Subject: Re: [PATCH 2/5] firewire: core: add local API to queue work item to workqueue specific to isochronous contexts

From: Takashi Iwai <[email-masked]>
Date: Wed, 04 Sep 2024 18:07:20 +0200

On Wed, 04 Sep 2024 14:51:51 +0200,
Takashi Sakamoto wrote:
> 
> In the previous commit, the workqueue is added per the instance of fw_card
> structure for isochronous contexts. The workqueue is designed to be used by
> the implementation of fw_card_driver structure underlying the fw_card.
> 
> This commit adds some local APIs to be used by the implementation.
> 
> Signed-off-by: Takashi Sakamoto <[email-masked]>
> ---
>  drivers/firewire/core-iso.c | 30 ++++++++++++++++++++++++++++--
>  drivers/firewire/core.h     | 10 ++++++++++
>  include/linux/firewire.h    |  1 +
>  3 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firewire/core-iso.c b/drivers/firewire/core-iso.c
> index 101433b8bb51..af76fa1823f1 100644
> --- a/drivers/firewire/core-iso.c
> +++ b/drivers/firewire/core-iso.c
> @@ -211,21 +211,47 @@ EXPORT_SYMBOL(fw_iso_context_queue_flush);
>  
>  int fw_iso_context_flush_completions(struct fw_iso_context *ctx)
>  {
> +	int err;
> +
>  	trace_isoc_outbound_flush_completions(ctx);
>  	trace_isoc_inbound_single_flush_completions(ctx);
>  	trace_isoc_inbound_multiple_flush_completions(ctx);
>  
> -	return ctx->card->driver->flush_iso_completions(ctx);
> +	might_sleep();
> +
> +	// Avoid dead lock due to programming mistake.
> +	if (WARN_ON(current_work() == &ctx->work))
> +		return 0;

Maybe WARN_ON_ONCE() would be safer if it's supposed to be called
frequently.  Otherwise it can spam too much.
Ditto for fw_iso_context_stop().

thanks,

Takashi