code review 124670043: runtime: fix deadlock when gctrace

src/pkg/runtime/mheap.c

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Page heap.
 //
 // See malloc.h for overview.
 //
 // When a MSpan is in the heap free list, state == MSpanFree
 // and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
@@ skipping 601 matching lines @@
 ········
         h = &runtime·mheap;
         sumreleased = 0;
         for(i=0; i < nelem(h->free); i++)
                 sumreleased += scavengelist(&h->free[i], now, limit);
         sumreleased += scavengelist(&h->freelarge, now, limit);
 
         if(runtime·debug.gctrace > 0) {
                 if(sumreleased > 0)
                         runtime·printf("scvg%d: %D MB released\n", k, (uint64)sumreleased>>20);
+                // TODO(dvyukov): these stats are incorrect as we don't subtract stack usage from heap.
+                // But we can't call ReadMemStats on g0 holding locks.
                 runtime·printf("scvg%d: inuse: %D, idle: %D, sys: %D, released: %D, consumed: %D (MB)\n",
                         k, mstats.heap_inuse>>20, mstats.heap_idle>>20, mstats.heap_sys>>20,
                         mstats.heap_released>>20, (mstats.heap_sys - mstats.heap_released)>>20);
         }
 }
 
 static void
 scavenge_m(G *gp)
 {
         runtime·lock(&runtime·mheap.lock);
@@ skipping 301 matching lines @@
                 runtime·MProf_Free(sp->b, size, freed);
                 runtime·lock(&runtime·mheap.speciallock);
                 runtime·FixAlloc_Free(&runtime·mheap.specialprofilealloc, sp);
                 runtime·unlock(&runtime·mheap.speciallock);
                 return true;
         default:
                 runtime·throw("bad special kind");
                 return true;
         }
 }