binder: refactor queue management in binder_thread_read

In binder_thread_read, the BINDER_WORK_NODE command is used
to communicate the references on the node to userspace. It
can take a couple of iterations in the loop to construct
the list of commands for user space. When locking is added,
the lock would need to be release on each iteration which
means the state could change. The work item is not dequeued
during this process which prevents a simpler queue management
that can just dequeue up front and handle the work item.

Fixed by changing the BINDER_WORK_NODE algorithm in
binder_thread_read to determine which commands to send
to userspace atomically in 1 pass so it stays consistent
with the kernel view.

The work item is now dequeued immediately since only
1 pass is needed.
Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -2285,6 +2285,37 @@ static int binder_has_thread_work(struct binder_thread *thread)
 		(thread->looper & BINDER_LOOPER_STATE_NEED_RETURN);
 }
 
+static int binder_put_node_cmd(struct binder_proc *proc,
+			       struct binder_thread *thread,
+			       void __user **ptrp,
+			       binder_uintptr_t node_ptr,
+			       binder_uintptr_t node_cookie,
+			       int node_debug_id,
+			       uint32_t cmd, const char *cmd_name)
+{
+	void __user *ptr = *ptrp;
+
+	if (put_user(cmd, (uint32_t __user *)ptr))
+		return -EFAULT;
+	ptr += sizeof(uint32_t);
+
+	if (put_user(node_ptr, (binder_uintptr_t __user *)ptr))
+		return -EFAULT;
+	ptr += sizeof(binder_uintptr_t);
+
+	if (put_user(node_cookie, (binder_uintptr_t __user *)ptr))
+		return -EFAULT;
+	ptr += sizeof(binder_uintptr_t);
+
+	binder_stat_br(proc, thread, cmd);
+	binder_debug(BINDER_DEBUG_USER_REFS, "%d:%d %s %d u%016llx c%016llx\n",
+		     proc->pid, thread->pid, cmd_name, node_debug_id,
+		     (u64)node_ptr, (u64)node_cookie);
+
+	*ptrp = ptr;
+	return 0;
+}
+
 static int binder_thread_read(struct binder_proc *proc,
 			      struct binder_thread *thread,
 			      binder_uintptr_t binder_buffer, size_t size,
@@ -2410,72 +2441,78 @@ static int binder_thread_read(struct binder_proc *proc,
 		} break;
 		case BINDER_WORK_NODE: {
 			struct binder_node *node = container_of(w, struct binder_node, work);
-			uint32_t cmd = BR_NOOP;
-			const char *cmd_name;
-			int strong = node->internal_strong_refs || node->local_strong_refs;
-			int weak = !hlist_empty(&node->refs) || node->local_weak_refs || strong;
-
-			if (weak && !node->has_weak_ref) {
-				cmd = BR_INCREFS;
-				cmd_name = "BR_INCREFS";
+			int strong, weak;
+			binder_uintptr_t node_ptr = node->ptr;
+			binder_uintptr_t node_cookie = node->cookie;
+			int node_debug_id = node->debug_id;
+			int has_weak_ref;
+			int has_strong_ref;
+			void __user *orig_ptr = ptr;
+
+			BUG_ON(proc != node->proc);
+			strong = node->internal_strong_refs ||
+					node->local_strong_refs;
+			weak = !hlist_empty(&node->refs) ||
+					node->local_weak_refs || strong;
+			has_strong_ref = node->has_strong_ref;
+			has_weak_ref = node->has_weak_ref;
+
+			if (weak && !has_weak_ref) {
 				node->has_weak_ref = 1;
 				node->pending_weak_ref = 1;
 				node->local_weak_refs++;
-			} else if (strong && !node->has_strong_ref) {
-				cmd = BR_ACQUIRE;
-				cmd_name = "BR_ACQUIRE";
+			}
+			if (strong && !has_strong_ref) {
 				node->has_strong_ref = 1;
 				node->pending_strong_ref = 1;
 				node->local_strong_refs++;
-			} else if (!strong && node->has_strong_ref) {
-				cmd = BR_RELEASE;
-				cmd_name = "BR_RELEASE";
+			}
+			if (!strong && has_strong_ref)
 				node->has_strong_ref = 0;
-			} else if (!weak && node->has_weak_ref) {
-				cmd = BR_DECREFS;
-				cmd_name = "BR_DECREFS";
+			if (!weak && has_weak_ref)
 				node->has_weak_ref = 0;
+			list_del(&w->entry);
+
+			if (!weak && !strong) {
+				binder_debug(BINDER_DEBUG_INTERNAL_REFS,
+					     "%d:%d node %d u%016llx c%016llx deleted\n",
+					     proc->pid, thread->pid,
+					     node_debug_id,
+					     (u64)node_ptr,
+					     (u64)node_cookie);
+				rb_erase(&node->rb_node, &proc->nodes);
+				kfree(node);
+				binder_stats_deleted(BINDER_STAT_NODE);
 			}
-			if (cmd != BR_NOOP) {
-				if (put_user(cmd, (uint32_t __user *)ptr))
-					return -EFAULT;
-				ptr += sizeof(uint32_t);
-				if (put_user(node->ptr,
-					     (binder_uintptr_t __user *)ptr))
-					return -EFAULT;
-				ptr += sizeof(binder_uintptr_t);
-				if (put_user(node->cookie,
-					     (binder_uintptr_t __user *)ptr))
-					return -EFAULT;
-				ptr += sizeof(binder_uintptr_t);
-
-				binder_stat_br(proc, thread, cmd);
-				binder_debug(BINDER_DEBUG_USER_REFS,
-					     "%d:%d %s %d u%016llx c%016llx\n",
-					     proc->pid, thread->pid, cmd_name,
-					     node->debug_id,
-					     (u64)node->ptr, (u64)node->cookie);
-			} else {
-				list_del_init(&w->entry);
-				if (!weak && !strong) {
-					binder_debug(BINDER_DEBUG_INTERNAL_REFS,
-						     "%d:%d node %d u%016llx c%016llx deleted\n",
-						     proc->pid, thread->pid,
-						     node->debug_id,
-						     (u64)node->ptr,
-						     (u64)node->cookie);
-					rb_erase(&node->rb_node, &proc->nodes);
-					kfree(node);
-					binder_stats_deleted(BINDER_STAT_NODE);
-				} else {
-					binder_debug(BINDER_DEBUG_INTERNAL_REFS,
-						     "%d:%d node %d u%016llx c%016llx state unchanged\n",
-						     proc->pid, thread->pid,
-						     node->debug_id,
-						     (u64)node->ptr,
-						     (u64)node->cookie);
-				}
-			}
+			if (weak && !has_weak_ref)
+				ret = binder_put_node_cmd(
+						proc, thread, &ptr, node_ptr,
+						node_cookie, node_debug_id,
+						BR_INCREFS, "BR_INCREFS");
+			if (!ret && strong && !has_strong_ref)
+				ret = binder_put_node_cmd(
+						proc, thread, &ptr, node_ptr,
+						node_cookie, node_debug_id,
+						BR_ACQUIRE, "BR_ACQUIRE");
+			if (!ret && !strong && has_strong_ref)
+				ret = binder_put_node_cmd(
+						proc, thread, &ptr, node_ptr,
+						node_cookie, node_debug_id,
+						BR_RELEASE, "BR_RELEASE");
+			if (!ret && !weak && has_weak_ref)
+				ret = binder_put_node_cmd(
+						proc, thread, &ptr, node_ptr,
+						node_cookie, node_debug_id,
+						BR_DECREFS, "BR_DECREFS");
+			if (orig_ptr == ptr)
+				binder_debug(BINDER_DEBUG_INTERNAL_REFS,
+					     "%d:%d node %d u%016llx c%016llx state unchanged\n",
+					     proc->pid, thread->pid,
+					     node_debug_id,
+					     (u64)node_ptr,
+					     (u64)node_cookie);
+			if (ret)
+				return ret;
 		} break;
 		case BINDER_WORK_DEAD_BINDER:
 		case BINDER_WORK_DEAD_BINDER_AND_CLEAR: