linux-kernel - [RFC v7 12/19] lockdep: Add recursive read locks into dependency graph

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Date:   Fri,  7 Aug 2020 15:42:31 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC v7 12/19] 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@...il.com>
---
 kernel/locking/lockdep.c | 19 ++-----------------
 1 file changed, 2 insertions(+), 17 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 040509667798..867199c4b85d 100644
--- a/kernel/locking/lockdep.c
+++ b/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;
 
-- 
2.28.0