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 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. 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/>. -- Olivier Dion EfficiOS Inc. https://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
