On Tue, 16 May 2023 at 17:47, Olivier Dion <od...@efficios.com> wrote: > > On Tue, 16 May 2023, Dmitry Vyukov via lttng-dev <lttng-dev@lists.lttng.org> > wrote: > > On Mon, 15 May 2023 at 22:18, Olivier Dion <od...@efficios.com> wrote: > > Hi Dmitry, > > > Where can I see the actual changes? Preferably side-by-side diffs with > > full context. Are they (or can they be) uploaded somewhere on > > github/gerrit? > > Here's the link to the first patch of the set on our Gerrit > <https://review.lttng.org/c/userspace-rcu/+/9737>. > > > Are there any remaining open questions? > > On the Gerrit no. But I would add this for the known issues: > > We have a regression test for forking. We get the following when > running it: > > ==23432==ThreadSanitizer: starting new threads after multi-threaded fork is > not supported. Dying (set die_after_fork=0 to override)
> With TSAN_OPTIONS=die_after_fork=0, here are the results for GCC and > Clang. > > * gcc 11.3.0 > ==25266==ThreadSanitizer: dup thread with used id 0x7fd40dafe600 > > Looks like this was fixed with recent merged of TSAN in gcc 13. > > * clang 14.0.6 Hi Olivier, Forking under tsan is a bit tricky. But I see we now take a number of internal mutexes around fork (but I think still not all of them), so maybe it's not that bad. If TSAN_OPTIONS=die_after_fork=0 works reasonably reliably for you, then export it for testing. Older compilers are missing a number of bug fixes. So if you can restrict testing to newer compilers only, that's the way to go. > Tests pass but are very slow. This seems to be because we're calling > exit(3) in the childs. Changing it to _exit(2) solves the issue. The > only thing I can think of is that exit(3) is not async-signal-safe like > _exit(2), yet we do other none-async safe calls like malloc(3) and > free(3) in the childs. By default tsan sleeps for 1 second at exit, since exit sequence is a common source of races. Perhaps it's just these sleeps. Try TSAN_OPTIONS=atexit_sleep_ms=0 (or maybe =50). > Here are some perf records of that: > > With exit(3) > ``` > 12.35% test_urcu_fork. [unknown] [k] 0xffffffff89ebd22b > 8.69% test_urcu_fork. [unknown] [k] 0xffffffff89ebd8fa > 7.50% test_urcu_fork. [unknown] [k] 0xffffffff8a001360 > 6.11% test_urcu_fork. test_urcu_fork.tap [.] > __sanitizer::internal_memset > 5.85% test_urcu_fork. test_urcu_fork.tap [.] __tsan::ForkChildAfter > 1.96% test_urcu_fork. [unknown] [k] 0xffffffff892f8efd > 1.88% test_urcu_fork. [unknown] [k] 0xffffffff89ec8e2c > 1.29% test_urcu_fork. [unknown] [k] 0xffffffff890a99d1 > 0.79% test_urcu_fork. [unknown] [k] 0xffffffff8918c566 > 0.75% test_urcu_fork. test_urcu_fork.tap [.] > __sanitizer::ThreadRegistry::OnFork > 0.71% test_urcu_fork. [unknown] [k] 0xffffffff89349574 > 0.64% test_urcu_fork. [unknown] [k] 0xffffffff89ee424f > 0.57% test_urcu_fork. test_urcu_fork.tap [.] > __tsan::MetaMap::AllocBlock > 0.55% test_urcu_fork. [unknown] [k] 0xffffffff89367249 > 0.53% test_urcu_fork. test_urcu_fork.tap [.] __tsan_read8 > 0.51% test_urcu_fork. [unknown] [k] 0xffffffff89ec8e05 > ``` > > With _exit(2) > ``` > 12.26% test_urcu_fork. [unknown] [k] 0xffffffff89ebd8fa > 9.51% test_urcu_fork. [unknown] [k] 0xffffffff89ebd22b > 6.78% test_urcu_fork. test_urcu_fork.tap [.] > __sanitizer::internal_memset > 6.49% test_urcu_fork. [unknown] [k] 0xffffffff8a001360 > 4.92% test_urcu_fork. test_urcu_fork.tap [.] __tsan::ForkChildAfter > 2.92% test_urcu_fork. [unknown] [k] 0xffffffff892f8efd > 2.19% test_urcu_fork. [unknown] [k] 0xffffffff89ec8e2c > 1.88% test_urcu_fork. [unknown] [k] 0xffffffff890a99d1 > 0.83% test_urcu_fork. test_urcu_fork.tap [.] > __tsan::MetaMap::AllocBlock > 0.72% test_urcu_fork. [unknown] [k] 0xffffffff892f8f1c > 0.67% test_urcu_fork. [unknown] [k] 0xffffffff8918c566 > 0.65% test_urcu_fork. [unknown] [k] 0xffffffff89ec16dd > 0.62% test_urcu_fork. test_urcu_fork.tap [.] > __sanitizer::CombinedAllocator<__sanitizer::SizeClassAllocator32<__sanitizer::AP32>, > __sanitizer::LargeMmapAllocatorPtrArrayStatic>::Allocate > 0.61% test_urcu_fork. test_urcu_fork.tap [.] __tsan_write4 > 0.60% test_urcu_fork. [unknown] [k] 0xffffffff89367249 > 0.59% test_urcu_fork. [unknown] [k] 0xffffffff89ee424f > 0.50% test_urcu_fork. test_urcu_fork.tap [.] > __sanitizer::ThreadRegistry::OnFork > 0.50% test_urcu_fork. test_urcu_fork.tap [.] __tsan_write8 > 0.47% test_urcu_fork. test_urcu_fork.tap [.] __tsan::ForkBefore > 0.45% test_urcu_fork. test_urcu_fork.tap [.] __tsan_func_entry > ``` > > > Is there CI coverage with -fsanitize=thread? > > Since the urcu-signal flavor deadlocks with TSAN (see reproducer in > commit log), the CI simply timeouts. I do however have a job with TSAN > as an matrix axis here <https://ci.lttng.org/job/dev_odion_liburcu/>. Sounds good. _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
