[Bug sanitizer/64337] New: ThreadSanitizer: std::thread + lambda false positive

["p.bartosiewi at partner dot samsung.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64337

            Bug ID: 64337
           Summary: ThreadSanitizer: std::thread + lambda false positive
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: p.bartosiewi at partner dot samsung.com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org

I think this is a false positive tsan warning:

$ cat tsan.cpp 
#include <thread>
#include <cstdio>

int main() {
    int str = 5;
    auto f = [=] {
        printf("str: %d\n", str);
    };
    std::thread t(f);
    t.join();
}

$ g++ --version
g++ (GCC) 4.9.2 20141101 (Red Hat 4.9.2-1)

$ ./a.out 
str: 5
==================
WARNING: ThreadSanitizer: data race (pid=21079)
  Write of size 8 at 0x7d0c0000efd8 by thread T1:
    #0 operator delete(void*) <null>:0 (libtsan.so.0+0x00000004c8c0)
    #1 deallocate /usr/include/c++/4.9.2/ext/new_allocator.h:110
(a.out+0x0000000020ed)
    #2 deallocate /usr/include/c++/4.9.2/bits/alloc_traits.h:383
(a.out+0x000000001fdc)
    #3 _M_destroy /usr/include/c++/4.9.2/bits/shared_ptr_base.h:535
(a.out+0x000000002758)
    #4 <null> <null>:0 (libstdc++.so.6+0x0000000bae11)

  Previous atomic write of size 4 at 0x7d0c0000efd8 by main thread:
    #0 __tsan_atomic32_fetch_add <null>:0 (libtsan.so.0+0x000000020a7e)
    #1 __exchange_and_add /usr/include/c++/4.9.2/ext/atomicity.h:49
(a.out+0x0000000014b0)
    #2 __exchange_and_add_dispatch /usr/include/c++/4.9.2/ext/atomicity.h:82
(a.out+0x000000001567)
    #3 std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release()
/usr/include/c++/4.9.2/bits/shared_ptr_base.h:146 (a.out+0x000000002d4f)
    #4 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count()
/usr/include/c++/4.9.2/bits/shared_ptr_base.h:666 (a.out+0x000000002d1a)
    #5 std::__shared_ptr<std::thread::_Impl_base,
(__gnu_cxx::_Lock_policy)2>::~__shared_ptr()
/usr/include/c++/4.9.2/bits/shared_ptr_base.h:914 (a.out+0x000000002c25)
    #6 std::shared_ptr<std::thread::_Impl_base>::~shared_ptr()
/usr/include/c++/4.9.2/bits/shared_ptr.h:93 (a.out+0x000000002c51)
    #7 thread<main()::<lambda()>&> /usr/include/c++/4.9.2/thread:135
(a.out+0x000000001747)
    #8 main tsan.cpp:11 (a.out+0x000000001606)

  Location is heap block of size 48 at 0x7d0c0000efd0 allocated by main thread:
    #0 operator new(unsigned long) <null>:0 (libtsan.so.0+0x00000004cb42)
    #1 allocate /usr/include/c++/4.9.2/ext/new_allocator.h:104
(a.out+0x00000000204d)
    #2 allocate /usr/include/c++/4.9.2/bits/alloc_traits.h:357
(a.out+0x000000001f31)
    #3
__shared_count<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()> >,
std::allocator<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()> > >,
std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/bits/shared_ptr_base.h:616 (a.out+0x000000001dfd)
    #4
__shared_ptr<std::allocator<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()>
> >, std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/bits/shared_ptr_base.h:1090 (a.out+0x000000001d2f)
    #5
shared_ptr<std::allocator<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()>
> >, std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/bits/shared_ptr.h:316 (a.out+0x000000001cc3)
    #6
allocate_shared<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()> >,
std::allocator<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()> > >,
std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/bits/shared_ptr.h:588 (a.out+0x000000001c54)
    #7 make_shared<std::thread::_Impl<std::_Bind_simple<main()::<lambda()>()>
>, std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/bits/shared_ptr.h:604 (a.out+0x000000001b15)
    #8 _M_make_routine<std::_Bind_simple<main()::<lambda()>()> >
/usr/include/c++/4.9.2/thread:193 (a.out+0x000000001995)
    #9 thread<main()::<lambda()>&> /usr/include/c++/4.9.2/thread:135
(a.out+0x000000001715)
    #10 main tsan.cpp:11 (a.out+0x000000001606)

  Thread T1 (tid=21081, running) created by main thread at:
    #0 pthread_create <null>:0 (libtsan.so.0+0x00000004ac26)
    #1 std::thread::_M_start_thread(std::shared_ptr<std::thread::_Impl_base>)
<null>:0 (libstdc++.so.6+0x0000000baed8)
    #2 main tsan.cpp:11 (a.out+0x000000001606)

SUMMARY: ThreadSanitizer: data race ??:0 operator delete(void*)
==================
ThreadSanitizer: reported 1 warnings