From 62b94a08da1bae9d187d49dfcd6665af393750f8 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 20 Nov 2013 16:52:19 +0100
Subject: [PATCH] sched/preempt: Take away preempt_enable_no_resched() from
 modules

Discourage drivers/modules to be creative with preemption.

Sadly all is implemented in macros and inline so if they want to do
evil they still can, but at least try and discourage some.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: rui.zhang@intel.com
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-fn7h6vu8wtgxk0ih402qcijx@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/preempt.h | 22 ++++++++++++++++++++--
 include/linux/uaccess.h |  5 ++++-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index a3d9dc8c2c00..dd9ddf8af205 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -64,7 +64,11 @@ do { \
 } while (0)
 
 #else
-#define preempt_enable() preempt_enable_no_resched()
+#define preempt_enable() \
+do { \
+	barrier(); \
+	preempt_count_dec(); \
+} while (0)
 #define preempt_check_resched() do { } while (0)
 #endif
 
@@ -93,7 +97,11 @@ do { \
 		__preempt_schedule_context(); \
 } while (0)
 #else
-#define preempt_enable_notrace() preempt_enable_no_resched_notrace()
+#define preempt_enable_notrace() \
+do { \
+	barrier(); \
+	__preempt_count_dec(); \
+} while (0)
 #endif
 
 #else /* !CONFIG_PREEMPT_COUNT */
@@ -116,6 +124,16 @@ do { \
 
 #endif /* CONFIG_PREEMPT_COUNT */
 
+#ifdef MODULE
+/*
+ * Modules have no business playing preemption tricks.
+ */
+#undef sched_preempt_enable_no_resched
+#undef preempt_enable_no_resched
+#undef preempt_enable_no_resched_notrace
+#undef preempt_check_resched
+#endif
+
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 
 struct preempt_notifier;
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 9d8cf056e661..ecd3319dac33 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -25,13 +25,16 @@ static inline void pagefault_disable(void)
 
 static inline void pagefault_enable(void)
 {
+#ifndef CONFIG_PREEMPT
 	/*
 	 * make sure to issue those last loads/stores before enabling
 	 * the pagefault handler again.
 	 */
 	barrier();
 	preempt_count_dec();
-	preempt_check_resched();
+#else
+	preempt_enable();
+#endif
 }
 
 #ifndef ARCH_HAS_NOCACHE_UACCESS
-- 
2.20.1