Changeset b23c88e in mainline for kernel/generic/src/preempt/preemption.c

Timestamp:

2012-07-11T05:45:48Z (12 years ago)

Author:

Adam Hraska <adam.hraska+hos@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

b68ae24

Parents:

9f8745c5

Message:

preemption_disable: Replaced memory barriers with compiler barriers. Added checks if reschedule is needed once preemption is enabled.

File:

• kernel/generic/src/preempt/preemption.c (modified) (3 diffs)

kernel/generic/src/preempt/preemption.c

@@ -38 +38 @@
 #include <preemption.h>
 #include <arch.h>
-#include <arch/asm.h>
-#include <arch/barrier.h>
+#include <compiler/barrier.h>
 #include <debug.h>
+#include <proc/scheduler.h>
 
 /** Increment preemption disabled counter. */
@@ -46 +46 @@
 {
         THE->preemption_disabled++;
-        memory_barrier();
+        compiler_barrier();
 }
 
@@ -52 +52 @@
 void preemption_enable(void)
 {
+        preemption_enable_noresched();
+        
+        if (PREEMPTION_ENABLED && THREAD && THREAD->need_resched) {
+                preemption_enabled_scheduler();
+        }
+}
+
+/** Decrement preemption disabled counter. */
+void preemption_enable_noresched(void)
+{
         ASSERT(PREEMPTION_DISABLED);
-        memory_barrier();
+        compiler_barrier();
         THE->preemption_disabled--;
+}
+
+/** Preemption was enabled. Calls scheduler(). */
+void preemption_enabled_scheduler(void)
+{
+        ASSERT(PREEMPTION_ENABLED);
+        
+        /* 
+         * Avoid a race between a thread about to invoke the scheduler() 
+         * after checking THREAD->need_resched and an interrupt that
+         * occurs right after the check.
+         * 
+         * Also ensures that code that relies on disabled interrupts
+         * to suppress preemption continues to work.
+         */
+        if (!interrupts_disabled()) {
+                scheduler();
+        }
 }