linux-kernel - [PATCH v2] lockdep: report name and key when look_up_lock

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Date:   Mon, 19 Sep 2022 09:52:13 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Boqun Feng <boqun.feng@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] lockdep: report name and key when look_up_lock_class() got
 confused

Printing this information will be helpful.

  ------------[ cut here ]------------
  Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
  WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
  Modules linked in:
  CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
  Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
  RIP: 0010:look_up_lock_class+0xcc/0x140

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Changes in v2:
  Make message more human readable, suggested by Boqun Feng <boqun.feng@...il.com>.

 kernel/locking/lockdep.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 64a13eb56078..e3375bc40dad 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -934,8 +934,10 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
 			 * Huh! same key, different name? Did someone trample
 			 * on some memory? We're most confused.
 			 */
-			WARN_ON_ONCE(class->name != lock->name &&
-				     lock->key != &__lockdep_no_validate__);
+			WARN_ONCE(class->name != lock->name &&
+				  lock->key != &__lockdep_no_validate__,
+				  "Looking for class \"%s\" with key %ps, but found a different class \"%s\" with the same key\n",
+				  lock->name, lock->key, class->name);
 			return class;
 		}
 	}
-- 
2.34.1