From 71a76476627fb0752d1b816406da4e5a6511c2c9 Mon Sep 17 00:00:00 2001

From: Austin Clements <[email protected]>

Date: Thu, 15 Oct 2015 13:25:19 -0400

Subject: [PATCH 27/63] [release-branch.go1.5] runtime: fix recursive GC assist

 better

Commit c257dfb attempted to fix recursive allocation in gcAssistAlloc;

however, it only reduced it: setting gp.gcalloc to 0 isn't sufficient

to disable assists at the beginning of the GC cycle when gp.gcscanwork

is also small or zero.

Fix this recursion more completely by setting gcalloc to a sentinel

value that directly disables assists.

Fixes #12894 (again).

Change-Id: I9599566222d8f540d0b39806846bfc702e6666e5

Reviewed-on: https://go-review.googlesource.com/15891

Run-TryBot: Austin Clements <[email protected]>

TryBot-Result: Gobot Gobot <[email protected]>

Reviewed-by: Russ Cox <[email protected]>

---

 src/runtime/mgcmark.go | 7 ++++++-

 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go

index e5dfa72..64cc1af 100644

--- a/src/runtime/mgcmark.go

+++ b/src/runtime/mgcmark.go

@@ -152,6 +152,11 @@ func gcAssistAlloc(size uintptr, allowAssist bool) {

 	}

 	// Record allocation.

+	if gp.gcalloc+size < gp.gcalloc {

+		// gcalloc would overflow, or it's set to a sentinel

+		// value to prevent recursive assist.

+		return

+	}

 	gp.gcalloc += size

 	if !allowAssist {

@@ -295,7 +300,7 @@ retry:

 		// timeSleep may allocate, so avoid recursive assist.

 		gcalloc := gp.gcalloc

-		gp.gcalloc = 0

+		gp.gcalloc = ^uintptr(0)

 		timeSleep(100 * 1000)

 		gp.gcalloc = gcalloc

 		goto retry

-- 

2.6.1