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Date:   Wed, 23 Nov 2022 18:58:29 +0000
From:   Carlos Llamas <cmllamas@google.com>
To:     Li Li <dualli@chromium.org>
Cc:     dualli@google.com, gregkh@linuxfoundation.org, arve@android.com,
        tkjos@android.com, maco@android.com, joel@joelfernandes.org,
        brauner@kernel.org, surenb@google.com, arnd@arndb.de,
        masahiroy@kernel.org, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org, hridya@google.com,
        smoreland@google.com, kernel-team@android.com
Subject: Re: [PATCH v2 1/1] binder: return pending info for frozen async txns
Message-ID: <Y35tVQb2y+gRdfpb@google.com>
References: <20221110203405.611600-1-dualli@chromium.org>
 <20221110203405.611600-2-dualli@chromium.org>
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On Thu, Nov 10, 2022 at 12:34:05PM -0800, Li Li wrote:
> From: Li Li <dualli@google.com>
> 
> 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.
> 
> Signed-off-by: Li Li <dualli@google.com>
> ---
>  drivers/android/binder.c            | 31 +++++++++++++++++++++++------
>  drivers/android/binder_internal.h   |  3 ++-
>  include/uapi/linux/android/binder.h |  7 ++++++-
>  3 files changed, 33 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 880224ec6abb..a798f6661488 100644
> --- a/drivers/android/binder.c
> +++ b/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 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;
> +
>  	return 0;
>  }
>  
> @@ -3607,9 +3615,16 @@ 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)
> +			tcomplete->type = BINDER_WORK_TRANSACTION_PENDING;
> +		binder_enqueue_thread_work(thread, tcomplete);
> +		if (return_error && return_error != BR_TRANSACTION_PENDING)
>  			goto err_dead_proc_or_thread;
>  	}
>  	if (target_thread)
> @@ -4440,10 +4455,13 @@ 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;
>  			else
>  				cmd = BR_TRANSACTION_COMPLETE;
>  			binder_inner_proc_unlock(proc);
> @@ -6170,6 +6188,7 @@ static const char * const binder_return_strings[] = {
>  	"BR_FAILED_REPLY",
>  	"BR_FROZEN_REPLY",
>  	"BR_ONEWAY_SPAM_SUSPECT",
> +	"BR_TRANSACTION_PENDING"
>  };
>  
>  static const char * const binder_command_strings[] = {
> diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
> index abe19d88c6ec..6c51325a826f 100644
> --- a/drivers/android/binder_internal.h
> +++ b/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) + 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,
> diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
> index e72e4de8f452..c21b3b3eb4e4 100644
> --- a/include/uapi/linux/android/binder.h
> +++ b/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 = _IO('r', 20),
> +	/*
> +	 * The target of the last async transaction is frozen.  No parameters.
> +	 */
>  };
>  
>  enum binder_driver_command_protocol {
> -- 
> 2.38.1.431.g37b22c650d-goog
> 

This looks good. Could you rename the new op to signify the frozen
scenario though? We might have some other instances of pending
transactions in the future so might as well be specific here.