linux-kernel - [PATCH v2 1/2] locking/lockdep: Don't warn class/lock name mismatch for novalidate class

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Date:   Tue, 25 Sep 2018 10:41:08 -0400
From:   Waiman Long <longman@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Arnd Bergmann <arnd@...db.de>, chuhu@...hat.com,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v2 1/2] locking/lockdep: Don't warn class/lock name mismatch for novalidate class

For the special novalidate class (lockdep_set_novalidate_class), multiple
locks with different names may use the same class. The WARN_ON_ONCE()
check in look_up_lock_class() will then report an unnecessary warning.

The current users of lockdep_set_novalidate_class() includes the
device mutex, one mutex and one rwsem in drivers/md/bcache/btree.c.
So the novalidate class is now excluded from the check.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/locking/lockdep.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index dd13f865ad40..10babc35953b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -693,9 +693,12 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
 		if (class->key == key) {
 			/*
 			 * Huh! same key, different name? Did someone trample
-			 * on some memory? We're most confused.
+			 * on some memory? We're most confused unless it is
+			 * __lockdep_no_validate__ where different locks can
+			 * use the same class.
 			 */
-			WARN_ON_ONCE(class->name != lock->name);
+			WARN_ON_ONCE((key != __lockdep_no_validate__.subkeys) &&
+				     (class->name != lock->name));
 			return class;
 		}
 	}
-- 
2.18.0