Re: [PATCH] Fix data race in mark_rt_mutex_waiters

[Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>]

On 1/20/2023 5:55 AM, Hernan Ponce de Leon wrote:
> From: Hernan Ponce de Leon <hernanl.leon@xxxxxxxxxx>

>   kernel/locking/rtmutex.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 010cf4e6d0b8..7ed9472edd48 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -235,7 +235,7 @@ static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
>   	unsigned long owner, *p = (unsigned long *) &lock->owner;
>   
>   	do {
> -		owner = *p;
> +		owner = READ_ONCE(*p);
>   	} while (cmpxchg_relaxed(p, owner,


I don't see how this makes any difference at all.
*p can be read a dozen times and it's fine; cmpxchg has barrier semantics for compilers afaics