kmemleak: Protect the seq start/next/stop sequence by rcu_read_lock()

Objects passed to kmemleak_seq_next() have an incremented reference
count (hence not freed) but they may point via object_list.next to
other freed objects. To avoid this, the whole start/next/stop sequence
must be protected by rcu_read_lock().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 5aabd41..4872673 100644 (file)
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1217,7 +1217,6 @@ static void *kmemleak_seq_start(struct seq_file *seq, loff_t *pos)
        }
        object = NULL;
 out:
-       rcu_read_unlock();
        return object;
 }
 
@@ -1233,13 +1232,11 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
        ++(*pos);
 
-       rcu_read_lock();
        list_for_each_continue_rcu(n, &object_list) {
                next_obj = list_entry(n, struct kmemleak_object, object_list);
                if (get_object(next_obj))
                        break;
        }
-       rcu_read_unlock();
 
        put_object(prev_obj);
        return next_obj;
@@ -1255,6 +1252,7 @@ static void kmemleak_seq_stop(struct seq_file *seq, void *v)
                 * kmemleak_seq_start may return ERR_PTR if the scan_mutex
                 * waiting was interrupted, so only release it if !IS_ERR.
                 */
+               rcu_read_unlock();
                mutex_unlock(&scan_mutex);
                if (v)
                        put_object(v);