[PATCH 08/15] preempt: Take away preempt_enable_no_resched() from modules

[Peter Zijlstra]

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.

Cc: Eliezer Tamir <eliezer.tamir@xxxxxxxxxxxxxxx>
Cc: rui.zhang@xxxxxxxxx
Cc: jacob.jun.pan@xxxxxxxxxxxxxxx
Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: hpa@xxxxxxxxx
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: lenb@xxxxxxxxxx
Cc: rjw@xxxxxxxxxxxxx
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 include/linux/preempt.h |   22 ++++++++++++++++++++--
 include/linux/uaccess.h |    5 ++++-
 2 files changed, 24 insertions(+), 3 deletions(-)

--- 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 */
@@ -126,6 +134,16 @@ do { \
 #define preempt_fold_need_resched() do { } while (0)
 #endif
 
+#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;
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -25,13 +25,16 @@ static inline void pagefault_disable(voi
 
 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


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