fix(userspace/falco): fix watchdog race condition on timeout exchange by irozzo-1A · Pull Request #3820 · falcosecurity/falco

irozzo-1A · 2026-03-12T08:52:12Z

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

/kind release

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Uncomment one (or more) /area <> lines:

/area build

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What this PR does / why we need it:

The watchdog thread and stop() consume the timeout pointer with m_timeout.exchange(nullptr, ...). That exchange was using memory_order_release. The load part of the RMW needs acquire semantics so it synchronizes-with the release store in set_timeout()/cancel_timeout(); otherwise the consumer can see the pointer value without seeing the writes that initialized the timeout_data and payload (data race).
Use memory_order_acq_rel on the consumer exchanges so the load synchronizes-with the producer and the pointed-to memory is visible before use.

==================
WARNING: ThreadSanitizer: data race (pid=138643)
  Read of size 8 at 0xff70f48651f0 by thread T11:
    #0 watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::timeout_data::operator=(watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::timeout_data const&) /workspaces/falco/userspace/falco/watchdog.h:75:9 (falco+0x399764) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()::operator()() const /workspaces/falco/userspace/falco/watchdog.h:40:11 (falco+0x399764)
    #2 void std::__invoke_impl<void, watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>(std::__invoke_other, watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:61:14 (falco+0x399614) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #3 std::__invoke_result<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>::type std::__invoke<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>(watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:96:14 (falco+0x399614)
    #4 void std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>::_M_invoke<0ul>(std::_Index_tuple<0ul>) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:292:13 (falco+0x399614)
    #5 std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>::operator()() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:299:11 (falco+0x399614)
    #6 std::thread::_State_impl<std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>>::_M_run() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:244:13 (falco+0x399614)
    #7 <null> <null> (libstdc++.so.6+0xe1adc) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)

  Previous write of size 8 at 0xff70f48651f0 by thread T10:
    #0 operator new(unsigned long) <null> (falco+0x23c3a0) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::cancel_timeout() /workspaces/falco/userspace/falco/watchdog.h:70:29 (falco+0x392518) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #2 falco_outputs::worker() /workspaces/falco/userspace/falco/falco_outputs.cpp:318:6 (falco+0x392518)
    #3 void std::__invoke_impl<void, void (falco_outputs::*)() noexcept, falco_outputs*>(std::__invoke_memfun_deref, void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:74:14 (falco+0x3982ac) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #4 std::__invoke_result<void (falco_outputs::*)() noexcept, falco_outputs*>::type std::__invoke<void (falco_outputs::*)() noexcept, falco_outputs*>(void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:96:14 (falco+0x3982ac)
    #5 void std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:292:13 (falco+0x3982ac)
    #6 std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::operator()() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:299:11 (falco+0x3982ac)
    #7 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>>::_M_run() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:244:13 (falco+0x3982ac)
    #8 <null> <null> (libstdc++.so.6+0xe1adc) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)

  As if synchronized via sleep:
    #0 nanosleep <null> (falco+0x1af658) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 void std::this_thread::sleep_for<long, std::ratio<1l, 1000l>>(std::chrono::duration<long, std::ratio<1l, 1000l>> const&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/this_thread_sleep.h:80:9 (falco+0x399948) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #2 watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()::operator()() const /workspaces/falco/userspace/falco/watchdog.h:48:5 (falco+0x399948)
    #3 void std::__invoke_impl<void, watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>(std::__invoke_other, watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:61:14 (falco+0x399614) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #4 std::__invoke_result<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>::type std::__invoke<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>(watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:96:14 (falco+0x399614)
    #5 void std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>::_M_invoke<0ul>(std::_Index_tuple<0ul>) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:292:13 (falco+0x399614)
    #6 std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>::operator()() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:299:11 (falco+0x399614)
    #7 std::thread::_State_impl<std::thread::_Invoker<std::tuple<watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::start(std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)>, std::chrono::duration<long, std::ratio<1l, 1000l>>)::'lambda'()>>>::_M_run() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:244:13 (falco+0x399614)
    #8 <null> <null> (libstdc++.so.6+0xe1adc) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)

  Location is heap block of size 40 at 0xff70f48651f0 allocated by thread T10:
    #0 operator new(unsigned long) <null> (falco+0x23c3a0) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::cancel_timeout() /workspaces/falco/userspace/falco/watchdog.h:70:29 (falco+0x392518) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #2 falco_outputs::worker() /workspaces/falco/userspace/falco/falco_outputs.cpp:318:6 (falco+0x392518)
    #3 void std::__invoke_impl<void, void (falco_outputs::*)() noexcept, falco_outputs*>(std::__invoke_memfun_deref, void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:74:14 (falco+0x3982ac) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #4 std::__invoke_result<void (falco_outputs::*)() noexcept, falco_outputs*>::type std::__invoke<void (falco_outputs::*)() noexcept, falco_outputs*>(void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:96:14 (falco+0x3982ac)
    #5 void std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:292:13 (falco+0x3982ac)
    #6 std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::operator()() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:299:11 (falco+0x3982ac)
    #7 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>>::_M_run() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:244:13 (falco+0x3982ac)
    #8 <null> <null> (libstdc++.so.6+0xe1adc) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)

  Thread T11 (tid=138656, running) created by thread T10 at:
    #0 pthread_create <null> (falco+0x1b27b8) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State>>, void (*)()) <null> (libstdc++.so.6+0xe1c64) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)
    #2 falco_outputs::worker() /workspaces/falco/userspace/falco/falco_outputs.cpp:295:5 (falco+0x3923ec) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #3 void std::__invoke_impl<void, void (falco_outputs::*)() noexcept, falco_outputs*>(std::__invoke_memfun_deref, void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:74:14 (falco+0x3982ac) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #4 std::__invoke_result<void (falco_outputs::*)() noexcept, falco_outputs*>::type std::__invoke<void (falco_outputs::*)() noexcept, falco_outputs*>(void (falco_outputs::*&&)() noexcept, falco_outputs*&&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:96:14 (falco+0x3982ac)
    #5 void std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:292:13 (falco+0x3982ac)
    #6 std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>::operator()() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:299:11 (falco+0x3982ac)
    #7 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (falco_outputs::*)() noexcept, falco_outputs*>>>::_M_run() /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_thread.h:244:13 (falco+0x3982ac)
    #8 <null> <null> (libstdc++.so.6+0xe1adc) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)

  Thread T10 (tid=138655, running) created by main thread at:
    #0 pthread_create <null> (falco+0x1b27b8) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State>>, void (*)()) <null> (libstdc++.so.6+0xe1c64) (BuildId: 7c239d1743727054caa3df1ab866bfa72cd4dd93)
    #2 void std::_Construct<falco_outputs, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(falco_outputs*, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/stl_construct.h:119:25 (falco+0x2a6258) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #3 void std::allocator_traits<std::allocator<void>>::construct<falco_outputs, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(std::allocator<void>&, falco_outputs*, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/alloc_traits.h:661:4 (falco+0x2a5c18) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #4 std::_Sp_counted_ptr_inplace<falco_outputs, std::allocator<void>, (__gnu_cxx::_Lock_policy)2>::_Sp_counted_ptr_inplace<std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(std::allocator<void>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/shared_ptr_base.h:604:4 (falco+0x2a5c18)
    #5 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count<falco_outputs, std::allocator<void>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(falco_outputs*&, std::_Sp_alloc_shared_tag<std::allocator<void>>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/shared_ptr_base.h:972:6 (falco+0x2a5c18)
    #6 std::__shared_ptr<falco_outputs, (__gnu_cxx::_Lock_policy)2>::__shared_ptr<std::allocator<void>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(std::_Sp_alloc_shared_tag<std::allocator<void>>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/shared_ptr_base.h:1712:14 (falco+0x2a5c18)
    #7 std::shared_ptr<falco_outputs>::shared_ptr<std::allocator<void>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(std::_Sp_alloc_shared_tag<std::allocator<void>>, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/shared_ptr.h:464:4 (falco+0x2a5c18)
    #8 std::shared_ptr<std::enable_if<!is_array<falco_outputs>::value, falco_outputs>::type> std::make_shared<falco_outputs, std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&>(std::shared_ptr<falco_engine>&, std::vector<falco::outputs::config, std::allocator<falco::outputs::config>>&, bool&, bool&, bool&, bool&, bool&, unsigned int&, bool&, unsigned long&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/shared_ptr.h:1009:14 (falco+0x2a5c18)
    #9 falco::app::actions::init_outputs(falco::app::state&) /workspaces/falco/userspace/falco/app/actions/init_outputs.cpp:60:14 (falco+0x2a5c18)
    #10 falco::app::run_result std::__invoke_impl<falco::app::run_result, falco::app::run_result (*&)(falco::app::state&), falco::app::state&>(std::__invoke_other, falco::app::run_result (*&)(falco::app::state&), falco::app::state&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:61:14 (falco+0x24494c) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #11 std::enable_if<is_invocable_r_v<falco::app::run_result, falco::app::run_result (*&)(falco::app::state&), falco::app::state&>, falco::app::run_result>::type std::__invoke_r<falco::app::run_result, falco::app::run_result (*&)(falco::app::state&), falco::app::state&>(falco::app::run_result (*&)(falco::app::state&), falco::app::state&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/invoke.h:114:9 (falco+0x24494c)
    #12 std::_Function_handler<falco::app::run_result (falco::app::state&), falco::app::run_result (*)(falco::app::state&)>::_M_invoke(std::_Any_data const&, falco::app::state&) /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_function.h:290:9 (falco+0x24494c)
    #13 std::function<falco::app::run_result (falco::app::state&)>::operator()(falco::app::state&) const /usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/std_function.h:591:9 (falco+0x23ee18) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #14 falco::app::run(falco::app::state&, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /workspaces/falco/userspace/falco/app/app.cpp:95:44 (falco+0x23ee18)
    #15 falco::app::run(int, char**, bool&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) /workspaces/falco/userspace/falco/app/app.cpp:48:9 (falco+0x23e604) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #16 falco_run(int, char**, bool&) /workspaces/falco/userspace/falco/falco.cpp:44:7 (falco+0x23d520) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)
    #17 main /workspaces/falco/userspace/falco/falco.cpp:67:14 (falco+0x23d810) (BuildId: abf30f4ef9ddb047e7bb5604c3628bf69cfba945)

SUMMARY: ThreadSanitizer: data race /workspaces/falco/userspace/falco/watchdog.h:75:9 in watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::timeout_data::operator=(watchdog<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>>::timeout_data const&)
==================

Which issue(s) this PR fixes:

Fixes #

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Does this PR introduce a user-facing change?:

fix(userspace/falco): fix race condition in watchdog

The watchdog thread and stop() consume the timeout pointer with m_timeout.exchange(nullptr, ...). That exchange was using memory_order_release. The load part of the RMW needs acquire semantics so it synchronizes-with the release store in set_timeout()/cancel_timeout(); otherwise the consumer can see the pointer value without seeing the writes that initialized the timeout_data and payload (data race). Use memory_order_acq_rel on the consumer exchanges so the load synchronizes-with the producer and the pointed-to memory is visible before use. Signed-off-by: irozzo-1A <[email protected]>

leogr

Very good catch. The bug has been here since 2020.

The fix LGTM!

poiana · 2026-03-12T11:09:13Z

LGTM label has been added.

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Git tree hash: 93cab89060b1b4a4fc5f778a3895cb0d70ef92a7

leogr · 2026-03-12T11:09:23Z

/milestone 0.44.0

poiana · 2026-03-12T12:20:29Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: irozzo-1A, leogr, sgaist

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github-project-automation bot added this to Falco Roadmap Mar 12, 2026

github-project-automation bot moved this to Todo in Falco Roadmap Mar 12, 2026

poiana added release-note kind/bug dco-signoff: yes size/XS labels Mar 12, 2026

poiana requested review from Kaizhe and mstemm March 12, 2026 08:52

leogr approved these changes Mar 12, 2026

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poiana merged commit 8989870 into falcosecurity:master Mar 12, 2026
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fix(userspace/falco): fix watchdog race condition on timeout exchange#3820

fix(userspace/falco): fix watchdog race condition on timeout exchange#3820
poiana merged 1 commit intofalcosecurity:masterfrom
irozzo-1A:fix/watchdog-race-condition

irozzo-1A commented Mar 12, 2026 •

edited

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irozzo-1A commented Mar 12, 2026 •

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