On 1/20/2023 4:54 PM, Paul E. McKenney wrote:
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);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.
I think the import question is "is this a harmful data race (and needs to be fixed as proposed by the patch) or a harmless one (and we should use data_race() to silence tools)?".
In https://lkml.org/lkml/2023/1/22/160 I describe how this data race can affect important ordering guarantees for the rest of the code. For this reason I consider it a harmful one. If this is not the case, I would appreciate some feedback or pointer to resources about what races care to avoid spamming the mailing list in the future.
Hernan