Messages in this thread | | | Date | Fri, 20 Jan 2023 07:54:39 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] Fix data race in mark_rt_mutex_waiters |
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On Fri, Jan 20, 2023 at 06:58:20AM -0800, Arjan van de Ven wrote: > On 1/20/2023 5:55 AM, Hernan Ponce de Leon wrote: > > From: Hernan Ponce de Leon <hernanl.leon@huawei.com> > > > > > 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
Doing so does suppress a KCSAN warning. You could also use data_race() if it turns out that the volatile semantics would prevent a valuable compiler optimization.
Thanx, Paul
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