linux-kernel - [PATCH 1/2] locking/lockdep: Cleanup reinit

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Date:   Thu, 10 Feb 2022 22:55:25 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] locking/lockdep: Cleanup reinit_class()

Replace the duplicated WARN_ON_ONCE() tests in reinit_class() with
BUILD_BUG_ON().

Signed-off-by: Waiman Long <longman@...hat.com>
---
 include/linux/lockdep_types.h | 4 ++++
 kernel/locking/lockdep.c      | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index d22430840b53..446d981ae3a2 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -108,6 +108,10 @@ struct lock_class {
 	 */
 	struct list_head		locks_after, locks_before;
 
+	/*
+	 * All the fields that require re-initialization after being zapped
+	 * must be put after "key".
+	 */
 	const struct lockdep_subclass_key *key;
 	unsigned int			subclass;
 	unsigned int			dep_gen_id;
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index d4252b5c9863..77bbe557d48b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6015,10 +6015,10 @@ static void reinit_class(struct lock_class *class)
 	WARN_ON_ONCE(!class->lock_entry.next);
 	WARN_ON_ONCE(!list_empty(&class->locks_after));
 	WARN_ON_ONCE(!list_empty(&class->locks_before));
+	BUILD_BUG_ON(offsetof(struct lock_class, lock_entry) > offset);
+	BUILD_BUG_ON(offsetof(struct lock_class, locks_after) > offset);
+	BUILD_BUG_ON(offsetof(struct lock_class, locks_before) > offset);
 	memset(p + offset, 0, sizeof(*class) - offset);
-	WARN_ON_ONCE(!class->lock_entry.next);
-	WARN_ON_ONCE(!list_empty(&class->locks_after));
-	WARN_ON_ONCE(!list_empty(&class->locks_before));
 }
 
 static inline int within(const void *addr, void *start, unsigned long size)
-- 
2.27.0