From: Wolfram Joost <dbox2@frokaschwei.de>
Subject: [PATCH] fork_cacheflush

On ASUS WL-500gP there are many unexpected "Segmentation fault"s that
seem to be caused by a kernel. They can be avoided by:
1) Disabling highpage
2) Using flush_cache_mm in flush_cache_dup_mm

For details see OpenWrt ticket #2035 https://dev.openwrt.org/ticket/2035
---
--- a/arch/mips/include/asm/cacheflush.h
+++ b/arch/mips/include/asm/cacheflush.h
@@ -46,7 +46,7 @@
 extern void (*flush_cache_all)(void);
 extern void (*__flush_cache_all)(void);
 extern void (*flush_cache_mm)(struct mm_struct *mm);
-#define flush_cache_dup_mm(mm)	do { (void) (mm); } while (0)
+#define flush_cache_dup_mm(mm) flush_cache_mm(mm)
 extern void (*flush_cache_range)(struct vm_area_struct *vma,
 	unsigned long start, unsigned long end);
 extern void (*flush_cache_page)(struct vm_area_struct *vma, unsigned long page, unsigned long pfn);