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re PR libstdc++/24469 (Possible race condition in mt_allocator causing SIGSEGV) 

2006-09-02  Paolo Carlini  <pcarlini@suse.de>
	    Richard Guenther  <rguenther@suse.de>

	PR libstdc++/24469
	* src/mt_allocator.cc (__pool<true>::_M_reserve_block,
	__pool<true>::_M_reclaim_block): Fix the logic to avoid
	races, exploit atomic counters stored in second part of
	the memory pointed by _M_used.
	(__pool<true>::_M_initialize): Adjust _M_used allocation.
	* include/ext/mt_allocator.h (__pool<true>::_Bin_record):
	Update comment.

Co-Authored-By: Richard Guenther <rguenther@suse.de>

From-SVN: r116660
This commit is contained in:
Paolo Carlini 2006-09-02 08:31:45 +00:00 committed by Paolo Carlini
parent b73aec4fa5
commit 1d3e6248e5
3 changed files with 73 additions and 26 deletions
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12
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,15 @@
2006-09-02 Paolo Carlini <pcarlini@suse.de>
Richard Guenther <rguenther@suse.de>
PR libstdc++/24469
* src/mt_allocator.cc (__pool<true>::_M_reserve_block,
__pool<true>::_M_reclaim_block): Fix the logic to avoid
races, exploit atomic counters stored in second part of
the memory pointed by _M_used.
(__pool<true>::_M_initialize): Adjust _M_used allocation.
* include/ext/mt_allocator.h (__pool<true>::_Bin_record):
Update comment.
2006-08-31 Benjamin Kosnik <bkoz@redhat.com>
PR libstdc++/28671 continued

9
libstdc++-v3/include/ext/mt_allocator.h
View File

@ -298,8 +298,13 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
// An "array" of counters used to keep track of the amount of
// blocks that are on the freelist/used for each thread id.
// Memory to these "arrays" is allocated in _S_initialize() for
// _S_max_threads + global pool 0.
// - Note that the second part of the allocated _M_used "array"
// actually hosts (atomic) counters of reclaimed blocks: in
// _M_reserve_block and in _M_reclaim_block those numbers are
// subtracted from the first ones to obtain the actual size
// of the "working set" of the given thread.
// - Memory to these "arrays" is allocated in _S_initialize()
// for _S_max_threads + global pool 0.
size_t* _M_free;
size_t* _M_used;

78
libstdc++-v3/src/mt_allocator.cc
View File

@ -34,6 +34,7 @@
#include <bits/c++config.h>
#include <bits/concurrence.h>
#include <ext/mt_allocator.h>
#include <cstring>
namespace
{
@ -263,13 +264,33 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
// number of records is "high enough".
const size_t __thread_id = _M_get_thread_id();
const _Tune& __options = _M_get_options();
const unsigned long __limit = 100 * (_M_bin_size - __which)
* __options._M_freelist_headroom;
const size_t __limit = (100 * (_M_bin_size - __which)
* __options._M_freelist_headroom);
unsigned long __remove = __bin._M_free[__thread_id];
size_t __remove = __bin._M_free[__thread_id];
__remove *= __options._M_freelist_headroom;
if (__remove >= __bin._M_used[__thread_id])
__remove -= __bin._M_used[__thread_id];
// NB: We assume that reads of _Atomic_words are atomic.
const size_t __max_threads = __options._M_max_threads + 1;
_Atomic_word* const __reclaimed_base =
reinterpret_cast<_Atomic_word*>(__bin._M_used + __max_threads);
const _Atomic_word __reclaimed = __reclaimed_base[__thread_id];
const size_t __used = __bin._M_used[__thread_id] - __reclaimed;
// NB: For performance sake we don't resync every time, in order
// to spare atomic ops. Note that if __reclaimed increased by,
// say, 1024, since the last sync, it means that the other
// threads executed the atomic in the else below at least the
// same number of times (at least, because _M_reserve_block may
// have decreased the counter), therefore one more cannot hurt.
if (__reclaimed > 1024)
{
__bin._M_used[__thread_id] -= __reclaimed;
__atomic_add(&__reclaimed_base[__thread_id], -__reclaimed);
}
if (__remove >= __used)
__remove -= __used;
else
__remove = 0;
if (__remove > __limit && __remove > __bin._M_free[__thread_id])
@ -277,7 +298,7 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
_Block_record* __first = __bin._M_first[__thread_id];
_Block_record* __tmp = __first;
__remove /= __options._M_freelist_headroom;
const unsigned long __removed = __remove;
const size_t __removed = __remove;
while (--__remove > 0)
__tmp = __tmp->_M_next;
__bin._M_first[__thread_id] = __tmp->_M_next;
@ -292,8 +313,11 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
// Return this block to our list and update counters and
// owner id as needed.
--__bin._M_used[__block->_M_thread_id];
if (__block->_M_thread_id == __thread_id)
--__bin._M_used[__thread_id];
else
__atomic_add(&__reclaimed_base[__block->_M_thread_id], 1);
__block->_M_next = __bin._M_first[__thread_id];
__bin._M_first[__thread_id] = __block;
@ -333,6 +357,14 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
_Block_record* __block = NULL;
if (__gthread_active_p())
{
// Resync the _M_used counters.
const size_t __max_threads = __options._M_max_threads + 1;
_Atomic_word* const __reclaimed_base =
reinterpret_cast<_Atomic_word*>(__bin._M_used + __max_threads);
const _Atomic_word __reclaimed = __reclaimed_base[__thread_id];
__bin._M_used[__thread_id] -= __reclaimed;
__atomic_add(&__reclaimed_base[__thread_id], -__reclaimed);
__gthread_mutex_lock(__bin._M_mutex);
if (__bin._M_first[0] == NULL)
{
@ -533,14 +565,19 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
{
_Bin_record& __bin = _M_bin[__n];
__v = ::operator new(sizeof(_Block_record*) * __max_threads);
std::memset(__v, 0, sizeof(_Block_record*) * __max_threads);
__bin._M_first = static_cast<_Block_record**>(__v);
__bin._M_address = NULL;
__v = ::operator new(sizeof(size_t) * __max_threads);
std::memset(__v, 0, sizeof(size_t) * __max_threads);
__bin._M_free = static_cast<size_t*>(__v);
__v = ::operator new(sizeof(size_t) * __max_threads);
__v = ::operator new(sizeof(size_t) * __max_threads
+ sizeof(_Atomic_word) * __max_threads);
std::memset(__v, 0, (sizeof(size_t) * __max_threads
+ sizeof(_Atomic_word) * __max_threads));
__bin._M_used = static_cast<size_t*>(__v);
__v = ::operator new(sizeof(__gthread_mutex_t));
@ -555,12 +592,6 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
#else
{ __GTHREAD_MUTEX_INIT_FUNCTION(__bin._M_mutex); }
#endif
for (size_t __threadn = 0; __threadn < __max_threads; ++__threadn)
{
__bin._M_first[__threadn] = NULL;
__bin._M_free[__threadn] = 0;
__bin._M_used[__threadn] = 0;
}
}
}
else
@ -729,16 +760,21 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
{
_Bin_record& __bin = _M_bin[__n];
__v = ::operator new(sizeof(_Block_record*) * __max_threads);
std::memset(__v, 0, sizeof(_Block_record*) * __max_threads);
__bin._M_first = static_cast<_Block_record**>(__v);
__bin._M_address = NULL;
__v = ::operator new(sizeof(size_t) * __max_threads);
std::memset(__v, 0, sizeof(size_t) * __max_threads);
__bin._M_free = static_cast<size_t*>(__v);
__v = ::operator new(sizeof(size_t) * __max_threads);
__v = ::operator new(sizeof(size_t) * __max_threads +
sizeof(_Atomic_word) * __max_threads);
std::memset(__v, 0, (sizeof(size_t) * __max_threads
+ sizeof(_Atomic_word) * __max_threads));
__bin._M_used = static_cast<size_t*>(__v);
__v = ::operator new(sizeof(__gthread_mutex_t));
__bin._M_mutex = static_cast<__gthread_mutex_t*>(__v);
@ -751,12 +787,6 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
#else
{ __GTHREAD_MUTEX_INIT_FUNCTION(__bin._M_mutex); }
#endif
for (size_t __threadn = 0; __threadn < __max_threads; ++__threadn)
{
__bin._M_first[__threadn] = NULL;
__bin._M_free[__threadn] = 0;
__bin._M_used[__threadn] = 0;
}
}
}
else