[lldb-dev] Weird results running lldb under Valgrind

[Dmitry Antipov via lldb-dev]

On 9/25/20 5:53 PM, Dmitry Antipov wrote:

> On 9/24/20 9:14 PM, Greg Clayton wrote:
> 
>> This must be a valgrind issue, there would be major problems if the OS isn't able to lock mutex objects correctly ("mutex is locked simultaneously by two threads"). It is getting confused by a 
>> recursive mutex? LLDB uses recursive mutexes.
> 
> LLDB's Predicate.h uses plain std::mutex, which is not recursive, and std::lock_guard/std::unique_lock
> on top of it.
> 
> This needs more digging in because the latest Valgrind snapshot reports the same "impossible" condition.

To whom it may be interesting, thread sanitizer reports nearly the same:

WARNING: ThreadSanitizer: double lock of a mutex (pid=2049545)
     #0 pthread_mutex_lock <null> (libtsan.so.0+0x528ac)
     #1 __gthread_mutex_lock /usr/include/c++/10/x86_64-redhat-linux/bits/gthr-default.h:749 (liblldb.so.12git+0xd725c0)
     #2 std::mutex::lock() /usr/include/c++/10/bits/std_mutex.h:100 (liblldb.so.12git+0xd725c0)
     #3 std::lock_guard<std::mutex>::lock_guard(std::mutex&) /usr/include/c++/10/bits/std_mutex.h:159 (liblldb.so.12git+0xd725c0)
     #4 lldb_private::Predicate<bool>::SetValue(bool, lldb_private::PredicateBroadcastType) /home/antipov/llvm/source/lldb/include/lldb/Utility/Predicate.h:91 (liblldb.so.12git+0xd725c0)
     #5 lldb_private::EventDataReceipt::DoOnRemoval(lldb_private::Event*) /home/antipov/llvm/source/lldb/include/lldb/Utility/Event.h:121 (liblldb.so.12git+0xd725c0)
     #6 lldb_private::Event::DoOnRemoval() /home/antipov/llvm/source/lldb/source/Utility/Event.cpp:82 (liblldb.so.12git+0xedb7da)
     #7 lldb_private::Listener::FindNextEventInternal(std::unique_lock<std::mutex>&, lldb_private::Broadcaster*, lldb_private::ConstString const*, unsigned int, unsigned int, 
std::shared_ptr<lldb_private::Event>&, bool) /home/antipov/llvm/source/lldb/source/Utility/Listener.cpp:309 (liblldb.so.12git+0xee6099)
     #8 lldb_private::Listener::GetEventInternal(lldb_private::Timeout<std::ratio<1l, 1000000l> > const&, lldb_private::Broadcaster*, lldb_private::ConstString const*, unsigned int, unsigned int, 
std::shared_ptr<lldb_private::Event>&) /home/antipov/llvm/source/lldb/source/Utility/Listener.cpp:357 (liblldb.so.12git+0xee6b63)
     #9 lldb_private::Listener::GetEventForBroadcaster(lldb_private::Broadcaster*, std::shared_ptr<lldb_private::Event>&, lldb_private::Timeout<std::ratio<1l, 1000000l> > const&) 
/home/antipov/llvm/source/lldb/source/Utility/Listener.cpp:395 (liblldb.so.12git+0xee6dea)
     #10 lldb_private::Process::GetEventsPrivate(std::shared_ptr<lldb_private::Event>&, lldb_private::Timeout<std::ratio<1l, 1000000l> > const&, bool) 
/home/antipov/llvm/source/lldb/source/Target/Process.cpp:1139 (liblldb.so.12git+0xd7931d)
     #11 lldb_private::Process::RunPrivateStateThread(bool) /home/antipov/llvm/source/lldb/source/Target/Process.cpp:3872 (liblldb.so.12git+0xda3648)
     #12 lldb_private::Process::PrivateStateThread(void*) /home/antipov/llvm/source/lldb/source/Target/Process.cpp:3857 (liblldb.so.12git+0xda3f87)
     #13 lldb_private::HostNativeThreadBase::ThreadCreateTrampoline(void*) /home/antipov/llvm/source/lldb/source/Host/common/HostNativeThreadBase.cpp:68 (liblldb.so.12git+0xc2c0ea)
     #14 <null> <null> (libtsan.so.0+0x2d33f)

Again, lldb_private::Predicate uses plain std::mutex, which is not recursive.

Dmitry