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ensure forced abandoned pages can be accessed after free

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daanx
2024-11-25 18:41:57 -08:00
parent 9b7ac9a1a6
commit 7673aa2517
3 changed files with 26 additions and 21 deletions
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38
src/segment.c
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@@ -652,6 +652,10 @@ static mi_segment_t* mi_segment_alloc(size_t required, mi_page_kind_t page_kind,
static void mi_segment_free(mi_segment_t* segment, bool force, mi_segments_tld_t* tld) {
MI_UNUSED(force);
mi_assert(segment != NULL);
// in `mi_segment_force_abandon` we set this to true to ensure the segment's memory stays valid
if (segment->dont_free) return;
// don't purge as we are freeing now
mi_segment_remove_all_purges(segment, false /* don't force as we are about to free */, tld);
mi_segment_remove_from_free_queue(segment, tld);
@@ -1056,32 +1060,34 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t block_size,
static void mi_segment_force_abandon(mi_segment_t* segment, mi_segments_tld_t* tld)
{
mi_assert_internal(segment->abandoned < segment->used);
mi_assert_internal(!segment->dont_free);
// ensure the segment does not get free'd underneath us (so we can check if a page has been freed in `mi_page_force_abandon`)
segment->dont_free = true;
// for all pages
for (size_t i = 0; i < segment->capacity; i++) {
mi_page_t* page = &segment->pages[i];
if (page->segment_in_use) {
// ensure used count is up to date and collect potential concurrent frees
_mi_page_free_collect(page, false);
{
// abandon the page if it is still in-use (this will free it if possible as well)
mi_assert_internal(segment->used > 0);
if (segment->used == segment->abandoned+1) {
// the last page.. abandon and return as the segment will be abandoned after this
// and we should no longer access it.
_mi_page_force_abandon(page);
return;
}
else {
// abandon and continue
_mi_page_force_abandon(page);
}
// abandon the page if it is still in-use (this will free the page if possible as well (but not our segment))
mi_assert_internal(segment->used > 0);
if (segment->used == segment->abandoned+1) {
// the last page.. abandon and return as the segment will be abandoned after this
// and we should no longer access it.
segment->dont_free = false;
_mi_page_force_abandon(page);
return;
}
else {
// abandon and continue
_mi_page_force_abandon(page);
}
}
}
segment->dont_free = false;
mi_assert(segment->used == segment->abandoned);
mi_assert(segment->used == 0);
if (segment->used == 0) {
if (segment->used == 0) { // paranoia
// all free now
mi_segment_free(segment, false, tld);
}