First attempt at making module robust agains unloading when in use.

Sun May 15 11:56:30 2005  Søren Sandmann  <sandmann@redhat.com>

	* module/sysprof-module.c: First attempt at making module robust
	agains unloading when in use.

ChangeLog

@@ -1,3 +1,8 @@
+Sun May 15 11:56:30 2005  Søren Sandmann  <sandmann@redhat.com>
+
+	* module/sysprof-module.c: First attempt at making module robust
+	agains unloading when in use.
+
 Sun May 15 10:24:09 2005  Soeren Sandmann  <sandmann@redhat.com>
 
 	* Makefile.am, module/Makefile: Do more-or-less what the automake

TODO

@@ -1,4 +1,4 @@
-Before 1.0:
+Before 0.9
 
 * Correctness
 	- When the module is unloaded, kill all processes blocking in read
@@ -9,6 +9,8 @@ Before 1.0:
 	  move them)
 	- Consider expanding a few more levels of a new descendants tree 
 
+Before 1.0:
+
 * Build system
 	- Find out what distributions it actually works on
 	    (ask for sucess/failure-stories in 0.9.x releases)

module/sysprof-module.c

@@ -71,7 +71,22 @@ struct userspace_reader
 /* Access another process' address space.
  * Source/target buffer must be kernel space, 
  * Do not walk the page table directly, use get_user_pages
- */
+*/
+
+static atomic_t ref_count;
+static void ref(void)
+{
+	atomic_inc (&ref_count);
+}
+static void unref(void)
+{
+	atomic_dec (&ref_count);
+	wake_up_interruptible (&wait_for_exit);
+}
+static int refcount(void)
+{
+	return atomic_read (&ref_count);
+}
 
 static struct mm_struct *
 get_mm (struct task_struct *tsk)
@@ -323,8 +338,6 @@ generate_stack_trace(struct task_struct *task,
 		trace->truncated = 0;
 }
 
-DECLARE_WAIT_QUEUE_HEAD (wait_to_be_scanned);
-
 static void
 do_generate (void *data)
 {
@@ -344,6 +357,8 @@ do_generate (void *data)
 	atomic_dec (&(task)->usage);
 	
 	mod_timer(&timer, jiffies + INTERVAL);
+
+	unref();
 }
 
 struct work_struct work;
@@ -351,12 +366,16 @@ struct work_struct work;
 static void
 on_timer(unsigned long dong)
 {
+	if (exiting)
+		return;
+	
 	if (current && current->state == TASK_RUNNING && current->pid != 0)
 	{
 		get_task_struct (current);
 
 		INIT_WORK (&work, do_generate, current);
-		
+
+		ref();
 		schedule_work (&work);
 	}
 	else
@@ -373,12 +392,19 @@ procfile_read(char *buffer,
 	      int *eof,
 	      void *data)
 {
-	if (head == tail)
+	if (exiting)
+		return -EBUSY;
+	
+	ref();
+	if (head == tail) {
+		unref();
 		return -EWOULDBLOCK;
+	}
 	wait_event_interruptible (wait_for_trace, head != tail);
 	*buffer_location = (char *)tail;
 	if (tail++ == &stack_traces[N_TRACES - 1])
 		tail = &stack_traces[0];
+	unref();
 	return sizeof (SysprofStackTrace);
 }
 
@@ -386,19 +412,28 @@ struct proc_dir_entry *trace_proc_file;
 static unsigned int
 procfile_poll(struct file *filp, poll_table *poll_table)
 {
+	if (exiting)
+		return -EBUSY;
+
+	ref();
 	if (head != tail) {
+		unref();
 		return POLLIN | POLLRDNORM;
 	}
 	poll_wait(filp, &wait_for_trace, poll_table);
 	if (head != tail) {
+		unref();
 		return POLLIN | POLLRDNORM;
 	}
+	unref();
 	return 0;
 }
 
 int
 init_module(void)
 {
+	ref();
+	
 	trace_proc_file =
 		create_proc_entry ("sysprof-trace", S_IFREG | S_IRUGO, &proc_root);
 	
@@ -422,10 +457,18 @@ void
 cleanup_module(void)
 {
 	exiting = 1;
+	
+	unref();
+
+	wait_event_interruptible (wait_for_exit, (refcount() == 0));
 
 	del_timer (&timer);
 
 	remove_proc_entry("sysprof-trace", &proc_root);
-	
-	printk(KERN_ALERT "stopping sysprof module\n");
+
+	printk(KERN_ALERT "stopping sysprof module (refcount: %d)\n",
+	       refcount());
 }
+
+module_init (init_module);
+module_exit (cleanup_module);