netdev - Re: [PATCH 45/50] sound: usb: usx2y: spin

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Message-ID: <s5h7ggx413u.wl%tiwai@suse.de>
Date:	Thu, 11 Jul 2013 16:34:13 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, Oliver Neukum <oliver@...kum.org>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-input@...r.kernel.org, linux-bluetooth@...r.kernel.org,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	linux-media@...r.kernel.org, alsa-devel@...a-project.org,
	Jaroslav Kysela <perex@...ex.cz>
Subject: Re: [PATCH 45/50] sound: usb: usx2y: spin_lock in complete() cleanup

At Thu, 11 Jul 2013 22:13:35 +0800,
Ming Lei wrote:
> 
> On Thu, Jul 11, 2013 at 9:50 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > 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@...ex.cz>
> >> > Cc: Takashi Iwai <tiwai@...e.de>
> >> > Cc: alsa-devel@...a-project.org
> >> > Signed-off-by: Ming Lei <ming.lei@...onical.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().
> 
> Please use snd_pcm_stream_lock_irqsave() so that I can avoid sending
> out similar patch later, :-)
> 
> >
> > I'll prepare the patch for 3.11 independently from your patch series,
> > so please drop this one.
> 
> OK, thanks for dealing with that.
> 
> >
> >
> > BTW, the word "cleanup" in the subject is inappropriate.  This is
> > rather a fix together with the core change.
> 
> It is a cleanup since the patchset only addresses lock problem which
> is caused by the tasklet conversion.

Well, the conversion to irqsave() is needed for the future drop of
irq_save() in the caller, right?  Then this isn't a cleanup but a
preparation for movement ahead.


> > 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.
> 
> Interrupt is't enabled until all current drivers are cleaned up, so it is really
> safe, please see patch [2].

OK.

> > 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.
> 
> We discussed the problem in the below link previously[1], Steven
> and Thomas suggested to use threaded irq handler, but which
> may degrade USB mass storage performance, so we have to
> take tasklet now until we rewrite transport part of USB mass storage
> driver.
> 
> Also the conversion[2] has avoided the tasklet spin lock problem
> already.

OK, good to know.


thanks,

Takashi


> [1], http://marc.info/?t=137079119200001&r=1&w=2
> [2], http://marc.info/?l=linux-usb&m=137286326726326&w=2
> 
> Thanks,
> --
> Ming Lei
> 
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