runtime: properly synchronize GC and finalizer goroutine

This is needed for preemptive scheduler, because the goroutine
can be preempted at surprising points.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/9376043

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 28cc4353efa3826e6edc5da883fb48581afeba74..1ea3a1482eb2ec6c0d6ed7878a753e72f742894a 100644 (file)
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -2030,18 +2030,6 @@ gc(struct gc_args *args)
        mstats.next_gc = mstats.heap_alloc+mstats.heap_alloc*gcpercent/100;
        m->gcing = 0;
 
-       if(finq != nil) {
-               m->locks++;     // disable gc during the mallocs in newproc
-               // kick off or wake up goroutine to run queued finalizers
-               if(fing == nil)
-                       fing = runtime·newproc1(&runfinqv, nil, 0, 0, runtime·gc);
-               else if(fingwait) {
-                       fingwait = 0;
-                       runtime·ready(fing);
-               }
-               m->locks--;
-       }
-
        heap1 = mstats.heap_alloc;
        obj1 = mstats.nmalloc - mstats.nfree;
 
@@ -2089,9 +2077,19 @@ gc(struct gc_args *args)
        runtime·semrelease(&runtime·worldsema);
        runtime·starttheworld();
 
-       // give the queued finalizers, if any, a chance to run
-       if(finq != nil)
+       if(finq != nil) {
+               runtime·lock(&finlock);
+               // kick off or wake up goroutine to run queued finalizers
+               if(fing == nil)
+                       fing = runtime·newproc1(&runfinqv, nil, 0, 0, runtime·gc);
+               else if(fingwait) {
+                       fingwait = 0;
+                       runtime·ready(fing);
+               }
+               runtime·unlock(&finlock);
+               // give the queued finalizers, if any, a chance to run
                runtime·gosched();
+       }
 }
 
 void
@@ -2176,19 +2174,15 @@ runfinq(void)
        frame = nil;
        framecap = 0;
        for(;;) {
-               // There's no need for a lock in this section
-               // because it only conflicts with the garbage
-               // collector, and the garbage collector only
-               // runs when everyone else is stopped, and
-               // runfinq only stops at the gosched() or
-               // during the calls in the for loop.
+               runtime·lock(&finlock);
                fb = finq;
                finq = nil;
                if(fb == nil) {
                        fingwait = 1;
-                       runtime·park(nil, nil, "finalizer wait");
+                       runtime·park(runtime·unlock, &finlock, "finalizer wait");
                        continue;
                }
+               runtime·unlock(&finlock);
                if(raceenabled)
                        runtime·racefingo();
                for(; fb; fb=next) {