Annotate LOG_EVERY_N macros as a benign race for TSAN #263
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Summary: Issue google#80 points out several places in glog where TSAN discovers false positives. One of these places is in the `LOG_EVERY_N` macros. These macros are implemented by maintaining a static unprotected integer counter, and TSAN will report data races on these counters. Here is a minimum example to reproduce the data race: ``` void logging() { for (int i = 0; i < 300; ++i) { LOG_EVERY_N(INFO, 2) << "foo"; } } int main() { auto t1 = std::thread(logging); auto t2 = std::thread(logging); t1.join(); t2.join(); return 0; } ``` And here is the TSAN report: ``` WARNING: ThreadSanitizer: data race (pid=776850) Write of size 4 at 0x558de483f684 by thread T2: #0 logging() google#1 void std::_Bind_simple<void (*())()>::_M_invoke<>(std::_Index_tuple<>) google#2 std::_Bind_simple<void (*())()>::operator()() google#3 std::thread::_Impl<std::_Bind_simple<void (*())()> >::_M_run() google#4 execute_native_thread_routine Previous write of size 4 at 0x558de483f684 by thread T1: #0 logging() google#1 void std::_Bind_simple<void (*())()>::_M_invoke<>(std::_Index_tuple<>) google#2 std::_Bind_simple<void (*())()>::operator()() google#3 std::thread::_Impl<std::_Bind_simple<void (*())()> >::_M_run() google#4 execute_native_thread_routine Location is global '<null>' at 0x000000000000 (main+0x00000011c684) Thread T2 (tid=776857, running) created by main thread at: #0 pthread_create google#1 __gthread_create google#2 std::thread::_M_start_thread(std::shared_ptr<std::thread::_Impl_base>, void (*)()) google#3 main Thread T1 (tid=776856, running) created by main thread at: #0 pthread_create google#1 __gthread_create google#2 std::thread::_M_start_thread(std::shared_ptr<std::thread::_Impl_base>, void (*)()) google#3 main SUMMARY: ThreadSanitizer: data race in logging() ``` To avoid noisy TSAN reports and also avoid adding a performance hit, this change will mark these counters as benign races so that TSAN will not report them. This change will only have an effect if we are compiling with TSAN; there are no changes if we are not building with TSAN. With this change, the above example no longer reports a data race when built and run with TSAN.
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I'm seeing error when using this in combination with Abseil, which also defines these: I haven't had a chance to look into what exactly is the appropriate way to not have them conflict, but the error I'm seeing results from the same file using LOG and absl::Status in the same file under tsan.
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It looks like |
Looks like Abseil also has that, just hidden in a preprocessor define. I'm used to seeing the abseil version. I didn't realize it could be applied to a specific function. |
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I see. The other difference that stands out is the type of the size parameter. Glog uses void AnnotateBenignRaceSized(const char *file, int line, const volatile void *mem, long size, const char *description);whereas absl void AnnotateBenignRaceSized(const char* file, int line, const volatile void* address, size_t size, const char* description); |
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Ahh, thanks for point that out. Changing it to size_t fixed things for me. I opened #706. |
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I'm seeing effectively the same issue with |
Before or after #706? |
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In 0.5, so before. Good to see someone's addressed it already. |
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Seems like it. Once 0.6 is released this will be resolved. For now I just implemented an exclusion in my tests. |
Summary:
Issue #80 points out several places in glog where TSAN discovers
false positives. One of these places is in the
LOG_EVERY_Nmacros.These macros are implemented by maintaining a static unprotected
integer counter, and TSAN will report data races on these counters.
Here is a minimum example to reproduce the data race:
And here is the TSAN report:
To avoid noisy TSAN reports and also avoid adding a performance hit, this
change will mark these counters as benign races so that TSAN will not report
them. This change will only have an effect if we are compiling with TSAN;
there are no changes if we are not building with TSAN.
With this change, the above example no longer reports a data race when built
and run with TSAN.