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author | Jonathan Wakely <jwakely@redhat.com> | 2023-01-05 16:23:51 +0000 |
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committer | Jonathan Wakely <jwakely@redhat.com> | 2023-01-06 11:52:01 +0000 |
commit | b9479ddc7a28fb672ca67304a67d66524d8200a4 (patch) | |
tree | af4a0762773b8393f3666b120317bb3338b02578 | |
parent | b990e80e39b41ec028d018eac7d2d040a537b681 (diff) | |
download | gcc-b9479ddc7a28fb672ca67304a67d66524d8200a4.zip gcc-b9479ddc7a28fb672ca67304a67d66524d8200a4.tar.gz gcc-b9479ddc7a28fb672ca67304a67d66524d8200a4.tar.bz2 |
libstdc++: Fix deadlock in debug iterator increment [PR108288]
With -fno-elide-constructors the debug iterator post-increment and
post-decrement operators are susceptible to deadlock. They take a mutex
lock and then return a temporary, which also attempts to take a lock to
attach itself to the sequence. If the return value and *this happen to
collide and use the same mutex from the pool, then you get a deadlock
trying to lock a mutex that is already held by the current thread.
The solution is to construct the return value before taking the lock.
The copy constructor and pre-inc/pre-dec operators already manage locks
correctly, without deadlock, so just implement post-inc/post-dec in the
conventional way, taking a copy then modifying *this, then returning the
copy.
libstdc++-v3/ChangeLog:
PR libstdc++/108288
* include/debug/safe_iterator.h (_Safe_iterator::operator++(int))
(_Safe_iterator::operator--(int)): Do not hold lock around
construction of return value.
-rw-r--r-- | libstdc++-v3/include/debug/safe_iterator.h | 18 |
1 files changed, 6 insertions, 12 deletions
diff --git a/libstdc++-v3/include/debug/safe_iterator.h b/libstdc++-v3/include/debug/safe_iterator.h index 117dc93..f9068ea 100644 --- a/libstdc++-v3/include/debug/safe_iterator.h +++ b/libstdc++-v3/include/debug/safe_iterator.h @@ -761,12 +761,9 @@ namespace __gnu_debug _Safe_iterator operator++(int) _GLIBCXX_NOEXCEPT { - _GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(), - _M_message(__msg_bad_inc) - ._M_iterator(*this, "this")); - __gnu_cxx::__scoped_lock __l(this->_M_get_mutex()); - return _Safe_iterator(this->base()++, this->_M_sequence, - _Attach_single()); + _Safe_iterator __ret = *this; + ++*this; + return __ret; } // ------ Bidirectional iterator requirements ------ @@ -788,12 +785,9 @@ namespace __gnu_debug _Safe_iterator operator--(int) _GLIBCXX_NOEXCEPT { - _GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(), - _M_message(__msg_bad_dec) - ._M_iterator(*this, "this")); - __gnu_cxx::__scoped_lock __l(this->_M_get_mutex()); - return _Safe_iterator(this->base()--, this->_M_sequence, - _Attach_single()); + _Safe_iterator __ret = *this; + --*this; + return __ret; } // ------ Random access iterator requirements ------ |