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

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Message-ID: <20240905080711.GA486563@workstation.local>
Date: Thu, 5 Sep 2024 17:07:11 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: Takashi Iwai <tiwai@...e.de>
Cc: linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org,
	apais@...ux.microsoft.com, edmund.raile@...tonmail.com,
	linux-media@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/5] firewire: core: add local API to queue work item to
 workqueue specific to isochronous contexts

Hi,

On Wed, Sep 04, 2024 at 06:07:20PM +0200, Takashi Iwai wrote:
> 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 <o-takashi@...amocchi.jp>
> > ---
> >  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 for your suggestion. Indeed, the kernel API would be called so
frequently, and the *_ONCE macro would be safer. I'll post another patch
for it, since posting updated series of changes to all of receivers is a
bit cumbersome to me...


Thanks

Takashi Sakamoto