libstdc++ Enhance thread safety of debug mode iterators
Avoids race condition when checking for an iterator to be singular or to be comparable to another iterator. * src/c++/debug.cc (_Safe_sequence_base::_M_attach_single): Set attached iterator sequence pointer and version. (_Safe_sequence_base::_M_detach_single): Reset detached iterator. (_Safe_iterator_base::_M_attach): Remove attached iterator sequence pointer and version asignments. (_Safe_iterator_base::_M_attach_single): Likewise. (_Safe_iterator_base::_M_detach_single): Remove detached iterator reset. (_Safe_iterator_base::_M_singular): Use atomic load to access parent sequence. (_Safe_iterator_base::_M_can_compare): Likewise. (_Safe_iterator_base::_M_get_mutex): Likewise. (_Safe_local_iterator_base::_M_attach): Remove attached iterator container pointer and version assignments. (_Safe_local_iterator_base::_M_attach_single): Likewise. (_Safe_unordered_container_base::_M_attach_local_single): Set attached iterator container pointer and version. (_Safe_unordered_container_base::_M_detach_local_single): Reset detached iterator.
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@ -1,3 +1,26 @@
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2020-05-10 François Dumont <fdumont@gcc.gnu.org>
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* src/c++/debug.cc
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(_Safe_sequence_base::_M_attach_single): Set attached iterator
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sequence pointer and version.
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(_Safe_sequence_base::_M_detach_single): Reset detached iterator.
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(_Safe_iterator_base::_M_attach): Remove attached iterator sequence
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pointer and version asignments.
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(_Safe_iterator_base::_M_attach_single): Likewise.
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(_Safe_iterator_base::_M_detach_single): Remove detached iterator
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reset.
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(_Safe_iterator_base::_M_singular): Use atomic load to access parent
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sequence.
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(_Safe_iterator_base::_M_can_compare): Likewise.
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(_Safe_iterator_base::_M_get_mutex): Likewise.
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(_Safe_local_iterator_base::_M_attach): Remove attached iterator container
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pointer and version assignments.
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(_Safe_local_iterator_base::_M_attach_single): Likewise.
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(_Safe_unordered_container_base::_M_attach_local_single):Set attached
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iterator container pointer and version.
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(_Safe_unordered_container_base::_M_detach_local_single): Reset detached
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iterator.
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2020-05-07 Jonathan Wakely <jwakely@redhat.com>
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PR libstdc++/94971 (partial)
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@ -318,6 +318,8 @@ namespace __gnu_debug
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_Safe_sequence_base::
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_M_attach_single(_Safe_iterator_base* __it, bool __constant) throw ()
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{
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__it->_M_sequence = this;
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__it->_M_version = _M_version;
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_Safe_iterator_base*& __its =
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__constant ? _M_const_iterators : _M_iterators;
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__it->_M_next = __its;
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@ -345,6 +347,7 @@ namespace __gnu_debug
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_M_const_iterators = __it->_M_next;
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if (_M_iterators == __it)
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_M_iterators = __it->_M_next;
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__it->_M_reset();
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}
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void
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@ -355,11 +358,7 @@ namespace __gnu_debug
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// Attach to the new sequence (if there is one)
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if (__seq)
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{
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_M_sequence = __seq;
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_M_version = _M_sequence->_M_version;
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_M_sequence->_M_attach(this, __constant);
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}
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__seq->_M_attach(this, __constant);
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}
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void
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@ -370,11 +369,7 @@ namespace __gnu_debug
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// Attach to the new sequence (if there is one)
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if (__seq)
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{
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_M_sequence = __seq;
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_M_version = _M_sequence->_M_version;
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_M_sequence->_M_attach_single(this, __constant);
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}
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__seq->_M_attach_single(this, __constant);
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}
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void
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@ -400,10 +395,7 @@ namespace __gnu_debug
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_M_detach_single() throw ()
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{
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if (_M_sequence)
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{
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_M_sequence->_M_detach_single(this);
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_M_reset();
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}
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_M_sequence->_M_detach_single(this);
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}
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void
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@ -419,20 +411,32 @@ namespace __gnu_debug
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bool
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_Safe_iterator_base::
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_M_singular() const throw ()
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{ return !_M_sequence || _M_version != _M_sequence->_M_version; }
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{
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auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
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return !seq || _M_version != seq->_M_version;
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}
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bool
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_Safe_iterator_base::
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_M_can_compare(const _Safe_iterator_base& __x) const throw ()
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{
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return (!_M_singular()
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&& !__x._M_singular() && _M_sequence == __x._M_sequence);
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auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
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if (seq && _M_version == seq->_M_version)
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{
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auto xseq = __atomic_load_n(&__x._M_sequence, __ATOMIC_ACQUIRE);
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return xseq && __x._M_version == xseq->_M_version && seq == xseq;
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}
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return false;
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}
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__gnu_cxx::__mutex&
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_Safe_iterator_base::
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_M_get_mutex() throw ()
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{ return _M_sequence->_M_get_mutex(); }
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{
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auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
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return get_safe_base_mutex(seq);
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}
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_Safe_unordered_container_base*
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_Safe_local_iterator_base::
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@ -447,11 +451,8 @@ namespace __gnu_debug
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// Attach to the new container (if there is one)
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if (__cont)
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{
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_M_sequence = __cont;
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_M_version = _M_sequence->_M_version;
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_M_get_container()->_M_attach_local(this, __constant);
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}
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static_cast<_Safe_unordered_container_base*>(__cont)
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->_M_attach_local(this, __constant);
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}
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void
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@ -462,11 +463,8 @@ namespace __gnu_debug
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// Attach to the new container (if there is one)
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if (__cont)
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{
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_M_sequence = __cont;
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_M_version = _M_sequence->_M_version;
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_M_get_container()->_M_attach_local_single(this, __constant);
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}
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static_cast<_Safe_unordered_container_base*>(__cont)
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->_M_attach_local_single(this, __constant);
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}
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void
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@ -526,6 +524,8 @@ namespace __gnu_debug
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_Safe_unordered_container_base::
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_M_attach_local_single(_Safe_iterator_base* __it, bool __constant) throw ()
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{
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__it->_M_sequence = this;
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__it->_M_version = _M_version;
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_Safe_iterator_base*& __its =
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__constant ? _M_const_local_iterators : _M_local_iterators;
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__it->_M_next = __its;
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@ -553,6 +553,7 @@ namespace __gnu_debug
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_M_const_local_iterators = __it->_M_next;
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if (_M_local_iterators == __it)
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_M_local_iterators = __it->_M_next;
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__it->_M_reset();
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}
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}
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