code review 12371043: runtime: remove debugging knob to turn off preemption

src/pkg/runtime/proc.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.
 
 #include "runtime.h"
 #include "arch_GOARCH.h"
 #include "malloc.h"
 #include "stack.h"
 #include "race.h"
 #include "type.h"
@@ skipping 2253 matching lines @@
 // goroutine.  It can send inform the wrong goroutine.  Even if it informs the
 // correct goroutine, that goroutine might ignore the request if it is
 // simultaneously executing runtime·newstack.
 // No lock needs to be held.
 static void
 preemptone(P *p)
 {
         M *mp;
         G *gp;
 
-// Preemption requires more robust traceback routines.
-// For now, disable.
-// The if(1) silences a compiler warning about the rest of the
-// function being unreachable.
-if(0) return;
-
         mp = p->m;
         if(mp == nil || mp == m)
                 return;
         gp = mp->curg;
         if(gp == nil || gp == mp->g0)
                 return;
         gp->preempt = true;
         gp->stackguard0 = StackPreempt;
 }
 
@@ skipping 309 matching lines @@
 bool
 runtime·topofstack(Func *f)
 {
         return f->entry == (uintptr)runtime·goexit ||
                 f->entry == (uintptr)runtime·mstart ||
                 f->entry == (uintptr)runtime·mcall ||
                 f->entry == (uintptr)runtime·morestack ||
                 f->entry == (uintptr)runtime·lessstack ||
                 f->entry == (uintptr)_rt0_go;
 }