Date: Thu, 11 Jul 2013 15:50:57 +0200
Message-ID: <s5hip0hb3y6.wl%tiwai@suse.de> (sfid-20130711_154945_055680_B020A66A)
From: Takashi Iwai <tiwai@suse.de>
To: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Ming Lei <ming.lei@canonical.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, Oliver Neukum <oliver@neukum.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-input@vger.kernel.org, linux-bluetooth@vger.kernel.org,
	netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
	linux-media@vger.kernel.org, alsa-devel@alsa-project.org,
	Jaroslav Kysela <perex@perex.cz>
Subject: Re: [PATCH 45/50] sound: usb: usx2y: spin_lock in complete() cleanup
In-Reply-To: <51DEAE4E.90204@cogentembedded.com>
References: <1373533573-12272-1-git-send-email-ming.lei@canonical.com>
	<1373533573-12272-46-git-send-email-ming.lei@canonical.com>
	<51DEAE4E.90204@cogentembedded.com>
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At Thu, 11 Jul 2013 17:08:30 +0400,
Sergei Shtylyov wrote:
> 
> On 11-07-2013 13:06, Ming Lei wrote:
> 
> > Complete() will be run with interrupt enabled, so change to
> > spin_lock_irqsave().
> 
>     Changelog doesn't match the patch.

Yep, but moreover...

> > Cc: Jaroslav Kysela <perex@perex.cz>
> > Cc: Takashi Iwai <tiwai@suse.de>
> > Cc: alsa-devel@alsa-project.org
> > Signed-off-by: Ming Lei <ming.lei@canonical.com>
> > ---
> >   sound/usb/usx2y/usbusx2yaudio.c |    4 ++++
> >   1 file changed, 4 insertions(+)
> 
> > diff --git a/sound/usb/usx2y/usbusx2yaudio.c b/sound/usb/usx2y/usbusx2yaudio.c
> > index 4967fe9..e2ee893 100644
> > --- a/sound/usb/usx2y/usbusx2yaudio.c
> > +++ b/sound/usb/usx2y/usbusx2yaudio.c
> > @@ -273,7 +273,11 @@ static void usX2Y_clients_stop(struct usX2Ydev *usX2Y)
> >   		struct snd_usX2Y_substream *subs = usX2Y->subs[s];
> >   		if (subs) {
> >   			if (atomic_read(&subs->state) >= state_PRERUNNING) {
> > +				unsigned long flags;
> > +
> > +				local_irq_save(flags);
> >   				snd_pcm_stop(subs->pcm_substream, SNDRV_PCM_STATE_XRUN);
> > +				local_irq_restore(flags);
> >   			}

... actually this snd_pcm_stop() call should have been covered by
snd_pcm_stream_lock().  Maybe it'd be enough to have a single patch
together with the change, i.e. wrapping with
snd_pcm_stream_lock_irqsave().

I'll prepare the patch for 3.11 independently from your patch series,
so please drop this one.


BTW, the word "cleanup" in the subject is inappropriate.  This is
rather a fix together with the core change.

And, I wonder whether we can take a safer approach.  When the caller
condition changed, we often introduced either a different ops
(e.g. ioctl case) or a flag for the new condition, at least during the
transition period.

Last but not least, is a conversion to tasklet really preferred?
tasklet is rather an obsoleted infrastructure nowadays, and people
don't recommend to use it any longer, AFAIK.


thanks,

Takashi