hakmem/core/tiny_superslab_free.inc.h

// tiny_superslab_free.inc.h - SuperSlab Free Layer
// Purpose: Same-thread and cross-thread free handling
// Extracted from: hakmem_tiny_free.inc lines 1171-1475
// Box Theory: Box 6 (Free Fast Path) + Box 2 (Remote Queue) integration
//
// Public functions:
// - hak_tiny_free_superslab(): Main SuperSlab free entry point

#include <stdatomic.h>

// Phase 6.22-B: SuperSlab fast free path
static inline void hak_tiny_free_superslab(void* ptr, SuperSlab* ss) {
    // Route trace: count SuperSlab free entries (diagnostics only)
    extern _Atomic uint64_t g_free_ss_enter;
    atomic_fetch_add_explicit(&g_free_ss_enter, 1, memory_order_relaxed);
    ROUTE_MARK(16); // free_enter
    HAK_DBG_INC(g_superslab_free_count);  // Phase 7.6: Track SuperSlab frees

    // ✅ FIX: Convert USER → BASE at entry point (single conversion)
    // Phase E1-CORRECT: ALL classes (C0-C7) have 1-byte header
    // ptr = USER pointer (storage+1), base = BASE pointer (storage)
    void* base = (void*)((uint8_t*)ptr - 1);

    // Get slab index (supports 1MB/2MB SuperSlabs)
    // CRITICAL: Use BASE pointer for slab_index calculation!
    int slab_idx = slab_index_for(ss, base);
    size_t ss_size = (size_t)1ULL << ss->lg_size;
    uintptr_t ss_base = (uintptr_t)ss;
    if (__builtin_expect(slab_idx < 0, 0)) {
        uintptr_t aux = tiny_remote_pack_diag(0xBAD1u, ss_base, ss_size, (uintptr_t)ptr);
        tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, 0xFFu, ptr, aux);
        if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
        return;
    }
    TinySlabMeta* meta = &ss->slabs[slab_idx];
    uint8_t cls = meta->class_idx;
    
    // Debug: Log first C7 alloc/free for path verification
    if (cls == 7) {
        static _Atomic int c7_free_count = 0;
        int count = atomic_fetch_add_explicit(&c7_free_count, 1, memory_order_relaxed);
        if (count == 0) {
            #if !HAKMEM_BUILD_RELEASE && HAKMEM_DEBUG_VERBOSE
            fprintf(stderr, "[C7_FIRST_FREE] ptr=%p base=%p slab_idx=%d\n", ptr, base, slab_idx);
            #endif
        }
    }
    if (__builtin_expect(tiny_remote_watch_is(ptr), 0)) {
        tiny_remote_watch_note("free_enter", ss, slab_idx, ptr, 0xA240u, tiny_self_u32(), 0);
        extern __thread TinyTLSSlab g_tls_slabs[];
        tiny_alloc_dump_tls_state(cls, "watch_free_enter", &g_tls_slabs[cls]);
#if !HAKMEM_BUILD_RELEASE
        extern __thread TinyTLSMag g_tls_mags[];
        TinyTLSMag* watch_mag = &g_tls_mags[cls];
        fprintf(stderr,
                "[REMOTE_WATCH_MAG] cls=%u mag_top=%d cap=%d\n",
                cls,
                watch_mag->top,
                watch_mag->cap);
#endif
    }
    // BUGFIX (Phase 12): Validate class_idx before using as array index
    if (__builtin_expect(cls >= TINY_NUM_CLASSES, 0)) {
        tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, 0xF1, ptr, (uintptr_t)cls);
        if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
        return;
    }
    // ChatGPT Pro Optimization: Move safety checks to debug mode only
    // In release builds, these checks are completely eliminated by the compiler
    // Expected impact: -10~-15% CPU (eliminates O(n) duplicate scan)
#if !HAKMEM_BUILD_RELEASE
    if (__builtin_expect(g_tiny_safe_free, 0)) {
        size_t blk = g_tiny_class_sizes[cls];
        uint8_t* base = tiny_slab_base_for(ss, slab_idx);
        uintptr_t delta = (uintptr_t)ptr - (uintptr_t)base;
        int cap_ok = (meta->capacity > 0) ? 1 : 0;
        int align_ok = (delta % blk) == 0;
        int range_ok = cap_ok && (delta / blk) < meta->capacity;
        if (!align_ok || !range_ok) {
            uint32_t code = 0xA100u;
            if (align_ok) code |= 0x2u;
            if (range_ok) code |= 0x1u;
            uintptr_t aux = tiny_remote_pack_diag(code, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
            return;
        }
        // Duplicate in freelist (best-effort scan up to 64)
        // NOTE: This O(n) scan is VERY expensive (can scan 64 pointers per free!)
        void* scan = meta->freelist; int scanned = 0; int dup = 0;
        while (scan && scanned < 64) { if (scan == base) { dup = 1; break; } scan = tiny_next_read(cls, scan); scanned++; }
        if (dup) {
            uintptr_t aux = tiny_remote_pack_diag(0xDFu, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
            return;
        }
    }
#endif // !HAKMEM_BUILD_RELEASE

    // Phase E1-CORRECT: C7 now has headers like other classes
    // Validation must check base pointer (ptr-1) alignment, not user pointer
    if (__builtin_expect(cls == 7, 0)) {
        size_t blk = g_tiny_class_sizes[cls];
        uint8_t* slab_base = tiny_slab_base_for(ss, slab_idx);
        uintptr_t delta = (uintptr_t)base - (uintptr_t)slab_base;
        int cap_ok = (meta->capacity > 0) ? 1 : 0;
        int align_ok = (delta % blk) == 0;
        int range_ok = cap_ok && (delta / blk) < meta->capacity;
        if (!align_ok || !range_ok) {
            uintptr_t aux = tiny_remote_pack_diag(0xA107u, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
#if !HAKMEM_BUILD_RELEASE
            // Debug build: Print diagnostic info before failing
            fprintf(stderr, "[C7_ALIGN_CHECK_FAIL] ptr=%p base=%p slab_base=%p\n", ptr, base, (void*)slab_base);
            fprintf(stderr, "[C7_ALIGN_CHECK_FAIL] delta=%zu blk=%zu delta%%blk=%zu\n",
                    (size_t)delta, blk, (size_t)(delta % blk));
            fprintf(stderr, "[C7_ALIGN_CHECK_FAIL] align_ok=%d range_ok=%d cap=%u capacity=%u\n",
                    align_ok, range_ok, (unsigned)(delta / blk), (unsigned)meta->capacity);
#endif
            // BUGFIX: Guard with g_tiny_safe_free_strict like other validation checks
            // Fail-fast in class7 to avoid silent SLL/freelist corruption (only if strict mode enabled)
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); }
            return;
        }
    }

    // Header vs meta class mismatch detector（env: HAKMEM_TINY_SLL_DIAG、初回数件のみ）
    do {
        static int g_hdr_diag_en = -1;
        if (__builtin_expect(g_hdr_diag_en == -1, 0)) {
            const char* e = getenv("HAKMEM_TINY_SLL_DIAG");
            g_hdr_diag_en = (e && *e && *e != '0') ? 1 : 0;
        }
        if (__builtin_expect(g_hdr_diag_en, 0)) {
            uint8_t hdr = *(uint8_t*)base;
            uint8_t expect = (uint8_t)(HEADER_MAGIC | (cls & HEADER_CLASS_MASK));
            if (__builtin_expect(hdr != expect, 0)) {
                static _Atomic uint32_t g_hdr_mismatch_log = 0;
                uint32_t n = atomic_fetch_add_explicit(&g_hdr_mismatch_log, 1, memory_order_relaxed);
                if (n < 8) {
                    fprintf(stderr,
                            "[TLS_HDR_MISMATCH] cls=%u slab_idx=%d hdr=0x%02x expect=0x%02x ptr=%p\n",
                            (unsigned)cls, slab_idx, hdr, expect, ptr);
                }
            }
        }
    } while (0);

    // Phase 6.23: Same-thread check (Phase 12: owner_tid_low)
    uint32_t my_tid = tiny_self_u32();
    uint8_t my_tid_low = (uint8_t)my_tid;
    const int debug_guard = g_debug_remote_guard;
    static __thread int g_debug_free_count = 0;
    // If owner is not set yet, claim ownership (low 8 bits) to avoid spurious remote path in 1T
    if (!g_tiny_force_remote && meta->owner_tid_low == 0) {
        meta->owner_tid_low = my_tid_low;
    }
    if (!g_tiny_force_remote && meta->owner_tid_low != 0 && meta->owner_tid_low == my_tid_low) {
        ROUTE_MARK(17); // free_same_thread
        // Fast path: Direct freelist push (same-thread)
        if (0 && debug_guard && g_debug_free_count < 1) {
            fprintf(stderr, "[FREE_SS] SAME-THREAD: owner=%u my=%u\n",
                    meta->owner_tid_low, my_tid);
            g_debug_free_count++;
        }
        // Header/meta class cross-check (triage)
#if HAKMEM_TINY_HEADER_CLASSIDX
        do {
            uint8_t hdr_cls = tiny_region_id_read_header(ptr);
            uint8_t meta_cls = meta->class_idx;
            if (__builtin_expect(hdr_cls >= 0 && hdr_cls != meta_cls, 0)) {
                static _Atomic uint32_t g_hdr_meta_mismatch = 0;
                uint32_t n = atomic_fetch_add_explicit(&g_hdr_meta_mismatch, 1, memory_order_relaxed);
                if (n < 16) {
                    fprintf(stderr, "[SLAB_HDR_META_MISMATCH] slab_push cls_meta=%u hdr_cls=%u ptr=%p slab_idx=%d ss=%p freelist=%p used=%u\n",
                            (unsigned)meta_cls, (unsigned)hdr_cls, ptr, slab_idx, (void*)ss, meta->freelist, (unsigned)meta->used);
                }
            }
        } while (0);
#endif
        if (__builtin_expect(meta->used == 0, 0)) {
            uintptr_t aux = tiny_remote_pack_diag(0x00u, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
            return;
        }
        tiny_remote_track_expect_alloc(ss, slab_idx, ptr, "local_free_enter", my_tid);
        if (!tiny_remote_guard_allow_local_push(ss, slab_idx, meta, ptr, "local_free", my_tid)) {
            #include "box/free_remote_box.h"
            int transitioned = tiny_free_remote_box(ss, slab_idx, meta, base, my_tid);
            if (transitioned) {
                extern unsigned long long g_remote_free_transitions[];
                g_remote_free_transitions[cls]++;
                // Free-side route: remote transition observed
                do {
                    static int g_route_free = -1; if (__builtin_expect(g_route_free == -1, 0)) {
                        const char* e = getenv("HAKMEM_TINY_ROUTE_FREE");
                        g_route_free = (e && *e && *e != '0') ? 1 : 0; }
                    if (g_route_free) route_free_commit((int)cls, (1ull<<18), 0xE2);
                } while (0);
            }
            return;
        }
        // Optional: MidTC (TLS tcache for 128..1024B) — allow bypass via env HAKMEM_TINY_FREE_TO_SS=1
        do {
            static int g_free_to_ss = -1;
            if (__builtin_expect(g_free_to_ss == -1, 0)) {
                const char* e = getenv("HAKMEM_TINY_FREE_TO_SS");
                g_free_to_ss = (e && *e && *e != '0') ? 1 : 0; // default OFF
            }
            if (!g_free_to_ss) {
                int mid_cls = (int)cls;
                if (midtc_enabled() && mid_cls >= 4) {
                    if (midtc_push(mid_cls, base)) {
                        // Treat as returned to TLS cache (not SS freelist)
                        meta->used--;
                        ss_active_dec_one(ss);
                        return;
                    }
                }
            }
        } while (0);

        #include "box/free_local_box.h"
        // DEBUG LOGGING - Track freelist operations
        static __thread int dbg = -1;
        if (__builtin_expect(dbg == -1, 0)) {
            const char* e = getenv("HAKMEM_SS_FREE_DEBUG");
            dbg = (e && *e && *e != '0') ? 1 : 0;
        }
        static __thread int free_count = 0;
        if (dbg == 1 && (free_count++ % 1000) == 0) {
            fprintf(stderr, "[FREE_LOCAL] cls=%u slab=%d meta->used=%u (before dec)\n",
                    cls, slab_idx, meta->used);
        }

        // Perform freelist push (+first-free publish if applicable)
        void* prev_before = meta->freelist;
        tiny_free_local_box(ss, slab_idx, meta, base, my_tid);
        if (prev_before == NULL) {
            ROUTE_MARK(19); // first_free_transition
            extern unsigned long long g_first_free_transitions[];
            g_first_free_transitions[cls]++;
            ROUTE_MARK(20); // mailbox_publish
            // Free-side route commit (one-shot)
            do {
                static int g_route_free = -1; if (__builtin_expect(g_route_free == -1, 0)) {
                    const char* e = getenv("HAKMEM_TINY_ROUTE_FREE");
                    g_route_free = (e && *e && *e != '0') ? 1 : 0; }
                if (g_route_free) route_free_commit(cls, (1ull<<19) | (1ull<<20), 0xE1);
            } while (0);
        }

        if (__builtin_expect(debug_guard, 0)) {
                    fprintf(stderr, "[REMOTE_LOCAL] cls=%u slab=%d owner=%u my=%u ptr=%p prev=%p used=%u\n",
                    cls, slab_idx, meta->owner_tid_low, my_tid, ptr, prev_before, meta->used);
        }

        // 空検出は別途（ホットパス除外）
        // Phase 12: slab empty → shared pool に返却
        if (meta->used == 0) {
            // DEBUG LOGGING
            static __thread int dbg = -1;
            if (__builtin_expect(dbg == -1, 0)) {
                const char* e = getenv("HAKMEM_SS_FREE_DEBUG");
                dbg = (e && *e && *e != '0') ? 1 : 0;
            }
            if (dbg == 1) {
                fprintf(stderr, "[FREE_PATH] meta->used=0 detected: cls=%u ss=%p slab_idx=%d\n",
                        cls, (void*)ss, slab_idx);
            }
            extern void shared_pool_release_slab(SuperSlab* ss, int slab_idx);
            shared_pool_release_slab(ss, slab_idx);
        }
    } else {
        ROUTE_MARK(18); // free_remote_transition
        if (__builtin_expect(meta->owner_tid_low == my_tid_low && meta->owner_tid_low == 0, 0)) {
            uintptr_t aux = tiny_remote_pack_diag(0xA300u, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (debug_guard) {
                fprintf(stderr, "[REMOTE_OWNER_ZERO] cls=%u slab=%d ptr=%p my=%u used=%u\n",
                        cls, slab_idx, ptr, my_tid, (unsigned)meta->used);
            }
        }
        tiny_remote_track_expect_alloc(ss, slab_idx, ptr, "remote_free_enter", my_tid);
        // Slow path: Remote free (cross-thread)
        if (0 && debug_guard && g_debug_free_count < 5) {
            fprintf(stderr, "[FREE_SS] CROSS-THREAD: owner=%u my=%u slab_idx=%d\n",
                    meta->owner_tid_low, my_tid, slab_idx);
            g_debug_free_count++;
        }
        if (__builtin_expect(g_tiny_safe_free, 0)) {
            // Best-effort duplicate scan in remote stack (up to 64 nodes)
            uintptr_t head = atomic_load_explicit(&ss->remote_heads[slab_idx], memory_order_acquire);
            uintptr_t base = ss_base;
            int scanned = 0; int dup = 0;
            uintptr_t cur = head;
            while (cur && scanned < 64) {
                if ((cur < base) || (cur >= base + ss_size)) {
                    uintptr_t aux = tiny_remote_pack_diag(0xA200u, base, ss_size, cur);
                    tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, (void*)cur, aux);
                    if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
                    break;
                }
                if ((void*)cur == ptr) { dup = 1; break; }
                if (__builtin_expect(g_remote_side_enable, 0)) {
                    if (!tiny_remote_sentinel_ok((void*)cur)) {
                        uintptr_t aux = tiny_remote_pack_diag(0xA202u, base, ss_size, cur);
                        tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, (void*)cur, aux);
                        tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, (void*)cur, aux);
                        uintptr_t observed = atomic_load_explicit((_Atomic uintptr_t*)(void*)cur, memory_order_relaxed);
                        tiny_remote_report_corruption("scan", (void*)cur, observed);
                        if (__builtin_expect(g_debug_remote_guard, 0)) {
                            fprintf(stderr,
                                    "[REMOTE_SENTINEL] cls=%u slab=%d cur=%p head=%p ptr=%p scanned=%d observed=0x%016" PRIxPTR " owner=%u used=%u freelist=%p remote_head=%p\n",
                                    cls,
                                    slab_idx,
                                    (void*)cur,
                                    (void*)head,
                                    ptr,
                                    scanned,
                                    observed,
                                    meta->owner_tid_low,
                                    (unsigned)meta->used,
                                    meta->freelist,
                                    (void*)atomic_load_explicit(&ss->remote_heads[slab_idx], memory_order_relaxed));
                        }
                        if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
                        break;
                    }
                    cur = tiny_remote_side_get(ss, slab_idx, (void*)cur);
                } else {
                    if ((cur & (uintptr_t)(sizeof(void*) - 1)) != 0) {
                        uintptr_t aux = tiny_remote_pack_diag(0xA201u, base, ss_size, cur);
                        tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, (void*)cur, aux);
                        if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
                        break;
                    }
                    cur = (uintptr_t)tiny_next_read(cls, (void*)cur);
                }
                scanned++;
            }
            if (dup) {
            uintptr_t aux = tiny_remote_pack_diag(0xD1u, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
            return;
        }
        }
        if (__builtin_expect(meta->used == 0, 0)) {
            uintptr_t aux = tiny_remote_pack_diag(0x01u, ss_base, ss_size, (uintptr_t)ptr);
            tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
            if (g_tiny_safe_free_strict) { raise(SIGUSR2); return; }
            return;
        }
        static int g_ss_adopt_en2 = -1; // env cached
        if (g_ss_adopt_en2 == -1) {
            char* e = getenv("HAKMEM_TINY_SS_ADOPT");
            // 既定: Remote Queueを使う（1）。env指定時のみ上書き。
            g_ss_adopt_en2 = (e == NULL) ? 1 : ((*e != '0') ? 1 : 0);
            if (__builtin_expect(debug_guard, 0)) {
                fprintf(stderr, "[FREE_SS] g_ss_adopt_en2=%d (env='%s')\n", g_ss_adopt_en2, e ? e : "(null)");
            }
        }
        // A/B gate: disable remote MPSC (use legacy freelist push)
        do {
            static int g_disable_remote = -1;
            if (__builtin_expect(g_disable_remote == -1, 0)) {
                const char* e = getenv("HAKMEM_TINY_DISABLE_REMOTE");
                g_disable_remote = (e && *e && *e != '0') ? 1 : 0;
            }
            if (__builtin_expect(g_disable_remote, 0)) {
                g_ss_adopt_en2 = 0;
            }
        } while (0);
        if (g_ss_adopt_en2) {
            // Use remote queue
            uintptr_t head_word = __atomic_load_n((uintptr_t*)base, __ATOMIC_RELAXED);
            if (debug_guard) fprintf(stderr, "[REMOTE_PUSH_CALL] cls=%u slab=%d owner=%u my=%u ptr=%p used=%u remote_count=%u head=%p word=0x%016" PRIxPTR "\n",
                    cls,
                    slab_idx,
                    meta->owner_tid_low,
                    my_tid,
                    ptr,
                    (unsigned)meta->used,
                    atomic_load_explicit(&ss->remote_counts[slab_idx], memory_order_relaxed),
                    (void*)atomic_load_explicit(&ss->remote_heads[slab_idx], memory_order_relaxed),
                    head_word);
            int dup_remote = tiny_remote_queue_contains_guard(ss, slab_idx, base);
            if (!dup_remote && __builtin_expect(g_remote_side_enable, 0)) {
                dup_remote = (head_word == TINY_REMOTE_SENTINEL) || tiny_remote_side_contains(ss, slab_idx, base);
            }
            if (__builtin_expect(head_word == TINY_REMOTE_SENTINEL && !dup_remote && g_debug_remote_guard, 0)) {
                tiny_remote_watch_note("dup_scan_miss", ss, slab_idx, ptr, 0xA215u, my_tid, 0);
            }
            if (dup_remote) {
                uintptr_t aux = tiny_remote_pack_diag(0xA214u, ss_base, ss_size, (uintptr_t)ptr);
                tiny_remote_watch_mark(ptr, "dup_prevent", my_tid);
                tiny_remote_watch_note("dup_prevent", ss, slab_idx, ptr, 0xA214u, my_tid, 0);
                tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
                tiny_failfast_abort_ptr("double_free_remote", ss, slab_idx, ptr, "remote_side_contains");
            }
            if (__builtin_expect(g_remote_side_enable && (head_word & 0xFFFFu) == 0x6261u, 0)) {
                // TLS guard scribble detected on the node's first word → same-pointer double free across routes
                uintptr_t aux = tiny_remote_pack_diag(0xA213u, ss_base, ss_size, (uintptr_t)ptr);
                tiny_debug_ring_record(TINY_RING_EVENT_REMOTE_INVALID, (uint16_t)cls, ptr, aux);
                tiny_remote_watch_mark(ptr, "pre_push", my_tid);
                tiny_remote_watch_note("pre_push", ss, slab_idx, ptr, 0xA231u, my_tid, 0);
                tiny_remote_report_corruption("pre_push", ptr, head_word);
                tiny_failfast_abort_ptr("double_free_scribble", ss, slab_idx, ptr, "scribble_6261");
            }
            if (__builtin_expect(tiny_remote_watch_is(ptr), 0)) {
                tiny_remote_watch_note("free_remote", ss, slab_idx, ptr, 0xA232u, my_tid, 0);
            }
            int was_empty = ss_remote_push(ss, slab_idx, base);  // ss_active_dec_one() called inside
            meta->used--;
            // ss_active_dec_one(ss);  // REMOVED: Already called inside ss_remote_push()
            if (was_empty) {
                extern unsigned long long g_remote_free_transitions[];
                g_remote_free_transitions[cls]++;
                g_remote_free_transitions[cls]++;
                ss_partial_publish((int)cls, ss);
            }
        } else {
            // Fallback: direct freelist push (legacy)
            if (debug_guard) fprintf(stderr, "[FREE_SS] Using LEGACY freelist push (not remote queue)\n");
            void* prev = meta->freelist;
            tiny_next_write(cls, base, prev);
            meta->freelist = base;
            tiny_failfast_log("free_local_legacy", cls, ss, meta, ptr, prev);
            do {
                static int g_mask_en = -1;
                if (__builtin_expect(g_mask_en == -1, 0)) {
                    const char* e = getenv("HAKMEM_TINY_FREELIST_MASK");
                    g_mask_en = (e && *e && *e != '0') ? 1 : 0;
                }
                if (__builtin_expect(g_mask_en, 0) && prev == NULL) {
                    uint32_t bit = (1u << slab_idx);
                    atomic_fetch_or_explicit(&ss->freelist_mask, bit, memory_order_release);
                }
            } while (0);
            meta->used--;
            ss_active_dec_one(ss);
            if (prev == NULL) {
                ss_partial_publish((int)cls, ss);
            }
        }

        // 空検出は別途（ホットパス除外）
        // Phase 12: slab empty → shared pool に返却
        if (meta->used == 0) {
            // DEBUG LOGGING
            static __thread int dbg = -1;
            if (__builtin_expect(dbg == -1, 0)) {
                const char* e = getenv("HAKMEM_SS_FREE_DEBUG");
                dbg = (e && *e && *e != '0') ? 1 : 0;
            }
            if (dbg == 1) {
                fprintf(stderr, "[FREE_PATH] meta->used=0 detected: cls=%u ss=%p slab_idx=%d\n",
                        cls, (void*)ss, slab_idx);
            }
            extern void shared_pool_release_slab(SuperSlab* ss, int slab_idx);
            shared_pool_release_slab(ss, slab_idx);
        }
    }
}