From f5c6875f3228951afa1fcf2ec01c614e0fb7e2dd Mon Sep 17 00:00:00 2001 From: Michael Anthony Knyszek Date: Thu, 23 Jul 2020 20:24:56 +0000 Subject: runtime: make next_gc atomically accessed next_gc is mostly updated only during a STW, but may occasionally be updated by calls to e.g. debug.SetGCPercent. In this case the update is supposed to be protected by the heap lock, but in reality it's accessed by gcController.revise which may be called without the heap lock held (despite its documentation, which will be updated in a later change). Change the synchronization policy on next_gc so that it's atomically accessed when the world is not stopped to aid in making revise safe for concurrent use. Change-Id: I79657a72f91563f3241aaeda66e8a7757d399529 Reviewed-on: https://go-review.googlesource.com/c/go/+/246962 Trust: Michael Knyszek Run-TryBot: Michael Knyszek TryBot-Result: Go Bot Reviewed-by: Michael Pratt --- src/runtime/trace.go | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'src/runtime/trace.go') diff --git a/src/runtime/trace.go b/src/runtime/trace.go index 169b650eb4..d3ecd148be 100644 --- a/src/runtime/trace.go +++ b/src/runtime/trace.go @@ -13,6 +13,7 @@ package runtime import ( + "runtime/internal/atomic" "runtime/internal/sys" "unsafe" ) @@ -1146,11 +1147,11 @@ func traceHeapAlloc() { } func traceNextGC() { - if memstats.next_gc == ^uint64(0) { + if nextGC := atomic.Load64(&memstats.next_gc); nextGC == ^uint64(0) { // Heap-based triggering is disabled. traceEvent(traceEvNextGC, -1, 0) } else { - traceEvent(traceEvNextGC, -1, memstats.next_gc) + traceEvent(traceEvNextGC, -1, nextGC) } } -- cgit v1.3-6-g1900