[PATCH] fix OProfile locking

This makes OProgile use get_task_mm() as discussed.  It also fixes up
Anton's previous patch.  Zwane's soaked this patch all night w/o
problems.

drivers/oprofile/buffer_sync.c

@@ -133,7 +133,7 @@ static struct notifier_block module_load_nb = {
  
 static void end_sync(void)
 {
-	end_cpu_timers();
+	end_cpu_work();
 	/* make sure we don't leak task structs */
 	process_task_mortuary();
 	process_task_mortuary();
@@ -144,7 +144,7 @@ int sync_start(void)
 {
 	int err;
 
-	start_cpu_timers();
+	start_cpu_work();
 
 	err = task_handoff_register(&task_free_nb);
 	if (err)
@@ -342,33 +342,18 @@ static void add_sample(struct mm_struct * mm, struct op_sample * s, int in_kerne
 
 static void release_mm(struct mm_struct * mm)
 {
-	if (mm)
+	if (!mm)
+		return;
 	up_read(&mm->mmap_sem);
+	mmput(mm);
 }
 
 
-/* Take the task's mmap_sem to protect ourselves from
- * races when we do lookup_dcookie().
- */
 static struct mm_struct * take_tasks_mm(struct task_struct * task)
 {
-	struct mm_struct * mm;
-       
-	/* Subtle. We don't need to keep a reference to this task's mm,
-	 * because, for the mm to be freed on another CPU, that would have
-	 * to go through the task exit notifier, which ends up sleeping
-	 * on the buffer_sem we hold, so we end up with mutual exclusion
-	 * anyway.
-	 */
-	task_lock(task);
-	mm = task->mm;
-	task_unlock(task);
- 
-	if (mm) {
-		/* needed to walk the task's VMAs */
+	struct mm_struct * mm = get_task_mm(task);
+	if (mm)
 		down_read(&mm->mmap_sem);
-	}
- 
 	return mm;
 }
 

drivers/oprofile/cpu_buffer.c

@@ -30,7 +30,7 @@ struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned;
 static void wq_sync_buffer(void *);
 
 #define DEFAULT_TIMER_EXPIRE (HZ / 10)
-int timers_enabled;
+int work_enabled;
 
 static void __free_cpu_buffers(int num)
 {
@@ -80,11 +80,11 @@ void free_cpu_buffers(void)
 }
 
 
-void start_cpu_timers(void)
+void start_cpu_work(void)
 {
 	int i;
 
-	timers_enabled = 1;
+	work_enabled = 1;
 
 	for_each_online_cpu(i) {
 		struct oprofile_cpu_buffer * b = &cpu_buffer[i];
@@ -98,11 +98,11 @@ void start_cpu_timers(void)
 }
 
 
-void end_cpu_timers(void)
+void end_cpu_work(void)
 {
 	int i;
 
-	timers_enabled = 0;
+	work_enabled = 0;
 
 	for_each_online_cpu(i) {
 		struct oprofile_cpu_buffer * b = &cpu_buffer[i];
@@ -220,6 +220,6 @@ static void wq_sync_buffer(void * data)
 	sync_buffer(b->cpu);
 
 	/* don't re-add the work if we're shutting down */
-	if (timers_enabled)
+	if (work_enabled)
 		schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 }

drivers/oprofile/cpu_buffer.h

@@ -20,8 +20,8 @@ struct task_struct;
 int alloc_cpu_buffers(void);
 void free_cpu_buffers(void);
 
-void start_cpu_timers(void);
-void end_cpu_timers(void);
+void start_cpu_work(void);
+void end_cpu_work(void);
 
 /* CPU buffer is composed of such entries (which are
  * also used for context switch notes)

kernel/fork.c

@@ -483,6 +483,7 @@ void mmput(struct mm_struct *mm)
 		mmdrop(mm);
 	}
 }
+EXPORT_SYMBOL_GPL(mmput);
 
 /**
  * get_task_mm - acquire a reference to the task's mm
@@ -514,6 +515,7 @@ struct mm_struct *get_task_mm(struct task_struct *task)
 	task_unlock(task);
 	return mm;
 }
+EXPORT_SYMBOL_GPL(get_task_mm);
 
 /* Please note the differences between mmput and mm_release.
  * mmput is called whenever we stop holding onto a mm_struct,