linux-kernel - [PATCH v5 1/2] locking/lockdep: Avoid creating new name string literals in lockdep_set

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Message-ID: <20240824221031.7751-1-bottaawesome633@gmail.com>
Date: Sun, 25 Aug 2024 01:10:30 +0300
From: Ahmed Ehab <bottaawesome633@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	linux-ext4@...r.kernel.org,
	syzkaller@...glegroups.com,
	syzbot+7f4a6f7f7051474e40ad@...kaller.appspotmail.com,
	stable@...r.kernel.org
Subject: [PATCH v5 1/2] locking/lockdep: Avoid creating new name string literals in lockdep_set_subclass()

Syzbot reports a problem that a warning will be triggered while
searching a lock class in look_up_lock_class().

The cause of the issue is that a new name is created and used by
lockdep_set_subclass() instead of using the existing one. This results
in two lock classes with the same key but different name pointers and a
WARN_ONCE() is triggered because of that in look_up_lock_class().

To fix this, change lockdep_set_subclass() to use the existing name
instead of a new one. Hence, no new name will be created by
lockdep_set_subclass(). Hence, the warning is avoided.

Reported-by: <syzbot+7f4a6f7f7051474e40ad@...kaller.appspotmail.com>
Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
Cc: <stable@...r.kernel.org>
Signed-off-by: Ahmed Ehab <bottaawesome633@...il.com>
---
v4->v5:
    - Changed the subject
    - Changed the changelog to be more detailed

 include/linux/lockdep.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 08b0d1d9d78b..df8fa5929de7 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -173,7 +173,7 @@ static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
 			      (lock)->dep_map.lock_type)
 
 #define lockdep_set_subclass(lock, sub)					\
-	lockdep_init_map_type(&(lock)->dep_map, #lock, (lock)->dep_map.key, sub,\
+	lockdep_init_map_type(&(lock)->dep_map, (lock)->dep_map.name, (lock)->dep_map.key, sub,\
 			      (lock)->dep_map.wait_type_inner,		\
 			      (lock)->dep_map.wait_type_outer,		\
 			      (lock)->dep_map.lock_type)
-- 
2.45.2