> On 20. 3. 2023, at 19:37, Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> wrote:
>
> On 2023-03-17 17:37, Ondřej Surý via lttng-dev wrote:
>> FIXME: This is experiment that adds explicit memory barrier in the
>> free_completion in the workqueue.c, so ThreadSanitizer knows it's ok to
>> free the resources.
>> Signed-off-by: Ondřej Surý <ond...@sury.org>
>> ---
>> src/workqueue.c | 1 +
>> 1 file changed, 1 insertion(+)
>> diff --git a/src/workqueue.c b/src/workqueue.c
>> index 1039d72..f21907f 100644
>> --- a/src/workqueue.c
>> +++ b/src/workqueue.c
>> @@ -377,6 +377,7 @@ void free_completion(struct urcu_ref *ref)
>> struct urcu_workqueue_completion *completion;
>> completion = caa_container_of(ref, struct urcu_workqueue_completion,
>> ref);
>> + assert(!urcu_ref_get_unless_zero(&completion->ref));
>
> Perhaps what we really want here is an ANNOTATE_UNPUBLISH_MEMORY_RANGE() of
> some sort ?
I guess?
My experience with TSAN tells me, that you need some kind of memory barrier
when using acquire-release
semantics and you do:
if (__atomic_sub_fetch(obj->ref, __ATOMIC_RELEASE) == 0) {
/* __ATOMIC_ACQUIRE needed here */
free(obj);
}
we end up using following code in BIND 9:
if (__atomic_sub_fetch(obj->ref, __ATOMIC_ACQ_REL) == 0) {
free(obj);
}
So, I am guessing after the change of uatomic_sub_return() to __ATOMIC_ACQ_REL,
this patch should no longer be needed.
Ondrej
--
Ondřej Surý (He/Him)
ond...@sury.org
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