1 files changed, 37 insertions, 2 deletions

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index a48d7f11c7be..67918c22339c 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -1,8 +1,43 @@
 #ifndef __LINUX_UACCESS_H__
 #define __LINUX_UACCESS_H__
 
+#include <linux/preempt.h>
 #include <asm/uaccess.h>
 
+/*
+ * These routines enable/disable the pagefault handler in that
+ * it will not take any locks and go straight to the fixup table.
+ *
+ * They have great resemblance to the preempt_disable/enable calls
+ * and in fact they are identical; this is because currently there is
+ * no other way to make the pagefault handlers do this. So we do
+ * disable preemption but we don't necessarily care about that.
+ */
+static inline void pagefault_disable(void)
+{
+        inc_preempt_count();
+        /*
+         * make sure to have issued the store before a pagefault
+         * can hit.
+         */
+        barrier();
+}
+
+static inline void pagefault_enable(void)
+{
+        /*
+         * make sure to issue those last loads/stores before enabling
+         * the pagefault handler again.
+         */
+        barrier();
+        dec_preempt_count();
+        /*
+         * make sure we do..
+         */
+        barrier();
+        preempt_check_resched();
+}
+
 #ifndef ARCH_HAS_NOCACHE_UACCESS
 
 static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
@@ -35,9 +70,9 @@ static inline unsigned long __copy_from_user_nocache(void *to,
         ({                                              \
                 long ret;                               \
                                                         \
-                inc_preempt_count();                    \
+                pagefault_disable();                    \
                 ret = __get_user(retval, addr);         \
-                dec_preempt_count();                    \
+                pagefault_enable();                     \
                 ret;                                    \
         })