From eec8dd08362dc985a91bfead02107727b4643dcc Mon Sep 17 00:00:00 2001 From: Michael Anthony Knyszek Date: Wed, 2 Apr 2025 01:37:30 +0000 Subject: [PATCH] runtime: add scan trace for checkfinalizers>1 This change dumps a scan trace (each pointer marked and where it came from) for the partial GC cycle performed by checkfinalizers mode when checkfinalizers>1. This is useful for quickly understanding why certain values are reachable without having to pull out tools like viewcore. For #72949. Change-Id: Ic583f80e9558cdfe1c667d27a1d975008dd39a9c Reviewed-on: https://go-review.googlesource.com/c/go/+/662038 Reviewed-by: Michael Pratt Reviewed-by: Carlos Amedee Auto-Submit: Michael Knyszek LUCI-TryBot-Result: Go LUCI --- src/runtime/mcheckmark.go | 6 ++++++ src/runtime/mgcmark.go | 3 +++ 2 files changed, 9 insertions(+) diff --git a/src/runtime/mcheckmark.go b/src/runtime/mcheckmark.go index ebb19a0ceb..318f40f2eb 100644 --- a/src/runtime/mcheckmark.go +++ b/src/runtime/mcheckmark.go @@ -177,6 +177,9 @@ func checkFinalizersAndCleanups() { } // Run a checkmark GC using this cleanup and/or finalizer as a root. + if debug.checkfinalizers > 1 { + print("Scan trace for cleanup/finalizer on ", hex(p), ":\n") + } runCheckmark(func(gcw *gcWork) { switch sp.kind { case _KindSpecialFinalizer: @@ -185,6 +188,9 @@ func checkFinalizersAndCleanups() { gcScanCleanup((*specialCleanup)(unsafe.Pointer(sp)), gcw) } }) + if debug.checkfinalizers > 1 { + println() + } // Now check to see if the object the special is attached to was marked. // The roots above do not directly mark p, so if it is marked, then p diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go index 41a4b1ab5a..b5318e56f8 100644 --- a/src/runtime/mgcmark.go +++ b/src/runtime/mgcmark.go @@ -1665,6 +1665,9 @@ func greyobject(obj, base, off uintptr, span *mspan, gcw *gcWork, objIndex uintp // Already marked. return } + if debug.checkfinalizers > 1 { + print(" mark ", hex(obj), " found at *(", hex(base), "+", hex(off), ")\n") + } } else { if debug.gccheckmark > 0 && span.isFree(objIndex) { print("runtime: marking free object ", hex(obj), " found at *(", hex(base), "+", hex(off), ")\n") -- 2.51.0