Re: ufs: setting "hba" private pointer too late -- oops in ufshcd_devfreq_get_dev_status()

[Alexey Dobriyan <adobriyan@gmail.com>]

On Wed, Nov 10, 2021 at 10:18:15AM -0800, Bart Van Assche wrote:
> On 11/10/21 6:32 AM, Alexey Dobriyan wrote:
> > I've stumbled into a race while working on an earlier kernel,
> > but it looks like mainline is affected as well.
> > 
> >          err = ufshcd_init(hba, mmio_base, irq);
> > 		async_schedule(ufshcd_async_scan, hba);
> > 		ufshcd_add_lus(hba);
> > 		if (ufshcd_is_clkscaling_supported(hba)) {
> > 			[enable devfreq]
> > 
> >          platform_set_drvdata(pdev, hba);
> > 
> > Device's private pointer is set too late, as devfreq hook get HBA
> > pointer from private data and uses it:
> > 
> > 	static int ufshcd_devfreq_get_dev_status(struct device *dev, struct devfreq_dev_status *stat)
> > 	{
> > 	        struct ufs_hba *hba = dev_get_drvdata(dev);
> > 		if (!ufshcd_is_clkscaling_supported(hba))
> > 			return -EINVAL;
> > 
> > Unable to handle kernel NULL pointer dereference at virtual address ...0f10
> > pc :	ufshcd_devfreq_get_dev_status
> > lr :	devfreq_simple_ondemand_func
> > 	update_devfreq
> > 	devfreq_monitor
> > 
> > 
> > I reproduced it by turning async LU scan into sync, so it is easier to
> > trigger.
> 
> Hi Alexey,
> 
> Thanks for having reported this. Do you perhaps plan to post a patch to fix
> this?

Not really, my workaround is

	if (!hba) {
		return -EINVAL;
	}

But it is likely incorrect.