youknowone · youknowone · Aug 26, 2026 · Aug 26, 2026 · Aug 26, 2026 · Aug 26, 2026
diff --git a/majit/majit-gc/src/collector.rs b/majit/majit-gc/src/collector.rs
@@ -7135,15 +7135,35 @@ impl MiniMarkGC {
         self.oldgen_nonmoving_active = true;
         self.oldgen_nonmoving_young_marks.clear();
 
-        if self.gc_state == GcState::Scanning {
-            self.start_incremental_cycle();
-        }
+        // `do_collect_full` / incminimark.py `gc_step_until` first finishes
+        // an in-progress major, then starts a fresh cycle whose root snapshot
+        // is taken at the explicit collection boundary.  The non-moving twin
+        // owes the same ordering: merely finishing an older cycle can retain
+        // an object which became unreachable after that cycle began.
+        if self.gc_state != GcState::Scanning {
+            self.gc_step_until_scanning();
+            self.clear_oldgen_nonmoving_young_marks();
+        }
+        self.start_incremental_cycle();
         // Keep this oldgen-only entry stop-the-world: it may enter while
         // MARKING or SWEEPING, but always returns after the complete cycle.
         self.gc_step_until_scanning();
 
         // Strictly-last: clear VISITED on every young object greyed this cycle
         // (the oldgen sweep already cleared it on old-gen survivors).
+        self.clear_oldgen_nonmoving_young_marks();
+        self.oldgen_nonmoving_active = false;
+
+        // This entry has no upstream counterpart, but it is a public collection
+        // entry point and it can queue mirrors, so it owes the same schedule.
+        self.rrc_invoke_callback();
+    }
+
+    /// Clear the nursery VISITED bits accumulated by one non-moving major.
+    /// A fresh explicit cycle must begin with those bits clear or its marker
+    /// will mistake the preceding cycle's young survivors for already-traced
+    /// objects and skip their old-generation children.
+    fn clear_oldgen_nonmoving_young_marks(&mut self) {
         let marks = std::mem::take(&mut self.oldgen_nonmoving_young_marks);
         for addr in marks {
             // Nothing moved and nothing young was freed, so each addr is still
@@ -7154,11 +7174,6 @@ impl MiniMarkGC {
                 unsafe { (*hdr).clear_flag(flags::VISITED) };
             }
         }
-        self.oldgen_nonmoving_active = false;
-
-        // This entry has no upstream counterpart, but it is a public collection
-        // entry point and it can queue mirrors, so it owes the same schedule.
-        self.rrc_invoke_callback();
     }
 
     fn gc_step_until_scanning(&mut self) {
@@ -13811,6 +13826,32 @@ cache size\t: 8192 kB\n";
         gc.roots.clear();
     }
 
+    /// An explicit non-moving collection must use roots observed at the call,
+    /// not merely finish an incremental cycle whose root snapshot predates a
+    /// release.  This is the non-moving counterpart of `do_collect_full`'s
+    /// initial `gc_step_until_scanning_with_minors` followed by a fresh cycle.
+    #[test]
+    fn nonmoving_major_starts_fresh_after_finishing_an_in_progress_cycle() {
+        let mut gc = test_gc(4096);
+        let tid = gc.register_type(TypeInfo::simple(16));
+        let object = gc.alloc_in_oldgen_clear(tid, GcHeader::SIZE + 16);
+        let mut root = object;
+        unsafe { gc.roots.add(&mut root) };
+
+        // Seed the in-progress cycle while `object` is live, then release it.
+        gc.major_collection_step();
+        assert_ne!(gc.gc_state, GcState::Scanning);
+        gc.roots.clear();
+
+        gc.do_collect_oldgen_nonmoving();
+
+        assert_eq!(
+            gc.oldgen.object_count(),
+            0,
+            "the explicit collection's fresh root snapshot must sweep object"
+        );
+    }
+
     /// A non-moving major must run `invalidate_old_weakrefs` (reads the
     /// target's VISITED) BEFORE the nursery-VISITED clear, so an old weakref
     /// whose target is a live nursery object is kept, not spuriously nulled.

diff --git a/majit/majit-metainterp/tests/jit_interp_label_entry_deopt_resume.rs b/majit/majit-metainterp/tests/jit_interp_label_entry_deopt_resume.rs
@@ -42,6 +42,11 @@ fn count_program(n: i64) -> Vec<i64> {
 }
 
 static COMPILES: AtomicU32 = AtomicU32::new(0);
+// Both tests install the same capture-free compile callback, hence share the
+// process-global counter.  Rust runs sibling tests concurrently; keep each
+// reset/run/read interval indivisible just as
+// `jit_interp_halt_arm_post_loop_expression::run` does for its probe.
+static PROBE_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());
 
 struct VmState {
     regs: Vec<i64>,
@@ -151,6 +156,7 @@ fn clean_interp(program: &Bytecode) -> i64 {
 
 #[test]
 fn a_label_entered_deopt_resumes_at_the_green_pc() {
+    let _guard = PROBE_LOCK.lock().unwrap_or_else(|e| e.into_inner());
     for n in [1_000i64, 1_001] {
         let program = count_program(n);
         COMPILES.store(0, Ordering::Relaxed);
@@ -179,6 +185,7 @@ fn a_label_entered_deopt_resumes_at_the_green_pc() {
 /// attributed to the compiled tier rather than to the bytecode or the fixture.
 #[test]
 fn the_same_machine_without_tracing_answers_n() {
+    let _guard = PROBE_LOCK.lock().unwrap_or_else(|e| e.into_inner());
     for n in [1_000i64, 1_001] {
         let program = count_program(n);
         COMPILES.store(0, Ordering::Relaxed);

diff --git a/pyre/bench/synth/bound_method_builtin_fold.cranelift.jitstats b/pyre/bench/synth/bound_method_builtin_fold.cranelift.jitstats
@@ -4,11 +4,14 @@ descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=468
+guard_failures=687
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=8

diff --git a/pyre/bench/synth/bound_method_builtin_fold.dynasm.jitstats b/pyre/bench/synth/bound_method_builtin_fold.dynasm.jitstats
@@ -4,11 +4,14 @@ descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=468
+guard_failures=687
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=8

diff --git a/pyre/bench/synth/bound_method_builtin_fold.wasm.jitstats b/pyre/bench/synth/bound_method_builtin_fold.wasm.jitstats
@@ -4,11 +4,14 @@ descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=468
+guard_failures=687
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=8

diff --git a/pyre/bench/synth/comprehension_object_append_hot.cranelift.jitstats b/pyre/bench/synth/comprehension_object_append_hot.cranelift.jitstats
@@ -1,14 +1,17 @@
-bridges_compiled=14
+bridges_compiled=10
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=2810
+guard_failures=2014
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/comprehension_object_append_hot.dynasm.jitstats b/pyre/bench/synth/comprehension_object_append_hot.dynasm.jitstats
@@ -1,14 +1,17 @@
-bridges_compiled=14
+bridges_compiled=10
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=2810
+guard_failures=2014
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/comprehension_object_append_hot.wasm.jitstats b/pyre/bench/synth/comprehension_object_append_hot.wasm.jitstats
@@ -1,14 +1,17 @@
-bridges_compiled=14
+bridges_compiled=10
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=2810
+guard_failures=2014
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/exception_catching_frame_tb_node.cranelift.jitstats b/pyre/bench/synth/exception_catching_frame_tb_node.cranelift.jitstats
@@ -1,14 +1,18 @@
-bridges_compiled=3
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=601
+guard_failures=401
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=3
+retraces_compiled=0
diff --git a/pyre/bench/synth/exception_catching_frame_tb_node.dynasm.jitstats b/pyre/bench/synth/exception_catching_frame_tb_node.dynasm.jitstats
@@ -1,14 +1,18 @@
-bridges_compiled=3
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=601
+guard_failures=401
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=3
+retraces_compiled=0
diff --git a/pyre/bench/synth/exception_catching_frame_tb_node.wasm.jitstats b/pyre/bench/synth/exception_catching_frame_tb_node.wasm.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=3
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=601
+guard_failures=401
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=3

diff --git a/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.cranelift.jitstats b/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.cranelift.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=5
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=807
+guard_failures=1007
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=11

diff --git a/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.dynasm.jitstats b/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.dynasm.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=5
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=807
+guard_failures=1007
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=11

diff --git a/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.wasm.jitstats b/pyre/bench/synth/exception_escape_hot_callee_tb_node_once.wasm.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=5
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=807
+guard_failures=1007
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=11

diff --git a/pyre/bench/synth/exception_inline_callee_tb_frames.cranelift.jitstats b/pyre/bench/synth/exception_inline_callee_tb_frames.cranelift.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=604
+guard_failures=403
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/exception_inline_callee_tb_frames.dynasm.jitstats b/pyre/bench/synth/exception_inline_callee_tb_frames.dynasm.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=604
+guard_failures=403
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/exception_inline_callee_tb_frames.wasm.jitstats b/pyre/bench/synth/exception_inline_callee_tb_frames.wasm.jitstats
@@ -1,4 +1,4 @@
-bridges_compiled=4
+bridges_compiled=2
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
@@ -11,7 +11,7 @@ fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=604
+guard_failures=403
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=6

diff --git a/pyre/bench/synth/exception_reentry_guard_finally_residual.cranelift.jitstats b/pyre/bench/synth/exception_reentry_guard_finally_residual.cranelift.jitstats
@@ -1,14 +1,18 @@
-bridges_compiled=12
+bridges_compiled=11
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
 fbw_blackhole_adopted_multi_frame=0
 fbw_blackhole_adopted_single_frame=0
+fbw_escape_plain_fallback=0
+fbw_escape_plain_fallback_unclean=0
+fbw_midbody_latch_new_unjournaled=0
 fbw_rolled_back_with_effects=0
 fbw_store_journal_rollback_failed=0
 field_pos_attached_misplaced=0
 field_pos_spec_misplaced=0
-guard_failures=2461
+guard_failures=2261
 internal_compile_panics=0
 loops_aborted=0
 loops_compiled=3
+retraces_compiled=0