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[3.14] gh-145615: Fix mimalloc page leak in the free-threaded build (gh-145626)#145691

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
Fixed a memory leak in the :term:`free-threaded build` where mimalloc pages
could become permanently unreclaimable until the owning thread exited.
5 changes: 4 additions & 1 deletionObjects/mimalloc/heap.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -100,7 +100,10 @@ static bool mi_heap_page_collect(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t
// note: this will free retired pages as well.
bool freed = _PyMem_mi_page_maybe_free(page, pq, collect >= MI_FORCE);
if (!freed && collect == MI_ABANDON) {
_mi_page_abandon(page, pq);
// _PyMem_mi_page_maybe_free may have moved the page to a different
// page queue, so we need to re-fetch the correct queue.
uint8_t bin = (mi_page_is_in_full(page) ? MI_BIN_FULL : _mi_bin(page->xblock_size));
_mi_page_abandon(page, &heap->pages[bin]);
}
}
else if (collect == MI_ABANDON) {
Expand Down
10 changes: 7 additions & 3 deletionsObjects/mimalloc/page.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -213,6 +213,13 @@ static void _mi_page_thread_free_collect(mi_page_t* page)

// update counts now
page->used -= count;

if (page->used == 0) {
// The page may have had a QSBR goal set from a previous point when it
// was all-free. That goal is no longer valid because the page was
// allocated from and then freed again by other threads.
_PyMem_mi_page_clear_qsbr(page);
}
}

void _mi_page_free_collect(mi_page_t* page, bool force) {
Expand All@@ -225,9 +232,6 @@ void _mi_page_free_collect(mi_page_t* page, bool force) {

// and the local free list
if (page->local_free != NULL) {
// any previous QSBR goals are no longer valid because we reused the page
_PyMem_mi_page_clear_qsbr(page);

if mi_likely(page->free == NULL) {
// usual case
page->free = page->local_free;
Expand Down
2 changes: 2 additions & 0 deletionsObjects/mimalloc/segment.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1286,6 +1286,7 @@ static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, s
_mi_stat_decrease(&tld->stats->pages_abandoned, 1);
#ifdef Py_GIL_DISABLED
page->qsbr_goal = 0;
mi_assert_internal(page->qsbr_node.next == NULL);
#endif
segment->abandoned--;
slice = mi_segment_page_clear(page, tld); // re-assign slice due to coalesce!
Expand DownExpand Up@@ -1361,6 +1362,7 @@ static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap,
// if everything free by now, free the page
#ifdef Py_GIL_DISABLED
page->qsbr_goal = 0;
mi_assert_internal(page->qsbr_node.next == NULL);
#endif
slice = mi_segment_page_clear(page, tld); // set slice again due to coalesceing
}
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31 changes: 25 additions & 6 deletionsObjects/obmalloc.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -149,6 +149,12 @@ should_advance_qsbr_for_page(struct _qsbr_thread_state *qsbr, mi_page_t *page)
}
return false;
}

static _PyThreadStateImpl *
tstate_from_heap(mi_heap_t *heap)
{
return _Py_CONTAINER_OF(heap->tld, _PyThreadStateImpl, mimalloc.tld);
}
#endif

static bool
Expand All@@ -157,23 +163,35 @@ _PyMem_mi_page_maybe_free(mi_page_t *page, mi_page_queue_t *pq, bool force)
#ifdef Py_GIL_DISABLED
assert(mi_page_all_free(page));
if (page->use_qsbr) {
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)PyThreadState_GET();
if (page->qsbr_goal != 0 && _Py_qbsr_goal_reached(tstate->qsbr, page->qsbr_goal)) {
struct _qsbr_thread_state *qsbr = ((_PyThreadStateImpl *)PyThreadState_GET())->qsbr;
if (page->qsbr_goal != 0 && _Py_qbsr_goal_reached(qsbr, page->qsbr_goal)) {
_PyMem_mi_page_clear_qsbr(page);
_mi_page_free(page, pq, force);
return true;
}

// gh-145615: since we are not freeing this page yet, we want to
// make it available for allocations. Note that the QSBR goal and
// linked list node remain set even if the page is later used for
// an allocation. We only detect and clear the QSBR goal when the
// page becomes empty again (used == 0).
if (mi_page_is_in_full(page)) {
_mi_page_unfull(page);
}

_PyMem_mi_page_clear_qsbr(page);
page->retire_expire = 0;

if (should_advance_qsbr_for_page(tstate->qsbr, page)) {
page->qsbr_goal = _Py_qsbr_advance(tstate->qsbr->shared);
if (should_advance_qsbr_for_page(qsbr, page)) {
page->qsbr_goal = _Py_qsbr_advance(qsbr->shared);
}
else {
page->qsbr_goal = _Py_qsbr_shared_next(tstate->qsbr->shared);
page->qsbr_goal = _Py_qsbr_shared_next(qsbr->shared);
}

// We may be freeing a page belonging to a different thread during a
// stop-the-world event. Find the _PyThreadStateImpl for the page.
_PyThreadStateImpl *tstate = tstate_from_heap(mi_page_heap(page));
llist_insert_tail(&tstate->mimalloc.page_list, &page->qsbr_node);
return false;
}
Expand All@@ -190,7 +208,8 @@ _PyMem_mi_page_reclaimed(mi_page_t *page)
if (page->qsbr_goal != 0) {
if (mi_page_all_free(page)) {
assert(page->qsbr_node.next == NULL);
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)PyThreadState_GET();
_PyThreadStateImpl *tstate = tstate_from_heap(mi_page_heap(page));
assert(tstate == (_PyThreadStateImpl *)_PyThreadState_GET());
page->retire_expire = 0;
llist_insert_tail(&tstate->mimalloc.page_list, &page->qsbr_node);
}
Expand Down
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