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Fix #8335: Race condition in music mixer #9450

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merged 1 commit into from Jul 21, 2021

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@LordAro LordAro commented Jul 19, 2021

Motivation / Problem

#8335

Description

Basic. Add a mutex around all _music_stream accesses.
Also removes some '\r' from the file. (Commit checker should probably check for this?)

Limitations

Might be too simplistic of a fix, IDK. There's a remaining race condition in mixer.cpp due to _setting_client accesses.

WARNING: ThreadSanitizer: data race (pid=116977)
  Write of size 1 at 0x556b0ff4cfae by thread T4 (mutexes: write M1050):
    #0 WriteValue(void*, unsigned int, long long) /home/lordaro/dev/OTTD/openttd/src/saveload/saveload.cpp:833 (openttd+0xafcb01)
    #1 IntSettingDesc::Write(void const*, int) const /home/lordaro/dev/OTTD/openttd/src/settings.cpp:505 (openttd+0xfbad60)
    #2 IntSettingDesc::MakeValueValidAndWrite(void const*, int) const /home/lordaro/dev/OTTD/openttd/src/settings.cpp:437 (openttd+0xfba932)
    #3 IntSettingDesc::ParseValue(IniItem const*, void*) const /home/lordaro/dev/OTTD/openttd/src/settings.cpp:606 (openttd+0xfbb5ca)
    #4 IniLoadSettings /home/lordaro/dev/OTTD/openttd/src/settings.cpp:599 (openttd+0xfbb433)
    #5 HandleSettingDescs /home/lordaro/dev/OTTD/openttd/src/settings.cpp:1153 (openttd+0xfbeb97)
    #6 LoadFromConfig(bool) /home/lordaro/dev/OTTD/openttd/src/settings.cpp:1216 (openttd+0xfbf073)
    #7 AfterNewGRFScan::OnNewGRFsScanned() /home/lordaro/dev/OTTD/openttd/src/openttd.cpp:434 (openttd+0xf2661e)
    #8 DoScanNewGRFFiles(NewGRFScanCallback*) /home/lordaro/dev/OTTD/openttd/src/newgrf_config.cpp:707 (openttd+0xe87859)
    #9 ScanNewGRFFiles(NewGRFScanCallback*) /home/lordaro/dev/OTTD/openttd/src/newgrf_config.cpp:725 (openttd+0xe87914)
    #10 GameLoop() /home/lordaro/dev/OTTD/openttd/src/openttd.cpp:1426 (openttd+0xf23db1)
    #11 VideoDriver::GameLoop() /home/lordaro/dev/OTTD/openttd/src/video/video_driver.cpp:37 (openttd+0xbbbef6)
    #12 VideoDriver::GameThread() /home/lordaro/dev/OTTD/openttd/src/video/video_driver.cpp:44 (openttd+0xbbbf7f)
    #13 VideoDriver::GameThreadThunk(VideoDriver*) /home/lordaro/dev/OTTD/openttd/src/video/video_driver.cpp:81 (openttd+0xbbc12e)
    #14 StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&)(VideoDriver*), VideoDriver*&&)#1}::operator()(char const*, void (*&&)(VideoDriver*), VideoDriver*&&) const /home/lordaro/dev/OTTD/openttd/src/video/../thread.h:65 (openttd+0xbbd8e5)
    #15 void std::__invoke_impl<void, StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&)(VideoDriver*), VideoDriver*&&)#1}, char const*, void (*)(VideoDriver*), VideoDriver*>(std::__invoke_other, StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&&&)(VideoDriver*), VideoDriver*&&)#1}, char const*&&, void (*&&)(VideoDriver*), VideoDriver*&&) /usr/include/c++/11.1.0/bits/invoke.h:61 (openttd+0xbbeacc)
    #16 _ZSt8__invokeIZ14StartNewThreadIPFvP11VideoDriverEJS2_EEbPSt6threadPKcOT_DpOT0_EUlS8_OS4_OS2_E_JS8_S4_S2_EENSt15__invoke_resultIS9_JDpSB_EE4typeESA_SD_ /usr/include/c++/11.1.0/bits/invoke.h:96 (openttd+0xbbe91d)
    #17 void std::thread::_Invoker<std::tuple<StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&)(VideoDriver*), VideoDriver*&&)#1}, char const*, void (*)(VideoDriver*), VideoDriver*> >::_M_invoke<0ul, 1ul, 2ul, 3ul>(std::_Index_tuple<0ul, 1ul, 2ul, 3ul>) /usr/include/c++/11.1.0/bits/std_thread.h:253 (openttd+0xbbe77a)
    #18 std::thread::_Invoker<std::tuple<StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&)(VideoDriver*), VideoDriver*&&)#1}, char const*, void (*)(VideoDriver*), VideoDriver*> >::operator()() /usr/include/c++/11.1.0/bits/std_thread.h:260 (openttd+0xbbe6d2)
    #19 std::thread::_State_impl<std::thread::_Invoker<std::tuple<StartNewThread<void (*)(VideoDriver*), VideoDriver*>(std::thread*, char const*, void (*&&)(VideoDriver*), VideoDriver*&&)::{lambda(char const*, void (*&&)(VideoDriver*), VideoDriver*&&)#1}, char const*, void (*)(VideoDriver*), VideoDriver*> > >::_M_run() /usr/include/c++/11.1.0/bits/std_thread.h:211 (openttd+0xbbe68c)
    #20 execute_native_thread_routine /build/gcc/src/gcc/libstdc++-v3/src/c++11/thread.cc:82 (libstdc++.so.6+0xd33c3)

  Previous read of size 1 at 0x556b0ff4cfae by thread T2 (mutexes: write M923):
    #0 MxMixSamples(void*, unsigned int) /home/lordaro/dev/OTTD/openttd/src/mixer.cpp:167 (openttd+0xdeff32)
    #1 fill_sound_buffer /home/lordaro/dev/OTTD/openttd/src/sound/sdl2_s.cpp:31 (openttd+0xb99abd)
    #2 <null> <null> (libSDL2-2.0.so.0+0x23a9f)

  Location is global '_settings_client' of size 648 at 0x556b0ff4cd80 (openttd+0x000003701fae)

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

  • The bug fix is important enough to be backported? (label: 'backport requested')
  • This PR affects the save game format? (label 'savegame upgrade')
  • This PR affects the GS/AI API? (label 'needs review: Script API')
    • ai_changelog.hpp, gs_changelog.hpp need updating.
    • The compatibility wrappers (compat_*.nut) need updating.
  • This PR affects the NewGRF API? (label 'needs review: NewGRF')
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@rubidium42 rubidium42 left a comment

I've got no other idea how to prevent _music_stream from being made nullptr between the check and call, so I guess this is good enough for that.

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@LordAro LordAro merged commit 6c33b4e into OpenTTD:master Jul 21, 2021
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@LordAro LordAro deleted the music-stream-race branch Jul 21, 2021
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2 participants