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 <dualli@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20221123201654.589322-2-dualli@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -2728,7 +2728,10 @@ binder_find_outdated_transaction_ilocked(struct binder_transaction *t,
  *
  * 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,
@@ -2738,6 +2741,7 @@ static int binder_proc_transaction(struct binder_transaction *t,
 	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);
@@ -2751,15 +2755,16 @@ static int binder_proc_transaction(struct binder_transaction *t,
 
 	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)
@@ -2770,7 +2775,7 @@ static int binder_proc_transaction(struct binder_transaction *t,
 	} 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) {
@@ -2807,6 +2812,9 @@ static int binder_proc_transaction(struct binder_transaction *t,
 		binder_stats_deleted(BINDER_STAT_TRANSACTION);
 	}
 
+	if (oneway && frozen)
+		return BR_TRANSACTION_PENDING_FROZEN;
+
 	return 0;
 }
 
@@ -3607,9 +3615,17 @@ static void binder_transaction(struct binder_proc *proc,
 	} 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)
@@ -4440,10 +4456,13 @@ static int binder_thread_read(struct binder_proc *proc,
 			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);
@@ -6159,6 +6178,7 @@ static const char * const binder_return_strings[] = {
 	"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

@@ -133,7 +133,7 @@ enum binder_stat_types {
 };
 
 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];
@@ -152,6 +152,7 @@ struct binder_work {
 	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

@@ -450,7 +450,7 @@ enum binder_driver_return_protocol {
 
 	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.
 	 */
 
@@ -460,6 +460,11 @@ enum binder_driver_return_protocol {
 	 * 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.
+	 */
 };
 
 enum binder_driver_command_protocol {