binder: return pending info for frozen async txns

An async transaction to a frozen process will still be successfully
put in the queue. But this pending async transaction won't be processed
until the target process is unfrozen at an unspecified time in the
future. Pass this important information back to the user space caller
by returning BR_TRANSACTION_PENDING_FROZEN.

Signed-off-by: Li Li <[e-mail]>
Acked-by: Carlos Llamas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/android/binder.c

···
  *
  * Return:	0 if the transaction was successfully queued
  *		BR_DEAD_REPLY if the target process or thread is dead
- *		BR_FROZEN_REPLY if the target process or thread is frozen
+ *		BR_FROZEN_REPLY if the target process or thread is frozen and
+ *			the sync transaction was rejected
+ *		BR_TRANSACTION_PENDING_FROZEN if the target process is frozen
+ *		and the async transaction was successfully queued
  */
 static int binder_proc_transaction(struct binder_transaction *t,
 				    struct binder_proc *proc,
···
 	bool oneway = !!(t->flags & TF_ONE_WAY);
 	bool pending_async = false;
 	struct binder_transaction *t_outdated = NULL;
+	bool frozen = false;
 
 	BUG_ON(!node);
 	binder_node_lock(node);
···
 
 	binder_inner_proc_lock(proc);
 	if (proc->is_frozen) {
+		frozen = true;
 		proc->sync_recv |= !oneway;
 		proc->async_recv |= oneway;
 	}
 
-	if ((proc->is_frozen && !oneway) || proc->is_dead ||
+	if ((frozen && !oneway) || proc->is_dead ||
 			(thread && thread->is_dead)) {
 		binder_inner_proc_unlock(proc);
 		binder_node_unlock(node);
-		return proc->is_frozen ? BR_FROZEN_REPLY : BR_DEAD_REPLY;
+		return frozen ? BR_FROZEN_REPLY : BR_DEAD_REPLY;
 	}
 
 	if (!thread && !pending_async)
···
 	} else if (!pending_async) {
 		binder_enqueue_work_ilocked(&t->work, &proc->todo);
 	} else {
-		if ((t->flags & TF_UPDATE_TXN) && proc->is_frozen) {
+		if ((t->flags & TF_UPDATE_TXN) && frozen) {
 			t_outdated = binder_find_outdated_transaction_ilocked(t,
 									      &node->async_todo);
 			if (t_outdated) {
···
 		kfree(t_outdated);
 		binder_stats_deleted(BINDER_STAT_TRANSACTION);
 	}
+
+	if (oneway && frozen)
+		return BR_TRANSACTION_PENDING_FROZEN;
 
 	return 0;
 }
···
 	} else {
 		BUG_ON(target_node == NULL);
 		BUG_ON(t->buffer->async_transaction != 1);
-		binder_enqueue_thread_work(thread, tcomplete);
 		return_error = binder_proc_transaction(t, target_proc, NULL);
-		if (return_error)
+		/*
+		 * Let the caller know when async transaction reaches a frozen
+		 * process and is put in a pending queue, waiting for the target
+		 * process to be unfrozen.
+		 */
+		if (return_error == BR_TRANSACTION_PENDING_FROZEN)
+			tcomplete->type = BINDER_WORK_TRANSACTION_PENDING;
+		binder_enqueue_thread_work(thread, tcomplete);
+		if (return_error &&
+		    return_error != BR_TRANSACTION_PENDING_FROZEN)
 			goto err_dead_proc_or_thread;
 	}
 	if (target_thread)
···
 			binder_stat_br(proc, thread, cmd);
 		} break;
 		case BINDER_WORK_TRANSACTION_COMPLETE:
+		case BINDER_WORK_TRANSACTION_PENDING:
 		case BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT: {
 			if (proc->oneway_spam_detection_enabled &&
 				   w->type == BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT)
 				cmd = BR_ONEWAY_SPAM_SUSPECT;
+			else if (w->type == BINDER_WORK_TRANSACTION_PENDING)
+				cmd = BR_TRANSACTION_PENDING_FROZEN;
 			else
 				cmd = BR_TRANSACTION_COMPLETE;
 			binder_inner_proc_unlock(proc);
···
 	"BR_FAILED_REPLY",
 	"BR_FROZEN_REPLY",
 	"BR_ONEWAY_SPAM_SUSPECT",
+	"BR_TRANSACTION_PENDING_FROZEN"
 };
 
 static const char * const binder_command_strings[] = {

drivers/android/binder_internal.h

···
 };
 
 struct binder_stats {
-	atomic_t br[_IOC_NR(BR_ONEWAY_SPAM_SUSPECT) + 1];
+	atomic_t br[_IOC_NR(BR_TRANSACTION_PENDING_FROZEN) + 1];
 	atomic_t bc[_IOC_NR(BC_REPLY_SG) + 1];
 	atomic_t obj_created[BINDER_STAT_COUNT];
 	atomic_t obj_deleted[BINDER_STAT_COUNT];
···
 	enum binder_work_type {
 		BINDER_WORK_TRANSACTION = 1,
 		BINDER_WORK_TRANSACTION_COMPLETE,
+		BINDER_WORK_TRANSACTION_PENDING,
 		BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT,
 		BINDER_WORK_RETURN_ERROR,
 		BINDER_WORK_NODE,

include/uapi/linux/android/binder.h

···
 
 	BR_FROZEN_REPLY = _IO('r', 18),
 	/*
-	 * The target of the last transaction (either a bcTRANSACTION or
+	 * The target of the last sync transaction (either a bcTRANSACTION or
 	 * a bcATTEMPT_ACQUIRE) is frozen.  No parameters.
 	 */
 
···
 	 * Current process sent too many oneway calls to target, and the last
 	 * asynchronous transaction makes the allocated async buffer size exceed
 	 * detection threshold.  No parameters.
+	 */
+
+	BR_TRANSACTION_PENDING_FROZEN = _IO('r', 20),
+	/*
+	 * The target of the last async transaction is frozen.  No parameters.
 	 */
 };