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

[Anton Yakovlev]

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