From 3d16e887967eb96476482a70da3b23d8234a1a4c Mon Sep 17 00:00:00 2001
From: ian <ian@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Fri, 21 Jan 2011 23:33:52 +0000
Subject: [PATCH] Avoid deadlock when finalizer lock is held during gc.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@169112 138bc75d-0d04-0410-961f-82ee72b054a4
---
 libgo/runtime/go-go.c   |  9 +++++++++
 libgo/runtime/mfinal.c  | 32 ++++++++++++++++++++++++++++++--
 libgo/runtime/runtime.h |  2 ++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/libgo/runtime/go-go.c b/libgo/runtime/go-go.c
index 112d52fced8..7c5f40de5ef 100644
--- a/libgo/runtime/go-go.c
+++ b/libgo/runtime/go-go.c
@@ -315,6 +315,15 @@ gc_stop_handler (int sig __attribute__ ((unused)))
       return;
     }
 
+  if (__sync_bool_compare_and_swap (&pm->holds_finlock, 1, 1))
+    {
+      /* Similarly, we can't interrupt the thread while it holds the
+	 finalizer lock.  Otherwise we can get into a deadlock when
+	 mark calls runtime_walkfintab.  */
+      __sync_bool_compare_and_swap (&pm->gcing_for_finlock, 0, 1);
+      return;
+    }
+
   stop_for_gc ();
 }
 
diff --git a/libgo/runtime/mfinal.c b/libgo/runtime/mfinal.c
index 5d32721e696..23c0d7a1663 100644
--- a/libgo/runtime/mfinal.c
+++ b/libgo/runtime/mfinal.c
@@ -106,9 +106,13 @@ runtime_addfinalizer(void *p, void (*f)(void*), const struct __go_func_type *ft)
 		e->ft = ft;
 	}
 
+	if(!__sync_bool_compare_and_swap(&m->holds_finlock, 0, 1))
+		runtime_throw("finalizer deadlock");
+
 	runtime_lock(&finlock);
 	if(!runtime_mlookup(p, &base, nil, nil, &ref) || p != base) {
 		runtime_unlock(&finlock);
+		__sync_bool_compare_and_swap(&m->holds_finlock, 1, 0);
 		runtime_throw("addfinalizer on invalid pointer");
 	}
 	if(f == nil) {
@@ -116,12 +120,12 @@ runtime_addfinalizer(void *p, void (*f)(void*), const struct __go_func_type *ft)
 			lookfintab(&fintab, p, 1);
 			*ref &= ~RefHasFinalizer;
 		}
-		runtime_unlock(&finlock);
-		return;
+		goto unlock;
 	}
 
 	if(*ref & RefHasFinalizer) {
 		runtime_unlock(&finlock);
+		__sync_bool_compare_and_swap(&m->holds_finlock, 1, 0);
 		runtime_throw("double finalizer");
 	}
 	*ref |= RefHasFinalizer;
@@ -156,7 +160,14 @@ runtime_addfinalizer(void *p, void (*f)(void*), const struct __go_func_type *ft)
 	}
 
 	addfintab(&fintab, p, e);
+ unlock:
 	runtime_unlock(&finlock);
+
+	__sync_bool_compare_and_swap(&m->holds_finlock, 1, 0);
+
+	if(__sync_bool_compare_and_swap(&m->gcing_for_finlock, 1, 0)) {
+		__go_run_goroutine_gc(200);
+	}
 }
 
 // get finalizer; if del, delete finalizer.
@@ -166,9 +177,18 @@ runtime_getfinalizer(void *p, bool del)
 {
 	Finalizer *f;
 	
+	if(!__sync_bool_compare_and_swap(&m->holds_finlock, 0, 1))
+		runtime_throw("finalizer deadlock");
+
 	runtime_lock(&finlock);
 	f = lookfintab(&fintab, p, del);
 	runtime_unlock(&finlock);
+
+	__sync_bool_compare_and_swap(&m->holds_finlock, 1, 0);
+	if(__sync_bool_compare_and_swap(&m->gcing_for_finlock, 1, 0)) {
+		__go_run_goroutine_gc(201);
+	}
+
 	return f;
 }
 
@@ -178,6 +198,9 @@ runtime_walkfintab(void (*fn)(void*), void (*scan)(byte *, int64))
 	void **key;
 	void **ekey;
 
+	if(!__sync_bool_compare_and_swap(&m->holds_finlock, 0, 1))
+		runtime_throw("finalizer deadlock");
+
 	scan((byte*)&fintab, sizeof fintab);
 	runtime_lock(&finlock);
 	key = fintab.key;
@@ -186,4 +209,9 @@ runtime_walkfintab(void (*fn)(void*), void (*scan)(byte *, int64))
 		if(*key != nil && *key != ((void*)-1))
 			fn(*key);
 	runtime_unlock(&finlock);
+
+	__sync_bool_compare_and_swap(&m->holds_finlock, 1, 0);
+	if(__sync_bool_compare_and_swap(&m->gcing_for_finlock, 1, 0)) {
+		runtime_throw("walkfintab not called from gc");
+	}
 }
diff --git a/libgo/runtime/runtime.h b/libgo/runtime/runtime.h
index 3027f0c42d2..e43177fef59 100644
--- a/libgo/runtime/runtime.h
+++ b/libgo/runtime/runtime.h
@@ -97,6 +97,8 @@ struct	M
 	int32	locks;
 	int32	nomemprof;
 	int32	gcing_for_prof;
+	int32	holds_finlock;
+	int32	gcing_for_finlock;
 	MCache	*mcache;
 
 	/* For the list of all threads.  */
-- 
2.11.0