linux-kernel - Re: [PATCH v5 6/9] ALSA: virtio: PCM substream operators

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Date:   Thu, 25 Feb 2021 23:19:31 +0100
From:   Anton Yakovlev <anton.yakovlev@...nsynergy.com>
To:     Takashi Iwai <tiwai@...e.de>, "Michael S. Tsirkin" <mst@...hat.com>
CC:     <virtualization@...ts.linux-foundation.org>,
        <alsa-devel@...a-project.org>, <virtio-dev@...ts.oasis-open.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 6/9] ALSA: virtio: PCM substream operators

On 25.02.2021 21:30, Takashi Iwai wrote:> On Thu, 25 Feb 2021 20:02:50 
+0100,
> Michael S. Tsirkin wrote:
>>
>> On Thu, Feb 25, 2021 at 01:51:16PM +0100, Takashi Iwai wrote:
>>> On Thu, 25 Feb 2021 13:14:37 +0100,
>>> Anton Yakovlev wrote:


[snip]


>> Takashi given I was in my tree for a while and I planned to merge
>> it this merge window.
> 
> Hmm, that's too quick, I'm afraid.  I see still a few rough edges in
> the code.  e.g. the reset work should be canceled at the driver
> removal, but it's missing right now.  And that'll become tricky
> because the reset work itself unbinds the device, hence it'll get
> stuck if calling cancel_work_sync() at remove callback.

Yes, you made a good point here! In this case, we need some external
mutex for synchronization. This is just a rough idea, but maybe
something like this might work:

struct reset_work {
     struct mutex mutex;
     struct work_struct work;
     struct virtio_snd *snd;
     bool resetting;
};

static struct reset_work reset_works[SNDRV_CARDS];

init()
     // init mutexes and workers


virtsnd_probe()
     snd_card_new(snd->card)
     reset_works[snd->card->number].snd = snd;


virtsnd_remove()
     mutex_lock(reset_works[snd->card->number].mutex)
     reset_works[snd->card->number].snd = NULL;
     resetting = reset_works[snd->card->number].resetting;
     mutex_unlock(reset_works[snd->card->number].mutex)

     if (!resetting)
         // cancel worker reset_works[snd->card->number].work
     // remove device


virtsnd_reset_fn(work)
     mutex_lock(work->mutex)
     if (!work->snd)
         // do nothing and take an exit path
     work->resetting = true;
     mutex_unlock(work->mutex)

     device_reprobe()

     work->resetting = false;


interrupt_handler()
     schedule_work(reset_works[snd->card->number].work);


What do you think?


-- 
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin