Hey,
we use ThreadSanitizer in BIND 9 CI quite extensively and with userspace-rcu
it's lit like an American house on Saturnalia ;).
I have two questions:
1. I've tried to help TSAN by replacing the custom atomics with __atomic gcc
primitives - that seems to work pretty well. Note that using C11 stdatomics
is frankly not possible here because it would require wrapping everything into
_Atomic().
Do you want me to contribute this back? And how should I plug this into the
existing structure? This touches:
include/urcu/static/pointer.h
include/urcu/system.h
include/urcu/uatomic.h
2. I know there's KTSAN, so it must work somehow, but was there any success
on using ThreadSanitizer on projects using Userspace-RCU? It mostly seems
to highlight the CDS parts of the code.
I can help TSAN to understand some of the code or suppress some of the warnings,
but I do want to prevent the code to be full of stuff like this:
static void
destroy_adbname_rcu_head(struct rcu_head *rcu_head) {
dns_adbname_t *adbname = caa_container_of(rcu_head, dns_adbname_t,
rcu_head);
#ifdef __SANITIZE_THREAD__
SPINLOCK(&adbname->lock);
SPINUNLOCK(&adbname->lock);
#endif
destroy_adbname(adbname);
}
I am absolutely sure that the adbname can be destroyed here (because of the
reference counting), but TSAN had a problem with it. Doing the "fake" barrier
with a spinlock here made it stop consider this to be a data race.
I also had to disable the auto_resize of cds_lfht when running under TSAN.
I am also worried that by hiding some code from TSAN, we might miss a legitimate
error.
All I found using Google was this notice from 2014:
https://www.mail-archive.com/valgrind-users@lists.sourceforge.net/msg05121.html
and perhaps this:
https://github.com/google/sanitizers/issues/1415
(Perhaps, I should look into annotating urcu code with TSAN annotations?)
~~~~
3. As an extra bonus, this is going to be needed with clang-17 as noreturn is
now
reserved word:
diff --git a/include/urcu/uatomic/generic.h b/include/urcu/uatomic/generic.h
index 89d1cfa..c3762b0 100644
--- a/include/urcu/uatomic/generic.h
+++ b/include/urcu/uatomic/generic.h
@@ -38,7 +38,7 @@ extern "C" {
#endif
#if !defined __OPTIMIZE__ || defined UATOMIC_NO_LINK_ERROR
-static inline __attribute__((always_inline, noreturn))
+static inline __attribute__((always_inline, __noreturn__))
void _uatomic_link_error(void)
{
#ifdef ILLEGAL_INSTR
diff --git a/src/urcu-call-rcu-impl.h b/src/urcu-call-rcu-impl.h
index 187727e..cc76f53 100644
--- a/src/urcu-call-rcu-impl.h
+++ b/src/urcu-call-rcu-impl.h
@@ -1055,7 +1055,7 @@ void urcu_register_rculfhash_atfork(struct urcu_atfork
*atfork)
* This unregistration function is deprecated, meant only for internal
* use by rculfhash.
*/
-__attribute__((noreturn))
+__attribute__((__noreturn__))
void urcu_unregister_rculfhash_atfork(struct urcu_atfork *atfork
__attribute__((unused)))
{
urcu_die(EPERM);
Ondrej
--
Ondřej Surý (He/Him)
ond...@sury.org
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