1 files changed, 53 insertions, 4 deletions

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f2ae8a65f667..ad9afd8c7eb9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2200,6 +2200,44 @@ static inline bool usage_match(struct lock_list *entry, void *mask)
 		return !!((entry->class->usage_mask & LOCKF_IRQ) & *(unsigned long *)mask);
 }
 
+static inline bool usage_skip(struct lock_list *entry, void *mask)
+{
+	/*
+	 * Skip local_lock() for irq inversion detection.
+	 *
+	 * For !RT, local_lock() is not a real lock, so it won't carry any
+	 * dependency.
+	 *
+	 * For RT, an irq inversion happens when we have lock A and B, and on
+	 * some CPU we can have:
+	 *
+	 *	lock(A);
+	 *	<interrupted>
+	 *	  lock(B);
+	 *
+	 * where lock(B) cannot sleep, and we have a dependency B -> ... -> A.
+	 *
+	 * Now we prove local_lock() cannot exist in that dependency. First we
+	 * have the observation for any lock chain L1 -> ... -> Ln, for any
+	 * 1 <= i <= n, Li.inner_wait_type <= L1.inner_wait_type, otherwise
+	 * wait context check will complain. And since B is not a sleep lock,
+	 * therefore B.inner_wait_type >= 2, and since the inner_wait_type of
+	 * local_lock() is 3, which is greater than 2, therefore there is no
+	 * way the local_lock() exists in the dependency B -> ... -> A.
+	 *
+	 * As a result, we will skip local_lock(), when we search for irq
+	 * inversion bugs.
+	 */
+	if (entry->class->lock_type == LD_LOCK_PERCPU) {
+		if (DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
+			return false;
+
+		return true;
+	}
+
+	return false;
+}
+
 /*
  * Find a node in the forwards-direction dependency sub-graph starting
  * at @root->class that matches @bit.
@@ -2215,7 +2253,7 @@ find_usage_forwards(struct lock_list *root, unsigned long usage_mask,
 
 	debug_atomic_inc(nr_find_usage_forwards_checks);
 
-	result = __bfs_forwards(root, &usage_mask, usage_match, NULL, target_entry);
+	result = __bfs_forwards(root, &usage_mask, usage_match, usage_skip, target_entry);
 
 	return result;
 }
@@ -2232,7 +2270,7 @@ find_usage_backwards(struct lock_list *root, unsigned long usage_mask,
 
 	debug_atomic_inc(nr_find_usage_backwards_checks);
 
-	result = __bfs_backwards(root, &usage_mask, usage_match, NULL, target_entry);
+	result = __bfs_backwards(root, &usage_mask, usage_match, usage_skip, target_entry);
 
 	return result;
 }
@@ -2597,7 +2635,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
 	 */
 	bfs_init_rootb(&this, prev);
 
-	ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, NULL, NULL);
+	ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
 	if (bfs_error(ret)) {
 		print_bfs_bug(ret);
 		return 0;
@@ -2664,6 +2702,12 @@ static inline int check_irq_usage(struct task_struct *curr,
 {
 	return 1;
 }
+
+static inline bool usage_skip(struct lock_list *entry, void *mask)
+{
+	return false;
+}
+
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 #ifdef CONFIG_LOCKDEP_SMALL
@@ -2697,7 +2741,12 @@ check_redundant(struct held_lock *src, struct held_lock *target)
 
 	debug_atomic_inc(nr_redundant_checks);
 
-	ret = check_path(target, &src_entry, hlock_equal, NULL, &target_entry);
+	/*
+	 * Note: we skip local_lock() for redundant check, because as the
+	 * comment in usage_skip(), A -> local_lock() -> B and A -> B are not
+	 * the same.
+	 */
+	ret = check_path(target, &src_entry, hlock_equal, usage_skip, &target_entry);
 
 	if (ret == BFS_RMATCH)
 		debug_atomic_inc(nr_redundant);