Re: [PATCH] locking/mutex: add MUTEX_WARN_ON() into fast path

[Waiman Long <llong@redhat.com>]

On 2/20/25 7:49 AM, yunhui cui wrote:
> Hi All,
>
> Gentle ping. Any comments on this patch?
>
> On Sun, Jan 26, 2025 at 11:32 AM Yunhui Cui <cuiyunhui@bytedance.com> wrote:
>> Scenario: In platform_device_register, the driver misuses struct
>> device as platform_data, making kmemdup duplicate a device. Accessing
>> the duplicate may cause list corruption due to its mutex magic or list
>> holding old content.
>> It recurs randomly as the first mutex - getting process skips the slow
>> path and mutex check. Adding MUTEX_WARN_ON(lock->magic!= lock) in
>> __mutex_trylock_fast() makes it always happen.
>>
>> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
>> ---
>>   kernel/locking/mutex.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
>> index b36f23de48f1..19b636f60a24 100644
>> --- a/kernel/locking/mutex.c
>> +++ b/kernel/locking/mutex.c
>> @@ -143,6 +143,8 @@ static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
>>          unsigned long curr = (unsigned long)current;
>>          unsigned long zero = 0UL;
>>
>> +       MUTEX_WARN_ON(lock->magic != lock);
>> +
>>          if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
>>                  return true;
>>
>> --
>> 2.39.2
>>
LGTM

Acked-by: Waiman Long <longman@redhat.com>