runtime: fix memory allocator for GOMAXPROCS > 1

Bitmaps were not being updated safely.
Depends on 4188053.

Fixes #1504.
May fix issue 1479.

R=r, r2
CC=golang-dev
https://golang.org/cl/4184048

1 files changed, 7 insertions, 1 deletions

diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index 70b85d68d7..745e18ca0d 100644
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -146,6 +146,9 @@ runtime·free(void *v)
 		// Large object.
 		size = s->npages<<PageShift;
 		*(uintptr*)(s->start<<PageShift) = 1;	// mark as "needs to be zeroed"
+		// Must mark v freed before calling unmarkspan and MHeap_Free:
+		// they might coalesce v into other spans and change the bitmap further.
+		runtime·markfreed(v, size);
 		runtime·unmarkspan(v, 1<<PageShift);
 		runtime·MHeap_Free(&runtime·mheap, s, 1);
 	} else {
@@ -154,10 +157,13 @@ runtime·free(void *v)
 		size = runtime·class_to_size[sizeclass];
 		if(size > sizeof(uintptr))
 			((uintptr*)v)[1] = 1;	// mark as "needs to be zeroed"
+		// Must mark v freed before calling MCache_Free:
+		// it might coalesce v and other blocks into a bigger span
+		// and change the bitmap further.
+		runtime·markfreed(v, size);
 		mstats.by_size[sizeclass].nfree++;
 		runtime·MCache_Free(c, v, sizeclass, size);
 	}
-	runtime·markfreed(v, size);
 	mstats.alloc -= size;
 	if(prof)
 		runtime·MProf_Free(v, size);