binder: add spinlock to protect binder_node

node->node_lock is used to protect elements of node. No
need to acquire for fields that are invariant: debug_id,
ptr, cookie.

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 165 insertions, 55 deletions

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 5a0389767843..5654187555be 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -318,6 +318,7 @@ struct binder_error {
  * @proc:                 binder_proc that owns this node
  *                        (invariant after initialized)
  * @refs:                 list of references on this node
+ *                        (protected by @lock)
  * @internal_strong_refs: used to take strong references when
  *                        initiating a transaction
  *                        (protected by @proc->inner_lock if @proc
@@ -351,6 +352,7 @@ struct binder_error {
  *                        (protected by @proc->inner_lock if @proc
  *                        and by @lock)
  * @has_async_transaction: async transaction to node in progress
+ *                        (protected by @lock)
  * @accept_fds:           file descriptor operations supported for node
  *                        (invariant after initialized)
  * @min_priority:         minimum scheduling priority
@@ -432,6 +434,7 @@ struct binder_ref_data {
  * @rb_node_desc: node for lookup by @data.desc in proc's rb_tree
  * @rb_node_node: node for lookup by @node in proc's rb_tree
  * @node_entry:  list entry for node->refs list in target node
+ *               (protected by @node->lock)
  * @proc:        binder_proc containing ref
  * @node:        binder_node of target node. When cleaning up a
  *               ref for deletion in binder_cleanup_ref, a non-NULL
@@ -707,6 +710,43 @@ _binder_node_unlock(struct binder_node *node, int line)
 	spin_unlock(&node->lock);
 }
 
+/**
+ * binder_node_inner_lock() - Acquire node and inner locks
+ * @node:         struct binder_node to acquire
+ *
+ * Acquires node->lock. If node->proc also acquires
+ * proc->inner_lock. Used to protect binder_node fields
+ */
+#define binder_node_inner_lock(node) _binder_node_inner_lock(node, __LINE__)
+static void
+_binder_node_inner_lock(struct binder_node *node, int line)
+{
+	binder_debug(BINDER_DEBUG_SPINLOCKS,
+		     "%s: line=%d\n", __func__, line);
+	spin_lock(&node->lock);
+	if (node->proc)
+		binder_inner_proc_lock(node->proc);
+}
+
+/**
+ * binder_node_unlock() - Release node and inner locks
+ * @node:         struct binder_node to acquire
+ *
+ * Release lock acquired via binder_node_lock()
+ */
+#define binder_node_inner_unlock(node) _binder_node_inner_unlock(node, __LINE__)
+static void
+_binder_node_inner_unlock(struct binder_node *node, int line)
+{
+	struct binder_proc *proc = node->proc;
+
+	binder_debug(BINDER_DEBUG_SPINLOCKS,
+		     "%s: line=%d\n", __func__, line);
+	if (proc)
+		binder_inner_proc_unlock(proc);
+	spin_unlock(&node->lock);
+}
+
 static bool binder_worklist_empty_ilocked(struct list_head *list)
 {
 	return list_empty(list);
@@ -925,12 +965,14 @@ static struct binder_node *binder_get_node(struct binder_proc *proc,
 }
 
 static struct binder_node *binder_new_node(struct binder_proc *proc,
-					   binder_uintptr_t ptr,
-					   binder_uintptr_t cookie)
+					   struct flat_binder_object *fp)
 {
 	struct rb_node **p = &proc->nodes.rb_node;
 	struct rb_node *parent = NULL;
 	struct binder_node *node;
+	binder_uintptr_t ptr = fp ? fp->binder : 0;
+	binder_uintptr_t cookie = fp ? fp->cookie : 0;
+	__u32 flags = fp ? fp->flags : 0;
 
 	while (*p) {
 		parent = *p;
@@ -956,6 +998,8 @@ static struct binder_node *binder_new_node(struct binder_proc *proc,
 	node->ptr = ptr;
 	node->cookie = cookie;
 	node->work.type = BINDER_WORK_NODE;
+	node->min_priority = flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
+	node->accept_fds = !!(flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
 	spin_lock_init(&node->lock);
 	INIT_LIST_HEAD(&node->work.entry);
 	INIT_LIST_HEAD(&node->async_todo);
@@ -972,12 +1016,15 @@ static void binder_free_node(struct binder_node *node)
 	binder_stats_deleted(BINDER_STAT_NODE);
 }
 
-static int binder_inc_node_ilocked(struct binder_node *node, int strong,
-				   int internal,
-				   struct list_head *target_list)
+static int binder_inc_node_nilocked(struct binder_node *node, int strong,
+				    int internal,
+				    struct list_head *target_list)
 {
-	if (node->proc)
-		BUG_ON(!spin_is_locked(&node->proc->inner_lock));
+	struct binder_proc *proc = node->proc;
+
+	BUG_ON(!spin_is_locked(&node->lock));
+	if (proc)
+		BUG_ON(!spin_is_locked(&proc->inner_lock));
 	if (strong) {
 		if (internal) {
 			if (target_list == NULL &&
@@ -1016,20 +1063,19 @@ static int binder_inc_node(struct binder_node *node, int strong, int internal,
 {
 	int ret;
 
-	if (node->proc)
-		binder_inner_proc_lock(node->proc);
-	ret = binder_inc_node_ilocked(node, strong, internal, target_list);
-	if (node->proc)
-		binder_inner_proc_unlock(node->proc);
+	binder_node_inner_lock(node);
+	ret = binder_inc_node_nilocked(node, strong, internal, target_list);
+	binder_node_inner_unlock(node);
 
 	return ret;
 }
 
-static bool binder_dec_node_ilocked(struct binder_node *node,
-				    int strong, int internal)
+static bool binder_dec_node_nilocked(struct binder_node *node,
+				     int strong, int internal)
 {
 	struct binder_proc *proc = node->proc;
 
+	BUG_ON(!spin_is_locked(&node->lock));
 	if (proc)
 		BUG_ON(!spin_is_locked(&proc->inner_lock));
 	if (strong) {
@@ -1088,12 +1134,9 @@ static void binder_dec_node(struct binder_node *node, int strong, int internal)
 {
 	bool free_node;
 
-	if (node->proc)
-		binder_inner_proc_lock(node->proc);
-	free_node = binder_dec_node_ilocked(node, strong, internal);
-	if (node->proc)
-		binder_inner_proc_unlock(node->proc);
-
+	binder_node_inner_lock(node);
+	free_node = binder_dec_node_nilocked(node, strong, internal);
+	binder_node_inner_unlock(node);
 	if (free_node)
 		binder_free_node(node);
 }
@@ -1123,6 +1166,7 @@ static void binder_inc_node_tmpref_ilocked(struct binder_node *node)
  */
 static void binder_inc_node_tmpref(struct binder_node *node)
 {
+	binder_node_lock(node);
 	if (node->proc)
 		binder_inner_proc_lock(node->proc);
 	else
@@ -1132,6 +1176,7 @@ static void binder_inc_node_tmpref(struct binder_node *node)
 		binder_inner_proc_unlock(node->proc);
 	else
 		spin_unlock(&binder_dead_nodes_lock);
+	binder_node_unlock(node);
 }
 
 /**
@@ -1144,9 +1189,8 @@ static void binder_dec_node_tmpref(struct binder_node *node)
 {
 	bool free_node;
 
-	if (node->proc)
-		binder_inner_proc_lock(node->proc);
-	else
+	binder_node_inner_lock(node);
+	if (!node->proc)
 		spin_lock(&binder_dead_nodes_lock);
 	node->tmp_refs--;
 	BUG_ON(node->tmp_refs < 0);
@@ -1158,9 +1202,8 @@ static void binder_dec_node_tmpref(struct binder_node *node)
 	 * causes no actual reference to be released in binder_dec_node().
 	 * If that changes, a change is needed here too.
 	 */
-	free_node = binder_dec_node_ilocked(node, 0, 1);
-	if (node->proc)
-		binder_inner_proc_unlock(node->proc);
+	free_node = binder_dec_node_nilocked(node, 0, 1);
+	binder_node_inner_unlock(node);
 	if (free_node)
 		binder_free_node(node);
 }
@@ -1264,19 +1307,21 @@ static struct binder_ref *binder_get_ref_for_node(struct binder_proc *proc,
 	}
 	rb_link_node(&new_ref->rb_node_desc, parent, p);
 	rb_insert_color(&new_ref->rb_node_desc, &proc->refs_by_desc);
+
+	binder_node_lock(node);
 	hlist_add_head(&new_ref->node_entry, &node->refs);
 
 	binder_debug(BINDER_DEBUG_INTERNAL_REFS,
 		     "%d new ref %d desc %d for node %d\n",
 		      proc->pid, new_ref->data.debug_id, new_ref->data.desc,
 		      node->debug_id);
+	binder_node_unlock(node);
 	return new_ref;
 }
 
 static void binder_cleanup_ref(struct binder_ref *ref)
 {
 	bool delete_node = false;
-	struct binder_proc *node_proc = ref->node->proc;
 
 	binder_debug(BINDER_DEBUG_INTERNAL_REFS,
 		     "%d delete ref %d desc %d for node %d\n",
@@ -1286,15 +1331,13 @@ static void binder_cleanup_ref(struct binder_ref *ref)
 	rb_erase(&ref->rb_node_desc, &ref->proc->refs_by_desc);
 	rb_erase(&ref->rb_node_node, &ref->proc->refs_by_node);
 
-	if (node_proc)
-		binder_inner_proc_lock(node_proc);
+	binder_node_inner_lock(ref->node);
 	if (ref->data.strong)
-		binder_dec_node_ilocked(ref->node, 1, 1);
+		binder_dec_node_nilocked(ref->node, 1, 1);
 
 	hlist_del(&ref->node_entry);
-	delete_node = binder_dec_node_ilocked(ref->node, 0, 1);
-	if (node_proc)
-		binder_inner_proc_unlock(node_proc);
+	delete_node = binder_dec_node_nilocked(ref->node, 0, 1);
+	binder_node_inner_unlock(ref->node);
 	/*
 	 * Clear ref->node unless we want the caller to free the node
 	 */
@@ -1989,12 +2032,9 @@ static int binder_translate_binder(struct flat_binder_object *fp,
 
 	node = binder_get_node(proc, fp->binder);
 	if (!node) {
-		node = binder_new_node(proc, fp->binder, fp->cookie);
+		node = binder_new_node(proc, fp);
 		if (!node)
 			return -ENOMEM;
-
-		node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
-		node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
 	}
 	if (fp->cookie != node->cookie) {
 		binder_user_error("%d:%d sending u%016llx node %d, cookie mismatch %016llx != %016llx\n",
@@ -2055,6 +2095,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
 		goto done;
 	}
 
+	binder_node_lock(node);
 	if (node->proc == target_proc) {
 		if (fp->hdr.type == BINDER_TYPE_HANDLE)
 			fp->hdr.type = BINDER_TYPE_BINDER;
@@ -2062,18 +2103,24 @@ static int binder_translate_handle(struct flat_binder_object *fp,
 			fp->hdr.type = BINDER_TYPE_WEAK_BINDER;
 		fp->binder = node->ptr;
 		fp->cookie = node->cookie;
-		binder_inc_node(node,
-				fp->hdr.type == BINDER_TYPE_BINDER,
-				0, NULL);
+		if (node->proc)
+			binder_inner_proc_lock(node->proc);
+		binder_inc_node_nilocked(node,
+					 fp->hdr.type == BINDER_TYPE_BINDER,
+					 0, NULL);
+		if (node->proc)
+			binder_inner_proc_unlock(node->proc);
 		trace_binder_transaction_ref_to_node(t, node, &src_rdata);
 		binder_debug(BINDER_DEBUG_TRANSACTION,
 			     "        ref %d desc %d -> node %d u%016llx\n",
 			     src_rdata.debug_id, src_rdata.desc, node->debug_id,
 			     (u64)node->ptr);
+		binder_node_unlock(node);
 	} else {
 		int ret;
 		struct binder_ref_data dest_rdata;
 
+		binder_node_unlock(node);
 		ret = binder_inc_ref_for_node(target_proc, node,
 				fp->hdr.type == BINDER_TYPE_HANDLE,
 				NULL, &dest_rdata);
@@ -2381,13 +2428,16 @@ static void binder_transaction(struct binder_proc *proc,
 			mutex_unlock(&context->context_mgr_node_lock);
 		}
 		e->to_node = target_node->debug_id;
+		binder_node_lock(target_node);
 		target_proc = target_node->proc;
 		if (target_proc == NULL) {
+			binder_node_unlock(target_node);
 			return_error = BR_DEAD_REPLY;
 			return_error_line = __LINE__;
 			goto err_dead_binder;
 		}
 		target_proc->tmp_ref++;
+		binder_node_unlock(target_node);
 		if (security_binder_transaction(proc->tsk,
 						target_proc->tsk) < 0) {
 			return_error = BR_FAILED_REPLY;
@@ -2704,6 +2754,7 @@ static void binder_transaction(struct binder_proc *proc,
 	}
 	tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
 	binder_enqueue_work(proc, tcomplete, &thread->todo);
+	t->work.type = BINDER_WORK_TRANSACTION;
 
 	if (reply) {
 		if (target_thread->is_dead)
@@ -2711,6 +2762,7 @@ static void binder_transaction(struct binder_proc *proc,
 		BUG_ON(t->buffer->async_transaction != 0);
 		binder_pop_transaction(target_thread, in_reply_to);
 		binder_free_transaction(in_reply_to);
+		binder_enqueue_work(target_proc, &t->work, target_list);
 	} else if (!(t->flags & TF_ONE_WAY)) {
 		BUG_ON(t->buffer->async_transaction != 0);
 		t->need_reply = 1;
@@ -2721,20 +2773,29 @@ static void binder_transaction(struct binder_proc *proc,
 			binder_pop_transaction(thread, t);
 			goto err_dead_proc_or_thread;
 		}
+		binder_enqueue_work(target_proc, &t->work, target_list);
 	} else {
 		BUG_ON(target_node == NULL);
 		BUG_ON(t->buffer->async_transaction != 1);
+		binder_node_lock(target_node);
 		if (target_node->has_async_transaction) {
 			target_list = &target_node->async_todo;
 			target_wait = NULL;
 		} else
 			target_node->has_async_transaction = 1;
+		/*
+		 * Test/set of has_async_transaction
+		 * must be atomic with enqueue on
+		 * async_todo
+		 */
 		if (target_proc->is_dead ||
-				(target_thread && target_thread->is_dead))
+				(target_thread && target_thread->is_dead)) {
+			binder_node_unlock(target_node);
 			goto err_dead_proc_or_thread;
+		}
+		binder_enqueue_work(target_proc, &t->work, target_list);
+		binder_node_unlock(target_node);
 	}
-	t->work.type = BINDER_WORK_TRANSACTION;
-	binder_enqueue_work(target_proc, &t->work, target_list);
 	if (target_wait) {
 		if (reply || !(tr->flags & TF_ONE_WAY))
 			wake_up_interruptible_sync(target_wait);
@@ -2913,6 +2974,7 @@ static int binder_thread_write(struct binder_proc *proc,
 			binder_uintptr_t node_ptr;
 			binder_uintptr_t cookie;
 			struct binder_node *node;
+			bool free_node;
 
 			if (get_user(node_ptr, (binder_uintptr_t __user *)ptr))
 				return -EFAULT;
@@ -2940,13 +3002,13 @@ static int binder_thread_write(struct binder_proc *proc,
 				binder_put_node(node);
 				break;
 			}
-			binder_inner_proc_lock(proc);
+			binder_node_inner_lock(node);
 			if (cmd == BC_ACQUIRE_DONE) {
 				if (node->pending_strong_ref == 0) {
 					binder_user_error("%d:%d BC_ACQUIRE_DONE node %d has no pending acquire request\n",
 						proc->pid, thread->pid,
 						node->debug_id);
-					binder_inner_proc_unlock(proc);
+					binder_node_inner_unlock(node);
 					binder_put_node(node);
 					break;
 				}
@@ -2956,20 +3018,22 @@ static int binder_thread_write(struct binder_proc *proc,
 					binder_user_error("%d:%d BC_INCREFS_DONE node %d has no pending increfs request\n",
 						proc->pid, thread->pid,
 						node->debug_id);
-					binder_inner_proc_unlock(proc);
+					binder_node_inner_unlock(node);
 					binder_put_node(node);
 					break;
 				}
 				node->pending_weak_ref = 0;
 			}
-			binder_inner_proc_unlock(proc);
-			binder_dec_node(node, cmd == BC_ACQUIRE_DONE, 0);
+			free_node = binder_dec_node_nilocked(node,
+					cmd == BC_ACQUIRE_DONE, 0);
+			WARN_ON(free_node);
 			binder_debug(BINDER_DEBUG_USER_REFS,
 				     "%d:%d %s node %d ls %d lw %d tr %d\n",
 				     proc->pid, thread->pid,
 				     cmd == BC_INCREFS_DONE ? "BC_INCREFS_DONE" : "BC_ACQUIRE_DONE",
 				     node->debug_id, node->local_strong_refs,
 				     node->local_weak_refs, node->tmp_refs);
+			binder_node_inner_unlock(node);
 			binder_put_node(node);
 			break;
 		}
@@ -3015,9 +3079,9 @@ static int binder_thread_write(struct binder_proc *proc,
 				struct binder_work *w;
 
 				buf_node = buffer->target_node;
+				binder_node_inner_lock(buf_node);
 				BUG_ON(!buf_node->has_async_transaction);
 				BUG_ON(buf_node->proc != proc);
-				binder_inner_proc_lock(proc);
 				w = binder_dequeue_work_head_ilocked(
 						&buf_node->async_todo);
 				if (!w)
@@ -3025,7 +3089,7 @@ static int binder_thread_write(struct binder_proc *proc,
 				else
 					binder_enqueue_work_ilocked(
 							w, &thread->todo);
-				binder_inner_proc_unlock(proc);
+				binder_node_inner_unlock(buf_node);
 			}
 			trace_binder_transaction_buffer_release(buffer);
 			binder_transaction_buffer_release(proc, buffer, NULL);
@@ -3150,6 +3214,7 @@ static int binder_thread_write(struct binder_proc *proc,
 				INIT_LIST_HEAD(&death->work.entry);
 				death->cookie = cookie;
 				ref->death = death;
+				binder_node_lock(ref->node);
 				if (ref->node->proc == NULL) {
 					ref->death->work.type = BINDER_WORK_DEAD_BINDER;
 					if (thread->looper &
@@ -3168,10 +3233,13 @@ static int binder_thread_write(struct binder_proc *proc,
 								&proc->wait);
 					}
 				}
+				binder_node_unlock(ref->node);
 			} else {
+				binder_node_lock(ref->node);
 				if (ref->death == NULL) {
 					binder_user_error("%d:%d BC_CLEAR_DEATH_NOTIFICATION death notification not active\n",
 						proc->pid, thread->pid);
+					binder_node_unlock(ref->node);
 					break;
 				}
 				death = ref->death;
@@ -3180,6 +3248,7 @@ static int binder_thread_write(struct binder_proc *proc,
 						proc->pid, thread->pid,
 						(u64)death->cookie,
 						(u64)cookie);
+					binder_node_unlock(ref->node);
 					break;
 				}
 				ref->death = NULL;
@@ -3204,6 +3273,7 @@ static int binder_thread_write(struct binder_proc *proc,
 					death->work.type = BINDER_WORK_DEAD_BINDER_AND_CLEAR;
 				}
 				binder_inner_proc_unlock(proc);
+				binder_node_unlock(ref->node);
 			}
 		} break;
 		case BC_DEAD_BINDER_DONE: {
@@ -3486,6 +3556,17 @@ retry:
 					     (u64)node_cookie);
 				rb_erase(&node->rb_node, &proc->nodes);
 				binder_inner_proc_unlock(proc);
+				binder_node_lock(node);
+				/*
+				 * Acquire the node lock before freeing the
+				 * node to serialize with other threads that
+				 * may have been holding the node lock while
+				 * decrementing this node (avoids race where
+				 * this thread frees while the other thread
+				 * is unlocking the node after the final
+				 * decrement)
+				 */
+				binder_node_unlock(node);
 				binder_free_node(node);
 			} else
 				binder_inner_proc_unlock(proc);
@@ -3973,16 +4054,18 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
 	} else {
 		context->binder_context_mgr_uid = curr_euid;
 	}
-	new_node = binder_new_node(proc, 0, 0);
+	new_node = binder_new_node(proc, NULL);
 	if (!new_node) {
 		ret = -ENOMEM;
 		goto out;
 	}
+	binder_node_lock(new_node);
 	new_node->local_weak_refs++;
 	new_node->local_strong_refs++;
 	new_node->has_strong_ref = 1;
 	new_node->has_weak_ref = 1;
 	context->binder_context_mgr_node = new_node;
+	binder_node_unlock(new_node);
 	binder_put_node(new_node);
 out:
 	mutex_unlock(&context->context_mgr_node_lock);
@@ -4245,6 +4328,7 @@ static int binder_node_release(struct binder_node *node, int refs)
 
 	binder_release_work(proc, &node->async_todo);
 
+	binder_node_lock(node);
 	binder_inner_proc_lock(proc);
 	binder_dequeue_work_ilocked(&node->work);
 	/*
@@ -4253,6 +4337,7 @@ static int binder_node_release(struct binder_node *node, int refs)
 	BUG_ON(!node->tmp_refs);
 	if (hlist_empty(&node->refs) && node->tmp_refs == 1) {
 		binder_inner_proc_unlock(proc);
+		binder_node_unlock(node);
 		binder_free_node(node);
 
 		return refs;
@@ -4289,6 +4374,7 @@ static int binder_node_release(struct binder_node *node, int refs)
 	binder_debug(BINDER_DEBUG_DEAD_BINDER,
 		     "node %d now dead, refs %d, death %d\n",
 		     node->debug_id, refs, death);
+	binder_node_unlock(node);
 	binder_put_node(node);
 
 	return refs;
@@ -4532,12 +4618,15 @@ static void print_binder_thread_ilocked(struct seq_file *m,
 		m->count = start_pos;
 }
 
-static void print_binder_node(struct seq_file *m, struct binder_node *node)
+static void print_binder_node_nlocked(struct seq_file *m,
+				      struct binder_node *node)
 {
 	struct binder_ref *ref;
 	struct binder_work *w;
 	int count;
 
+	WARN_ON(!spin_is_locked(&node->lock));
+
 	count = 0;
 	hlist_for_each_entry(ref, &node->refs, node_entry)
 		count++;
@@ -4564,11 +4653,13 @@ static void print_binder_node(struct seq_file *m, struct binder_node *node)
 
 static void print_binder_ref(struct seq_file *m, struct binder_ref *ref)
 {
+	binder_node_lock(ref->node);
 	seq_printf(m, "  ref %d: desc %d %snode %d s %d w %d d %pK\n",
 		   ref->data.debug_id, ref->data.desc,
 		   ref->node->proc ? "" : "dead ",
 		   ref->node->debug_id, ref->data.strong,
 		   ref->data.weak, ref->death);
+	binder_node_unlock(ref->node);
 }
 
 static void print_binder_proc(struct seq_file *m,
@@ -4591,8 +4682,10 @@ static void print_binder_proc(struct seq_file *m,
 	for (n = rb_first(&proc->nodes); n != NULL; n = rb_next(n)) {
 		struct binder_node *node = rb_entry(n, struct binder_node,
 						    rb_node);
+		binder_node_lock(node);
 		if (print_all || node->has_async_transaction)
-			print_binder_node(m, node);
+			print_binder_node_nlocked(m, node);
+		binder_node_unlock(node);
 	}
 	if (print_all) {
 		for (n = rb_first(&proc->refs_by_desc);
@@ -4764,6 +4857,7 @@ static int binder_state_show(struct seq_file *m, void *unused)
 {
 	struct binder_proc *proc;
 	struct binder_node *node;
+	struct binder_node *last_node = NULL;
 
 	binder_lock(__func__);
 
@@ -4772,9 +4866,25 @@ static int binder_state_show(struct seq_file *m, void *unused)
 	spin_lock(&binder_dead_nodes_lock);
 	if (!hlist_empty(&binder_dead_nodes))
 		seq_puts(m, "dead nodes:\n");
-	hlist_for_each_entry(node, &binder_dead_nodes, dead_node)
-		print_binder_node(m, node);
+	hlist_for_each_entry(node, &binder_dead_nodes, dead_node) {
+		/*
+		 * take a temporary reference on the node so it
+		 * survives and isn't removed from the list
+		 * while we print it.
+		 */
+		node->tmp_refs++;
+		spin_unlock(&binder_dead_nodes_lock);
+		if (last_node)
+			binder_put_node(last_node);
+		binder_node_lock(node);
+		print_binder_node_nlocked(m, node);
+		binder_node_unlock(node);
+		last_node = node;
+		spin_lock(&binder_dead_nodes_lock);
+	}
 	spin_unlock(&binder_dead_nodes_lock);
+	if (last_node)
+		binder_put_node(last_node);
 
 	mutex_lock(&binder_procs_lock);
 	hlist_for_each_entry(proc, &binder_procs, proc_node)