From c257dfb178f00449dd344204219aad56e3e90de6 Mon Sep 17 00:00:00 2001
From: Austin Clements <[email protected]>
Date: Fri, 9 Oct 2015 17:20:34 -0400
Subject: [PATCH 26/63] [release-branch.go1.5] runtime: fix recursive GC assist

If gcAssistAlloc is unable to steal or perform enough scan work, it
calls timeSleep, which allocates. If this allocation requires
obtaining a new span, it will in turn attempt to assist GC. Since
there's likely still no way to satisfy the assist, it will sleep
again, and so on, leading to potentially deep (not infinite, but also
not bounded) recursion.

Fix this by disallowing assists during the timeSleep.

This same problem was fixed on master by 65aa2da. That commit built on
several other changes and hence can't be directly cherry-picked. This
commit implements the same idea.

Fixes #12894.

Change-Id: I152977eb1d0a3005c42ff3985d58778f054a86d4
Reviewed-on: https://go-review.googlesource.com/15720
Reviewed-by: Rick Hudson <[email protected]>
---
 src/runtime/mgcmark.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 44f9512..e5dfa72 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -292,7 +292,12 @@ retry:
 		// more, so go around again after performing an
 		// interruptible sleep for 100 us (the same as the
 		// getfull barrier) to let other mutators run.
+
+		// timeSleep may allocate, so avoid recursive assist.
+		gcalloc := gp.gcalloc
+		gp.gcalloc = 0
 		timeSleep(100 * 1000)
+		gp.gcalloc = gcalloc
 		goto retry
 	}
 }
-- 
2.6.1