linux-kernel - Re: [PATCH v5 2/9] ALSA: virtio: add virtio sound driver

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Date:   Thu, 25 Feb 2021 11:38:35 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Anton Yakovlev <anton.yakovlev@...nsynergy.com>
Cc:     <virtualization@...ts.linux-foundation.org>,
        <alsa-devel@...a-project.org>, <virtio-dev@...ts.oasis-open.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Jason Wang <jasowang@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/9] ALSA: virtio: add virtio sound driver

On Mon, 22 Feb 2021 16:34:37 +0100,
Anton Yakovlev wrote:
> +static int virtsnd_find_vqs(struct virtio_snd *snd)
> +{
> +	struct virtio_device *vdev = snd->vdev;
> +	vq_callback_t *callbacks[VIRTIO_SND_VQ_MAX] = {
> +		[VIRTIO_SND_VQ_EVENT] = virtsnd_event_notify_cb
> +	};
> +	const char *names[VIRTIO_SND_VQ_MAX] = {

Shouldn't be static?
Also it's often const char * const names[] = { ... }
unless you overwrite something.

> +/**
> + * virtsnd_reset_fn() - Kernel worker's function to reset the device.
> + * @work: Reset device work.
> + *
> + * Context: Process context.
> + */
> +static void virtsnd_reset_fn(struct work_struct *work)
> +{
> +	struct virtio_snd *snd =
> +		container_of(work, struct virtio_snd, reset_work);
> +	struct virtio_device *vdev = snd->vdev;
> +	struct device *dev = &vdev->dev;
> +	int rc;
> +
> +	dev_info(dev, "sound device needs reset\n");
> +
> +	/*
> +	 * It seems that the only way to properly reset the device is to remove
> +	 * and re-create the ALSA sound card device.
> +	 */
> +	rc = device_reprobe(dev);
> +	if (rc)
> +		dev_err(dev, "failed to reprobe sound device: %d\n", rc);

Now I'm wondering whether it's safe to do that from this place.
Basically device_reprobe() unbinds the device that releases the full
resources once including the devm_* stuff.  And this work itself is in
a part of devm allocated resource, so it'll be released there.  That
said, we might hit use-after-free...  This needs to be verified.


thanks,

Takashi