Re: [PATCH v7 8/8] dmaengine: idxd: fix cdev setup and free device lifetime issues

[Dan Williams <dan.j.williams@intel.com>]

On Mon, Mar 22, 2021 at 4:32 PM Dave Jiang <dave.jiang@intel.com> wrote:
>
> The char device setup and cleanup has device lifetime issues regarding when
> parts are initialized and cleaned up. The initialization of struct device is
> done incorrectly. device_initialize() needs to be called on the 'struct
> device' and then additional changes can be added. The ->release() function
> needs to be setup via device_type before dev_set_name() to allow proper
> cleanup. The change re-parents the cdev under the wq->conf_dev to get
> natural reference inheritance. No known dependency on the old device path exists.
>
> Reported-by: Jason Gunthorpe <jgg@nvidia.com>
> Fixes: 42d279f9137a ("dmaengine: idxd: add char driver to expose submission portal to userland")
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
[..]
> diff --git a/drivers/dma/idxd/sysfs.c b/drivers/dma/idxd/sysfs.c
> index 03079ff54889..8a08988ea9d1 100644
> --- a/drivers/dma/idxd/sysfs.c
> +++ b/drivers/dma/idxd/sysfs.c
> @@ -1174,8 +1174,14 @@ static ssize_t wq_cdev_minor_show(struct device *dev,
>                                   struct device_attribute *attr, char *buf)
>  {
>         struct idxd_wq *wq = container_of(dev, struct idxd_wq, conf_dev);
> +       int minor = -1;
>
> -       return sprintf(buf, "%d\n", wq->idxd_cdev.minor);
> +       mutex_lock(&wq->wq_lock);
> +       if (wq->idxd_cdev)
> +               minor = wq->idxd_cdev->minor;
> +       mutex_unlock(&wq->wq_lock);
> +
> +       return sprintf(buf, "%d\n", minor);

As I mentioned, let's not emit a negative value here. ...not that
userspace should be using this awkward recreation of the existing core
'dev' attribute anyway.

if (minor == -1)
    return -ENXIO;
return sprintf(buf, "%d\n", minor);