lockdep: Add recursive read locks into dependency graph

Since we have all the fundamental to handle recursive read locks, we now
add them into the dependency graph.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-13-boqun.feng@gmail.com

kernel/locking/lockdep.c

@@ -2808,16 +2808,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	if (!check_irq_usage(curr, prev, next))
 		return 0;
 
-	/*
-	 * For recursive read-locks we do all the dependency checks,
-	 * but we dont store read-triggered dependencies (only
-	 * write-triggered dependencies). This ensures that only the
-	 * write-side dependencies matter, and that if for example a
-	 * write-lock never takes any other locks, then the reads are
-	 * equivalent to a NOP.
-	 */
-	if (next->read == 2 || prev->read == 2)
-		return 1;
 	/*
 	 * Is the <prev> -> <next> dependency already present?
 	 *
@@ -2935,13 +2925,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 		u16 distance = curr->lockdep_depth - depth + 1;
 		hlock = curr->held_locks + depth - 1;
 
-		/*
-		 * Only non-recursive-read entries get new dependencies
-		 * added:
-		 */
-		if (hlock->read != 2 && hlock->check) {
-			int ret = check_prev_add(curr, hlock, next, distance,
-						 &trace);
+		if (hlock->check) {
+			int ret = check_prev_add(curr, hlock, next, distance, &trace);
 			if (!ret)
 				return 0;