[PATCH] add a might_sleep() check to kmap()

kmap() can sleep, but rarely does.  Add a check for kmap() being called from
inappropriate contexts.

arch/i386/mm/highmem.c

@@ -2,8 +2,7 @@
 
 void *kmap(struct page *page)
 {
-	if (in_interrupt())
-		BUG();
+	might_sleep();
 	if (page < highmem_start_page)
 		return page_address(page);
 	return kmap_high(page);

include/linux/highmem.h

@@ -18,7 +18,11 @@ unsigned int nr_free_highpages(void);
 
 static inline unsigned int nr_free_highpages(void) { return 0; }
 
-static inline void *kmap(struct page *page) { return page_address(page); }
+static inline void *kmap(struct page *page)
+{
+	might_sleep();
+	return page_address(page);
+}
 
 #define kunmap(page) do { (void) (page); } while (0)