kmemleak: Do not trigger a scan when reading the debug/kmemleak file

Since there is a kernel thread for automatically scanning the memory, it
makes sense for the debug/kmemleak file to only show its findings. This
patch also adds support for "echo scan > debug/kmemleak" to trigger an
intermediate memory scan and eliminates the kmemleak_mutex (scan_mutex
covers all the cases now).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 40 insertions, 50 deletions

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 4130a4889fa9..e96e0ec6a56e 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -48,10 +48,10 @@
  *   scanned. This list is only modified during a scanning episode when the
  *   scan_mutex is held. At the end of a scan, the gray_list is always empty.
  *   Note that the kmemleak_object.use_count is incremented when an object is
- *   added to the gray_list and therefore cannot be freed
- * - kmemleak_mutex (mutex): prevents multiple users of the "kmemleak" debugfs
- *   file together with modifications to the memory scanning parameters
- *   including the scan_thread pointer
+ *   added to the gray_list and therefore cannot be freed. This mutex also
+ *   prevents multiple users of the "kmemleak" debugfs file together with
+ *   modifications to the memory scanning parameters including the scan_thread
+ *   pointer
  *
  * The kmemleak_object structures have a use_count incremented or decremented
  * using the get_object()/put_object() functions. When the use_count becomes
@@ -195,10 +195,8 @@ static unsigned long jiffies_min_age;
 static signed long jiffies_scan_wait;
 /* enables or disables the task stacks scanning */
 static int kmemleak_stack_scan = 1;
-/* mutex protecting the memory scanning */
+/* protects the memory scanning, parameters and debug/kmemleak file access */
 static DEFINE_MUTEX(scan_mutex);
-/* mutex protecting the access to the /sys/kernel/debug/kmemleak file */
-static DEFINE_MUTEX(kmemleak_mutex);
 
 /* number of leaks reported (for limitation purposes) */
 static int reported_leaks;
@@ -927,6 +925,7 @@ static void kmemleak_scan(void)
 	struct kmemleak_object *object, *tmp;
 	struct task_struct *task;
 	int i;
+	int new_leaks = 0;
 
 	/* prepare the kmemleak_object's */
 	rcu_read_lock();
@@ -1024,6 +1023,26 @@ static void kmemleak_scan(void)
 		object = tmp;
 	}
 	WARN_ON(!list_empty(&gray_list));
+
+	/*
+	 * Scanning result reporting.
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(object, &object_list, object_list) {
+		spin_lock_irqsave(&object->lock, flags);
+		if (unreferenced_object(object) &&
+		    !(object->flags & OBJECT_REPORTED)) {
+			object->flags |= OBJECT_REPORTED;
+			new_leaks++;
+		}
+		spin_unlock_irqrestore(&object->lock, flags);
+	}
+	rcu_read_unlock();
+
+	if (new_leaks)
+		pr_info("%d new suspected memory leaks (see "
+			"/sys/kernel/debug/kmemleak)\n", new_leaks);
+
 }
 
 /*
@@ -1045,33 +1064,12 @@ static int kmemleak_scan_thread(void *arg)
 	}
 
 	while (!kthread_should_stop()) {
-		struct kmemleak_object *object;
 		signed long timeout = jiffies_scan_wait;
-		int new_leaks = 0;
 
 		mutex_lock(&scan_mutex);
-
 		kmemleak_scan();
-
-		rcu_read_lock();
-		list_for_each_entry_rcu(object, &object_list, object_list) {
-			unsigned long flags;
-
-			spin_lock_irqsave(&object->lock, flags);
-			if (unreferenced_object(object) &&
-			    !(object->flags & OBJECT_REPORTED)) {
-				object->flags |= OBJECT_REPORTED;
-				new_leaks++;
-			}
-			spin_unlock_irqrestore(&object->lock, flags);
-		}
-		rcu_read_unlock();
-
-		if (new_leaks)
-			pr_info("%d new suspected memory leaks (see "
-				"/sys/kernel/debug/kmemleak)\n", new_leaks);
-
 		mutex_unlock(&scan_mutex);
+
 		/* wait before the next scan */
 		while (timeout && !kthread_should_stop())
 			timeout = schedule_timeout_interruptible(timeout);
@@ -1084,7 +1082,7 @@ static int kmemleak_scan_thread(void *arg)
 
 /*
  * Start the automatic memory scanning thread. This function must be called
- * with the kmemleak_mutex held.
+ * with the scan_mutex held.
  */
 void start_scan_thread(void)
 {
@@ -1099,7 +1097,7 @@ void start_scan_thread(void)
 
 /*
  * Stop the automatic memory scanning thread. This function must be called
- * with the kmemleak_mutex held.
+ * with the scan_mutex held.
  */
 void stop_scan_thread(void)
 {
@@ -1119,10 +1117,8 @@ static void *kmemleak_seq_start(struct seq_file *seq, loff_t *pos)
 	struct kmemleak_object *object;
 	loff_t n = *pos;
 
-	if (!n) {
-		kmemleak_scan();
+	if (!n)
 		reported_leaks = 0;
-	}
 	if (reported_leaks >= REPORTS_NR)
 		return NULL;
 
@@ -1206,13 +1202,10 @@ static int kmemleak_open(struct inode *inode, struct file *file)
 	if (!atomic_read(&kmemleak_enabled))
 		return -EBUSY;
 
-	ret = mutex_lock_interruptible(&kmemleak_mutex);
+	ret = mutex_lock_interruptible(&scan_mutex);
 	if (ret < 0)
 		goto out;
 	if (file->f_mode & FMODE_READ) {
-		ret = mutex_lock_interruptible(&scan_mutex);
-		if (ret < 0)
-			goto kmemleak_unlock;
 		ret = seq_open(file, &kmemleak_seq_ops);
 		if (ret < 0)
 			goto scan_unlock;
@@ -1221,8 +1214,6 @@ static int kmemleak_open(struct inode *inode, struct file *file)
 
 scan_unlock:
 	mutex_unlock(&scan_mutex);
-kmemleak_unlock:
-	mutex_unlock(&kmemleak_mutex);
 out:
 	return ret;
 }
@@ -1231,11 +1222,9 @@ static int kmemleak_release(struct inode *inode, struct file *file)
 {
 	int ret = 0;
 
-	if (file->f_mode & FMODE_READ) {
+	if (file->f_mode & FMODE_READ)
 		seq_release(inode, file);
-		mutex_unlock(&scan_mutex);
-	}
-	mutex_unlock(&kmemleak_mutex);
+	mutex_unlock(&scan_mutex);
 
 	return ret;
 }
@@ -1250,6 +1239,7 @@ static int kmemleak_release(struct inode *inode, struct file *file)
  *   scan=off	- stop the automatic memory scanning thread
  *   scan=...	- set the automatic memory scanning period in seconds (0 to
  *		  disable it)
+ *   scan	- trigger a memory scan
  */
 static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 			      size_t size, loff_t *ppos)
@@ -1287,7 +1277,9 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 			jiffies_scan_wait = msecs_to_jiffies(secs * 1000);
 			start_scan_thread();
 		}
-	} else
+	} else if (strncmp(buf, "scan", 4) == 0)
+		kmemleak_scan();
+	else
 		return -EINVAL;
 
 	/* ignore the rest of the buffer, only one command at a time */
@@ -1312,11 +1304,9 @@ static int kmemleak_cleanup_thread(void *arg)
 {
 	struct kmemleak_object *object;
 
-	mutex_lock(&kmemleak_mutex);
+	mutex_lock(&scan_mutex);
 	stop_scan_thread();
-	mutex_unlock(&kmemleak_mutex);
 
-	mutex_lock(&scan_mutex);
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list)
 		delete_object(object->pointer);
@@ -1458,9 +1448,9 @@ static int __init kmemleak_late_init(void)
 				     &kmemleak_fops);
 	if (!dentry)
 		pr_warning("Failed to create the debugfs kmemleak file\n");
-	mutex_lock(&kmemleak_mutex);
+	mutex_lock(&scan_mutex);
 	start_scan_thread();
-	mutex_unlock(&kmemleak_mutex);
+	mutex_unlock(&scan_mutex);
 
 	pr_info("Kernel memory leak detector initialized\n");