg->flags);
+		printk(KERN_ERR "-- page count is %d\n", page_count(pg));
+		BUG();
+	}
+
 	return idx;
 }