From 0b83c4fabb899fdbb3ae60ed75b7004b7859fae9 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Fran=C3=A7ois=20Dumont?= Date: Sat, 29 Feb 2020 18:22:55 +0100 Subject: [PATCH] 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. --- libstdc++-v3/ChangeLog | 23 +++++++++++++ libstdc++-v3/src/c++11/debug.cc | 57 +++++++++++++++++---------------- 2 files changed, 52 insertions(+), 28 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index a2ff49d9e51..8fb6b86474b 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,26 @@ +2020-05-10 François Dumont + + * 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. + 2020-05-07 Jonathan Wakely PR libstdc++/94971 (partial) diff --git a/libstdc++-v3/src/c++11/debug.cc b/libstdc++-v3/src/c++11/debug.cc index 18da9da9c52..032e0b50b91 100644 --- a/libstdc++-v3/src/c++11/debug.cc +++ b/libstdc++-v3/src/c++11/debug.cc @@ -318,6 +318,8 @@ namespace __gnu_debug _Safe_sequence_base:: _M_attach_single(_Safe_iterator_base* __it, bool __constant) throw () { + __it->_M_sequence = this; + __it->_M_version = _M_version; _Safe_iterator_base*& __its = __constant ? _M_const_iterators : _M_iterators; __it->_M_next = __its; @@ -345,6 +347,7 @@ namespace __gnu_debug _M_const_iterators = __it->_M_next; if (_M_iterators == __it) _M_iterators = __it->_M_next; + __it->_M_reset(); } void @@ -355,11 +358,7 @@ namespace __gnu_debug // Attach to the new sequence (if there is one) if (__seq) - { - _M_sequence = __seq; - _M_version = _M_sequence->_M_version; - _M_sequence->_M_attach(this, __constant); - } + __seq->_M_attach(this, __constant); } void @@ -370,11 +369,7 @@ namespace __gnu_debug // Attach to the new sequence (if there is one) if (__seq) - { - _M_sequence = __seq; - _M_version = _M_sequence->_M_version; - _M_sequence->_M_attach_single(this, __constant); - } + __seq->_M_attach_single(this, __constant); } void @@ -400,10 +395,7 @@ namespace __gnu_debug _M_detach_single() throw () { if (_M_sequence) - { - _M_sequence->_M_detach_single(this); - _M_reset(); - } + _M_sequence->_M_detach_single(this); } void @@ -419,20 +411,32 @@ namespace __gnu_debug bool _Safe_iterator_base:: _M_singular() const throw () - { return !_M_sequence || _M_version != _M_sequence->_M_version; } + { + auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE); + return !seq || _M_version != seq->_M_version; + } bool _Safe_iterator_base:: _M_can_compare(const _Safe_iterator_base& __x) const throw () { - return (!_M_singular() - && !__x._M_singular() && _M_sequence == __x._M_sequence); + auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE); + if (seq && _M_version == seq->_M_version) + { + auto xseq = __atomic_load_n(&__x._M_sequence, __ATOMIC_ACQUIRE); + return xseq && __x._M_version == xseq->_M_version && seq == xseq; + } + + return false; } __gnu_cxx::__mutex& _Safe_iterator_base:: _M_get_mutex() throw () - { return _M_sequence->_M_get_mutex(); } + { + auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE); + return get_safe_base_mutex(seq); + } _Safe_unordered_container_base* _Safe_local_iterator_base:: @@ -447,11 +451,8 @@ namespace __gnu_debug // Attach to the new container (if there is one) if (__cont) - { - _M_sequence = __cont; - _M_version = _M_sequence->_M_version; - _M_get_container()->_M_attach_local(this, __constant); - } + static_cast<_Safe_unordered_container_base*>(__cont) + ->_M_attach_local(this, __constant); } void @@ -462,11 +463,8 @@ namespace __gnu_debug // Attach to the new container (if there is one) if (__cont) - { - _M_sequence = __cont; - _M_version = _M_sequence->_M_version; - _M_get_container()->_M_attach_local_single(this, __constant); - } + static_cast<_Safe_unordered_container_base*>(__cont) + ->_M_attach_local_single(this, __constant); } void @@ -526,6 +524,8 @@ namespace __gnu_debug _Safe_unordered_container_base:: _M_attach_local_single(_Safe_iterator_base* __it, bool __constant) throw () { + __it->_M_sequence = this; + __it->_M_version = _M_version; _Safe_iterator_base*& __its = __constant ? _M_const_local_iterators : _M_local_iterators; __it->_M_next = __its; @@ -553,6 +553,7 @@ namespace __gnu_debug _M_const_local_iterators = __it->_M_next; if (_M_local_iterators == __it) _M_local_iterators = __it->_M_next; + __it->_M_reset(); } } -- 2.30.2