From: Austin Clements <austin@google.com>
Date: Fri, 11 Dec 2015 22:50:02 +0000 (-0500)
Subject: runtime: check for spanBytesAlloc underflow
X-Git-Tag: go1.6beta1~83
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c1cbe5b577b1bfdc34be18f391ab82904b6530f2;p=gostls13.git

runtime: check for spanBytesAlloc underflow

Change-Id: I5e6739ff0c6c561195ed9891fb90f933b81e7750
Reviewed-on: https://go-review.googlesource.com/17746
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
---

diff --git a/src/runtime/mgcsweep.go b/src/runtime/mgcsweep.go
index 22f51dbc1a..2cf6def338 100644
--- a/src/runtime/mgcsweep.go
+++ b/src/runtime/mgcsweep.go
@@ -393,7 +393,9 @@ func reimburseSweepCredit(unusableBytes uintptr) {
 		// Nobody cares about the credit. Avoid the atomic.
 		return
 	}
-	atomic.Xadd64(&mheap_.spanBytesAlloc, -int64(unusableBytes))
+	if int64(atomic.Xadd64(&mheap_.spanBytesAlloc, -int64(unusableBytes))) < 0 {
+		throw("spanBytesAlloc underflow")
+	}
 }
 
 func dumpFreeList(s *mspan) {