Hi Ahmed,
Sorry I was missing some points on title and changelog, please see below and refer to Documentation/process/maintainer-tip.rst:
The title needs to be something like:
locking/lockdep: Avoid creating new name string literals in lockdep_set_subclass()
the title and the changlog needs to be in imperative mode.
On Mon, Jul 15, 2024 at 04:26:37PM +0300, botta633 wrote:
From: Ahmed Ehab bottaawesome633@gmail.com
Preventing lockdep_set_subclass from creating a new instance of the
Same here, s/Preventing/Prevent, and when you reference a function, you want to do "lockdep_set_subclass()" instead of "lockdep_set_subclass".
Besides, overall, you want to structure your changelog as follow:
Syzbot reports a problem that a warning will be triggered while searching a lock class in look_up_lock_class().
// ^ the problem statement
The cause of the issue is that instead of the existing name of a lock class, a new name (a string literal) is created and used by lockdep_set_subclass(), and this results in two lock classes with the same key but different address of the names, and a WARN_ONCE() is triggered because of that in look_up_lock_class().
// ^ the analysis of the problem, you can merge the above two into one // paragraph if that works for you.
To fix this, change lockdep_set_subclass() to use the existing name instead of a new one. As a result no new name will be created by lockdep_set_subclass(), hence the warning is avoided.
// ^ the fix.
Please send a new version if these make sense to you. The patch #2 also needs some changes in the title and changelog, but since that's adding a new test instead of fixing an issue, you could just write something like:
Add a test case to ensure that no new name string literal will be created in lockdep_set_subclass(), otherwise a warning will be triggered in look_up_lock_class(). Add this to catch the problem in the future.
Thanks!
Regards, Boqun
string literal. Hence, we will always have the same class->name among parent and subclasses. This prevents kernel panics when looking up a lock class while comparing class locks and class names.
Reported-by: syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks") Cc: stable@vger.kernel.org Signed-off-by: Ahmed Ehab bottaawesome633@gmail.com
v3->v4: - Fixed subject line truncation.
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