[Bug #18014] Fix memory leak in GC when using Ractors

When a Ractor is removed, the freelist in the Ractor cache is not
returned to the GC, leaving the freelist permanently lost. This commit
recycles the freelist when the Ractor is destroyed, preventing a memory
leak from occurring.

4 files changed, 64 insertions, 66 deletions

diff --git a/gc.c b/gc.c
index c7e3034240..9af83de055 100644
--- a/gc.c
+++ b/gc.c
@@ -1817,45 +1817,34 @@ heap_page_add_freeobj(rb_objspace_t *objspace, struct heap_page *page, VALUE obj
     gc_report(3, objspace, "heap_page_add_freeobj: add %p to freelist\n", (void *)obj);
 }
 
-static inline bool
+static inline void
 heap_add_freepage(rb_heap_t *heap, struct heap_page *page)
 {
     asan_unpoison_memory_region(&page->freelist, sizeof(RVALUE*), false);
     GC_ASSERT(page->free_slots != 0);
+    GC_ASSERT(page->freelist != NULL);
 
-    if (page->freelist) {
-        page->free_next = heap->free_pages;
-        heap->free_pages = page;
+    page->free_next = heap->free_pages;
+    heap->free_pages = page;
 
-        RUBY_DEBUG_LOG("page:%p freelist:%p", page, page->freelist);
+    RUBY_DEBUG_LOG("page:%p freelist:%p", page, page->freelist);
 
-        asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
-        return true;
-    }
-    else {
-        asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
-        return false;
-    }
+    asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
 }
 
 #if GC_ENABLE_INCREMENTAL_MARK
-static inline int
+static inline void
 heap_add_poolpage(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *page)
 {
     asan_unpoison_memory_region(&page->freelist, sizeof(RVALUE*), false);
-    if (page->freelist) {
-	page->free_next = heap->pooled_pages;
-	heap->pooled_pages = page;
-	objspace->rincgc.pooled_slots += page->free_slots;
-        asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
+    GC_ASSERT(page->free_slots != 0);
+    GC_ASSERT(page->freelist != NULL);
 
-	return TRUE;
-    }
-    else {
-        asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
+    page->free_next = heap->pooled_pages;
+    heap->pooled_pages = page;
+    objspace->rincgc.pooled_slots += page->free_slots;
 
-	return FALSE;
-    }
+    asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
 }
 #endif
 
@@ -2317,7 +2306,7 @@ rvargc_find_contiguous_slots(int slots, RVALUE *freelist)
 }
 #endif
 
-static inline bool heap_add_freepage(rb_heap_t *heap, struct heap_page *page);
+static inline void heap_add_freepage(rb_heap_t *heap, struct heap_page *page);
 static struct heap_page * heap_next_freepage(rb_objspace_t *objspace, rb_heap_t *heap);
 static inline void ractor_set_cache(rb_ractor_t *cr, struct heap_page *page);
 
@@ -5563,32 +5552,7 @@ gc_sweep_start(rb_objspace_t *objspace)
 
     rb_ractor_t *r = NULL;
     list_for_each(&GET_VM()->ractor.set, r, vmlr_node) {
-        struct heap_page *page = r->newobj_cache.using_page;
-        RVALUE *freelist = r->newobj_cache.freelist;
-        RUBY_DEBUG_LOG("ractor using_page:%p freelist:%p", page, freelist);
-
-        if (page && freelist) {
-            asan_unpoison_memory_region(&page->freelist, sizeof(RVALUE*), false);
-            if (page->freelist) {
-                RVALUE *p = page->freelist;
-                asan_unpoison_object((VALUE)p, false);
-                while (p->as.free.next) {
-                    RVALUE *prev = p;
-                    p = p->as.free.next;
-                    asan_poison_object((VALUE)prev);
-                    asan_unpoison_object((VALUE)p, false);
-                }
-                p->as.free.next = freelist;
-                asan_poison_object((VALUE)p);
-            }
-            else {
-                page->freelist = freelist;
-            }
-            asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
-        }
-
-        r->newobj_cache.using_page = NULL;
-        r->newobj_cache.freelist = NULL;
+        rb_gc_ractor_newobj_cache_clear(&r->newobj_cache);
     }
 }
 
@@ -5651,22 +5615,19 @@ gc_sweep_step(rb_objspace_t *objspace, rb_heap_t *heap)
 	else if (free_slots > 0) {
 #if GC_ENABLE_INCREMENTAL_MARK
 	    if (need_pool) {
-		if (heap_add_poolpage(objspace, heap, sweep_page)) {
-		    need_pool = FALSE;
-		}
+                heap_add_poolpage(objspace, heap, sweep_page);
+                need_pool = FALSE;
 	    }
 	    else {
-                if (heap_add_freepage(heap, sweep_page)) {
-                    swept_slots += free_slots;
-                    if (swept_slots > 2048) {
-                        break;
-                    }
+                heap_add_freepage(heap, sweep_page);
+                swept_slots += free_slots;
+                if (swept_slots > 2048) {
+                    break;
                 }
 	    }
 #else
-            if (heap_add_freepage(heap, sweep_page)) {
-                break;
-            }
+            heap_add_freepage(heap, sweep_page);
+            break;
 #endif
 	}
 	else {
@@ -8643,6 +8604,37 @@ rb_obj_gc_flags(VALUE obj, ID* flags, size_t max)
 /* GC */
 
 void
+rb_gc_ractor_newobj_cache_clear(rb_ractor_newobj_cache_t *newobj_cache)
+{
+    struct heap_page *page = newobj_cache->using_page;
+    RVALUE *freelist = newobj_cache->freelist;
+    RUBY_DEBUG_LOG("ractor using_page:%p freelist:%p", page, freelist);
+
+    if (page && freelist) {
+        asan_unpoison_memory_region(&page->freelist, sizeof(RVALUE*), false);
+        if (page->freelist) {
+            RVALUE *p = page->freelist;
+            asan_unpoison_object((VALUE)p, false);
+            while (p->as.free.next) {
+                RVALUE *prev = p;
+                p = p->as.free.next;
+                asan_poison_object((VALUE)prev);
+                asan_unpoison_object((VALUE)p, false);
+            }
+            p->as.free.next = freelist;
+            asan_poison_object((VALUE)p);
+        }
+        else {
+            page->freelist = freelist;
+        }
+        asan_poison_memory_region(&page->freelist, sizeof(RVALUE*));
+    }
+
+    newobj_cache->using_page = NULL;
+    newobj_cache->freelist = NULL;
+}
+
+void
 rb_gc_force_recycle(VALUE obj)
 {
     rb_objspace_t *objspace = &rb_objspace;
diff --git a/internal/gc.h b/internal/gc.h
index 86a2512c85..ba2882af13 100644
--- a/internal/gc.h
+++ b/internal/gc.h
@@ -73,6 +73,11 @@ struct rb_objspace; /* in vm_core.h */
 
 #define RVARGC_PAYLOAD_INIT(obj, size) (void *)rb_rvargc_payload_init((VALUE)obj, (size_t)size)
 
+typedef struct ractor_newobj_cache {
+    struct RVALUE *freelist;
+    struct heap_page *using_page;
+} rb_ractor_newobj_cache_t;
+
 /* gc.c */
 extern VALUE *ruby_initial_gc_stress_ptr;
 extern int ruby_disable_gc;
@@ -115,6 +120,7 @@ void *ruby_sized_xrealloc(void *ptr, size_t new_size, size_t old_size) RUBY_ATTR
 void *ruby_sized_xrealloc2(void *ptr, size_t new_count, size_t element_size, size_t old_count) RUBY_ATTR_RETURNS_NONNULL RUBY_ATTR_ALLOC_SIZE((2, 3));
 void ruby_sized_xfree(void *x, size_t size);
 int rb_slot_size(void);
+void rb_gc_ractor_newobj_cache_clear(rb_ractor_newobj_cache_t *newobj_cache);
 RUBY_SYMBOL_EXPORT_END
 
 MJIT_SYMBOL_EXPORT_BEGIN
diff --git a/ractor.c b/ractor.c
index b5835a8ca6..7996d1c275 100644
--- a/ractor.c
+++ b/ractor.c
@@ -1486,6 +1486,9 @@ vm_remove_ractor(rb_vm_t *vm, rb_ractor_t *cr)
         }
         vm->ractor.cnt--;
 
+        /* Clear the cached freelist to prevent a memory leak. */
+        rb_gc_ractor_newobj_cache_clear(&cr->newobj_cache);
+
         ractor_status_set(cr, ractor_terminated);
     }
     RB_VM_UNLOCK();
diff --git a/ractor_core.h b/ractor_core.h
index 63279ebb98..879d8683fe 100644
--- a/ractor_core.h
+++ b/ractor_core.h
@@ -139,10 +139,7 @@ struct rb_ractor_struct {
     VALUE verbose;
     VALUE debug;
 
-    struct {
-        struct RVALUE *freelist;
-        struct heap_page *using_page;
-    } newobj_cache;
+    rb_ractor_newobj_cache_t newobj_cache;
 
     // gc.c rb_objspace_reachable_objects_from
     struct gc_mark_func_data_struct {