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");